The previous article was all about the process of inflammation. This article is about vaccines.

The vaccines fall under the type of artificial active acquired immunity. This is artificial because we are giving the vaccine externally and this is active because the body is generating the antibodies/response and it is acquired because we are getting the immunity and it is not present by birth. You must have known what immunity is at least by now.

A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins (antigens). So these vaccines are nothing but the pathogen itself but it cannot cause any disease, instead, it triggers the immune system.

This is a quick recap of the principle of working on vaccines. The vaccine contains the pathogens as a whole or the surface antigens only. These antigens stimulate the immune system. If the immune system had a memory about this antigen, then it would immediately produce an antibody, and phagocytosis of the antigen occurs by the macrophage aided by the antibody. In this scenario, the antigen is new and there is no memory, therefore the immune system struggles and takes time to produce the antibody.

So the antigen reign over the body and this can lead to inflammation. As a result, some of the symptoms of inflammation like fever, heat, pain in the area of application, and swelling may appear. The chances of them are rare and also severity is less (last for a few hours/days) since the pathogen is attenuated.

Once the immune system produces the correct antibody, phagocytosis of the antigen occurs and hence the causative agent is eliminated from the body (primary response). So if the same or similar pathogen which has disease-causing ability enters into the body, the memory triggers the immune system to produce the correct antibody. So a heightened and rapid response is generated in order to kick away the pathogen quickly (secondary response).

There are three types of vaccines:-

Live- infection is caused without any harm – measles & polio

Dead- doesn’t last long, requires booster dose- cholera

Microbial products- involves non-infectious pathogen, capsule and toxoid- anthrax, diptheria

Hence using the vaccine as a stimulus, the body is able to generate a response that is stored and can be useful for preventing the disease caused by the pathogen.

There might be an idea to generate vaccines for all diseases so that all humans are protected. But there are some difficulties in this which are listed below:-

There are new microbes being discovered every day and no one knows which microbe can cause disease. There can be multiple microbes causing the same or similar disease. So being immune to one microbe doesn’t mean being immune to the disease

The disease-causing microbe can undergo mutation meaning that there can be changes in the genetic material and hence the antigen can change. In this case, the antibody which was stimulated by the vaccine won’t work. A suitable example is a common cold, it is impossible to produce a vaccine that covers all mutants of viruses

The pathogen has to be genetically modified so as to remove its disease-causing ability which is easy to say but difficult to implement

Also, it is important that the antigen chose for the vaccine must be close to that of the original causative agent of the disease. If the original pathogen is not so close to that of the vaccine, then it will not work

Hence all these above points explain the difficulties in producing a vaccine. Despite these many research organizations in many countries have produced vaccines especially for the pandemic and dreadful diseases like the COVID-19, hepatitis, polio, etc. in which some vaccines provide lifetime immunity to some of the diseases. We must take a minute to appreciate those who have done immense work and their contribution is stopping some of the dreadful diseases.

With this, we come to the end of the series. I hope that all the concepts explained in this were simple and clear and also would have inculcated an interest in immunology. By now, it would be clear how the immune system protects us from several microbes and diseases.

HAPPY LEARNING!!

The previous article dealt with the types and functions of immunoglobulin. This article provides a complete explanation of the process of inflammation.

Inflammation is the process of protection which was seen as one of the six mechanisms of innate immunity.

Inflammation is one of the body’s responses to the invasion of foreign particles. This is an important process in the human body that occurs to drive away from the pathogen. Inflammation is one of the stages seen in healing. Some of the changes that can be seen in the target site are:-

• Changes in blood flow (mostly blood loss)
• Increase in platelets (to plug the damaged vessel)
• Increase in immune cells
• Supply of nutrients

The word inflammation refers to a burning sensation. Hence there are five cardinal signs in inflammation namely:-

• Rubor (redness)
• Tumor (swelling)
• Calor (heat)
• Dolor (pain)
• Functioleasia (loss of function)

These cardinal signs as well as the changes occur due to some mediators which are basically chemicals and also due to the action of various immune cells.

This inflammation can be either acute or chronic. As seen earlier, acute stays for a shorter time but produces more vigorous pain whereas chronic stays for a longer time with less vigorous pain. If the causative agent has been driven away then healing occurs either by complete restoration or scar formation. There are chances that the acute inflammation can become chronic which can be worse. It can lead to several diseases and complications.

The pathogen in order to establish its supremacy in the human body, it has to pass through the epidermis which is the outermost layer of the human body. This is known as SALT skin-associated lymphoid tissues. Hence T and B lymphocytes are prominent in the skin. Most of the pathogens get destroyed in this stage. Let us assume that our pathogen is strong and it had passed through it. The next layer it encounters is the dermis. As we go deep inside the skin, more and more immune cells get involved. In the dermis the following immune cells are seen:-

• Macrophage
• NK cells
• Mast cell – produce histamine and serotonin
• T helper cells – it provides help to other immune cells

The next stage is the hypodermis which has a large number of macrophages and neutrophils that phagocytosis the pathogen. Hence these following processes help in defending against the pathogens.

When a particular pathogen say a virus enters the cell, the immune system will get alerted through signals and they immediately send the correct immune cell to the target site. This occurs since either the immune system gets information naturally or artificially through previous infection or vaccine. This leads to the classification of immunity in humans.

So now we will consider a new and strong pathogen that has not been recognized by the immune system and has dodged those barriers and has entered inside the skin. Now it multiplies at a rapid rate and colonizes that particular area. Hence the cells in that area start to die and they release several signals like TNF, cytokines, interleukins. This gets combined with other signals like histamine, serotonin released from immune cells. Some of these signals produce direct effects on the target site as seen in the table.

An array of these signals triggers the immune system and it, in turn, starts the inflammation process and the cardinal signs are observed. This process lasts for some time and as it occurs; the pathogens decrease in number through phagocytosis and subsequently vanishes from the body. This can be observed by a decrease in the signs. After this process, the targeted site starts to heal and the immune system learns how to defend the pathogen when it enters the next time.

Now the damage caused by the pathogen has to be repaired by the process of healing.

1. Haemostasis
2. Inflammation
3. Proliferation
4. Maturation/Remodelling

The pathogen will rupture and damage the outer layer of blood vessels known as endothelium resulting in blood loss. Hence the blood vessels start to contract to prevent further loss. Also, a plug is formed at the site of leakage by the platelets. Then the process of inflammation occurs; clearing out the dead cells and the pathogen. In the proliferative stage, new blood cells are formed by a process known as neovascularisation and the new epithelium is formed. In the last phase, the newly formed cells become stronger and flexible. Hence the combination of these steps brings the affected area back to normal.

Hence the inflammation is an essential process in the immune system and it has to occur to prevent the conspiracy of the microbes. The next article is about vaccines and their principle of working.

HAPPY READING!!!

The previous article dealt in detail with immunoglobulin and how they help in phagocytosis. This article is about the types of immunoglobulins, their functions.

The types of immunoglobulins are based on the types of light and heavy chains. There are two types of light chains namely the kappa and the lambda. An immunoglobulin contains either kappa (K-K) or lambda (L-L) but does not have a mixture of both (K-L not possible). About 60% of the immunoglobulins in humans have kappa chains.

So, the classes of immunoglobulins are based on the heavy chain. So based on this condition, there are five classes of immunoglobulins namely:-

• Immunoglobulin G (IgG) – gamma
• Immunoglobulin M (IgM) – mu
• Immunoglobulin A (IgA) – alpha
• Immunoglobulin D (IgD) – delta
• Immunoglobulin E (IgE) – epsilon

These immunoglobulins have certain configurations and play different roles in the human body. The immunoglobulin G is present the most. It constitutes about 80% of the total immunoglobulin. These are mostly present in the blood, plasma, and other body fluids. This immunoglobulin has the lowest carbohydrate content when compared to the rest. This immunoglobulin has a half-life of 23 days which is the longest of all. Some of the unique features and functions of this immunoglobulin:-

• This is the only immunoglobulin which can cross the placenta (this is a unique feature because this immunoglobulin provides immunity to the foetus inside the womb and also after birth for some months. Presence of others may indicate infection)
• This helps in killing bacteria and viruses by opsonisation (the process of covering the pathogen with a protein coat such that the pathogens become more presentable to the immune cells)
• Neutralize toxins
• Activate complement by classical pathway (The complement system, also known as complement cascade, is a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen’s cell membrane)
• Unique catabolism (breaking down of molecules) based on concentration
• There are four sub classes (G1, G2, G3 and G4) out of which 1,3 and 4 cross the placenta and offer immunity
• Also involves in the Rh immunization (there are two types’ Rh+ve and Rh-ve based on the presence of Rh factor in blood). The mother being Rh+ve and child the opposite is not a problem in the first pregnancy but can be fatal in second, killing the foetus.

The immunoglobulin M constitutes about 5-10% of total proteins. This is a pentamer structure with a J chain. This weighs about 900000-1000000 and is the heaviest of all. They have 5 days of half-life. Some of its features-

• Presence in newborn indicate congenital infection as they don’t cross placenta
• Short lived, so their presence indicates recent infection
• First Ig to participate in primary response
• Opsonisation
• classical pathway
• bacteria agglutination
• Play an important role in ABO blood grouping (discovered by Landsteiner). There are 8 types of blood groups based on antigen, antibody and Rh factor

Immunoglobulin A is also known as the secretory immunoglobulin and is mostly present in body secretions (tear, saliva, sebum, mucous, and milk) in which they are dimer and are monomer in blood. They constitute 10-15% of the proteins. They also have a J chain and secretory piece. Their half-life is 6-8 days.

• The secretory piece protects the Ig from enzymes and juices
• Complement activation by alternate pathway
• Promote phagocytosis
• Intracellular microorganism killing
• First line of defense against some microbes

Immunoglobulin E is a dimer similar to IgG. This is present in low concentrations (about 0.3) and has the weight of about 1,90,000. These have a half-life of about 2 days and can become inactivated at 56 C.

• Present extra-cellularly
• Associated with allergic reactions like asthma, hay fever and anaphylactic shock
• Bind with the Fc of mast cells and basophils resulting in degranulation and release histamine which causes allergy
• Mediate the some immunity reactions
• No complement activation
• Provide immunity against helminthes

The last is immunoglobulin D.  It is present in low concentrations and on the surface of B lymphocytes. They constitute 0.2% of proteins. They have a half-life of 3 days. The IgM and IgD bind on the B lymphocyte to help in antigen identification.

Hence these were the different types of immunoglobulins and the mechanisms by which they help with immunity. The next article is about the process of inflammation.

HAPPY READING!!

The previous article was about the different types of immune cells. This article is about a special molecule in immunity known as immunoglobulin.

There might be a question that what is so special about this immunoglobulin. There is a reason for this. These molecules play an important and inevitable role in the phagocytosis of pathogens. To understand this, it is essential to know about immunoglobulins.

The immunoglobulin is a gamma globulin, a specialized group of proteins (glycoprotein) produced in response to pathogens. It is produced by the plasma cells (a globulin protein present in the plasma). These constitute 25-30% of the blood proteins.

There are two important terms that are more commonly known by the most, they are the antigen and the antibody. The antigen is the molecule present on the surface of the pathogen and can stimulate an immune response. There is a small part of the antigen called the epitope which interacts with the antibody.  The epitope is known as the antigen determinant site. An antigen can have unlimited epitopes.

On the contrary, the antibody is the molecule produced in response to the antigen in order to kick it away. The part of the antibody which interacts with the antigen is called a paratope. An antibody must have at least 2 paratopes. These antibodies belong to the immunoglobulins. All antibodies are immunoglobulins but not immunoglobulins are antibodies. To understand how the antibody helps in immunity, it is essential to understand the structure of an antibody/immunoglobulin. The image below shows the general structure of an immunoglobulin:-

There are two chains in an immunoglobulin namely the light chain and heavy chain. The light chain has 212 amino acids (the building block of protein) and the heavy chain has 450 amino acids. Each chain has two types namely the constant and variable. These regions are based on the amino acid sequences. Half of the light chain (1 out of 2) is constant and the rest is variable. A quarter of the heavy chain (1 out of 4) is variable and the rest is constant. These are linked by two types of sulfide bonds namely the intra (H-H AND L-L) and inter (H-L). These molecules contain carbohydrates (CHO) hence these are called as glycoproteins.

The tip of the variable regions of the heavy and light chain is hypervariable in nature and these constitute the antigen-binding site (Fab). These are hyper-variable because they have to produce amino acid sequences complementary to that of the antigen so that they can interact together. The other site is called a crystallizable region (Fc).

Having known all this, now it will be convenient to explain the process by which the antibody plays in the prevention of infections.

There are millions of substances that pass through the blood every day. So there must be a criterion/substance to identify them whether they are pathogenic. This is where antigen comes to play. These antigens present on the surface of the pathogens alert the immune system which then identifies this as a pathogen. So in response to the antigen, a suitable antibody is secreted and deployed to the target site. On reaching the antigen, the Fab region binds with the antigen.

The ultimate aim of the immune system is to abolish the pathogen and one way is by phagocytosing them. This is done by the macrophages. But it is essential for them to identify the substance before engulfing it. This is where the antibody comes to play. The Fc region of the antibody combines with the receptor of the macrophage. This facilitates the process of phagocytosis.

Hence the antibody acts like a bridge between the source (antigen) and the destination (macrophage) aiding in phagocytosis. This is essential because in most of the cases the macrophages, it is difficult to identify the non-self-objects and this is where antibody helps.

In the case of the new pathogen, the antigen is new, and therefore their might not be a suitable antibody. In that case, the macrophage cannot phagocytocise the pathogen and it reigns in the body causing infection and disease.

The next article is about the types of immunoglobulins.

HAPPY LEARNING!!

The previous article was about the acquired immunity. This article is all about the immune cells, the warriors of the human body.

These cells play a major role in protecting the body from infections. Some of them contribute directly and some contribute indirectly. Despite the methods, all of them are required in optimum amounts so as to live a healthy life.

All of these cells are derived from a specific type of cell found in the blood. The blood is a freely flowing interstitial fluid that transports oxygen, nutrients, etc. to the cells of the body. There are two components in the blood in which the first one is called plasma. The plasma is the liquid carrying water, salts, enzymes, and proteins. There are three specialized proteins in the plasma-

Albumin- to maintain water balance

Globulin- for immunity (it is a part of immunoglobulin)

Fibrinogen- for clotting

Hence the plasma also contributes to immunity. This plasma constitutes about 55% of the blood. The rest 45% of the blood is constituted by the formed elements or corpuscles. There are three elements in it namely-

Erythrocyte or Red Blood Corpuscle- transport of oxygen

Leucocyte or White Blood Corpuscle- fight infections

Thrombocyte or platelets- for clotting

Out of these, the WBC is the one primarily contributing to immunity. A healthy person must have a WBC count from 4000-11000. Count less than 4000 means leukopenia meaning that the immune system is weak. If the count is more than 11000 then it means the condition of autoimmunity known as leucocytosis. There are some further classifications in the WBC which are displayed through the flowchart below.

There are two types of cells in the WBC namely the granulocytes and agranulocytes.

The granulocytes, as the name specifies have granules in their cytoplasm. There are three different cells in this.

The neutrophil constitutes to about 55-70% of the total WBC and they are ones involved in most of the fights against the infections. These defend against bacterial and fungal infections. These cells are mostly found in the epidermal regions and are in the first line of defense.  These cells engulf the pathogens by the process of phagocytosis. These cells have multiple nuclei hence these are also known as PMN (Poly Morpho Neutrophils). Neutrophils help prevent infections by blocking, disabling, and digesting off invading particles and microorganisms. They also communicate with other cells to help them repair cells and mount a proper immune response. The death of these cells often results in the formation of pus (suppuration).

The eosinophil constitutes about 2-4% of the total WBC. These cells are very little in the body but can increase in the case of allergic reactions, parasite infection, and so on. The functions of the eosinophil include movement to inflamed areas, trapping substances, killing cells, anti-parasitic and bactericidal activity, participating in immediate allergic reactions, and modulating inflammatory responses.

The basophil is present in the least concentration of all (0.2%) in total WBC. These cells play an important role in allergic reactions in which their count can increase. The basophil contains inflammatory mediators like histamine and heparin. The release of the compounds results in dilation of the blood vessels. Hence these cells regulate the inflammation process.

The agranulocytes are those which lack granules in their cytoplasm. There are two types in this. The lymphocyte can be called as the memory of the immune system. There are two types of lymphocytes namely T and B lymphocytes. These lymphocytes recognize the incoming pathogens and based on their memory it produces a suitable response in a short amount of time. These cells are involved in the secondary response in the acquired immunity.

B cells make antibodies that can bind to pathogens, block pathogen invasion, activate the complement system, and enhance pathogen destruction. The T cells mostly known as CD4+ T helper cells produce the cytokines (proteins in cell signaling) and coordinate with the immune system. There is another form called CD8+ cytotoxic T cells which is opposite to the previous type, they help in the destruction of tumors and pathogens.

The monocyte is the largest of all the cells in WBC. They function similarly to that of the neutrophils (phagocytosis of the pathogens). These cells present the pathogen to the memory cells upon which a response is generated. Once they leave the blood, they turn into macrophages which help in clearing cell debris and killing pathogens. These are known as the vacuum cleaners of immunity.

Hence all these cells work in different mechanisms and they coordinate together to make sure that we do not fall prey to the disease-causing microorganisms.

HAPPY LEARNING!!

A detailed description of innate immunity has been provided in the previous article. This article explains in detail the action of innate immunity. As mentioned earlier, innate immunity is a non-specific immunity that acts as the first line of defence. There are six mechanisms backing innate immunity. They are:-

1. Epithelial surfaces
2. Antimicrobial products
3. Microbial antagonism
4. Cellular factors
5. Inflammation
6. Acute phase proteins

These are the six different mechanisms of innate immunity.

Epithelial surfaces

The epithelial surfaces are those which form the outermost layer of the body. It is pretty obvious that the pathogens gain access into the body through the body openings. Hence it is trivial that the immunity is strong at these places. The following are the body openings where the immunity is present:-

• Eyes
• Ears
• Nose
• Mouth
• Skin
• Genital tracts

Eyes– there is a special fluid called the ‘tear’ generated by the lacrimal apparatus. This tear can flush out the microbes by its mechanical action. Also, the enzyme called lysozyme is present in it which is antibacterial in nature. This particular enzyme splits certain polysaccharide molecules from the cell wall of the bacteria without which it cannot sustain. Hence these are processes that confer immunity to the eyes.

Ears– there is a constant production of wax that entraps the foreign microbes. The cells lining the outer surface of the ear membranes secrete the wax for cleaning and protective purposes. The inner ear is filled with phagocytic cells.

Nose– the nose and the respiratory pathway are very important to be protected since they involve the exchange of air and microbes can easily enter. So there is tightened defence provided by several mechanisms:-

• The anatomy of the nose itself prevents the entry of some microorganisms
• There is mucus lining the entire respiratory pathway which have hairs that can sweep the microbes back to the air
• There are mucopolysaccharides which are sticky in nature and hence the microbes get stuck to them
• The alveoli of the lungs are filled with phagocytic cells

Mouth– the mouth and the digestive system are also as important as the nose. The following defence mechanisms can be seen

• Saliva which is basic in nature kills some of the pathogens
• The peristalsis movement can kick away some of the microbes
• The stomach acid which is low in Ph can destroy most of the microbes
• The digestive juices and secretions like the bile also provide immunity

Skin- the skin is present all over the body and there are 4 mechanisms

• Long chain fatty acid
• Salty nature of the sweat
• Soaps contribution
• Oils and sebaceous glands

Genital tract- this is also an important opening to be concerned about as there is a large concentration of microbes found here. The urine itself flushes out any incoming pathogens. In males, the sperm protein spermine and zinc are antibacterial. In females, high acidity can kill the microbes.

Antimicrobial products

There are some anti-microbial products present naturally in the bloodstream and other body fluids.

• Beta lysine- effective against thermostable bacteris
• Polypeptides- leukin and plakin
• Lactic acid- muscles
• Lactoperoxidase- present in breast milk
• Interferons- effective against virus

Microbial antagonism

Remember the fact in the first article that the foreign microbe has to find a suitable ‘target site’. The reason is that there are already some microbes present inside us. Don’t worry they won’t hurt us. These microbes constitute the normal flora and are resident. They follow symbiotic relationships with us. A suitable example is an e.coli present in the intestine helping indigestion for food.

So the presence of one species of organisms do not allow the presence of similar or different species. So these microbes indirectly furnish immunity to the body. So nice of them!

Cellular factors

These are some cells that are specialised in the function of protecting the body by destroying pathogens. It is done by the process of phagocytosis which is the engulfing of substances. The phagocytising cells engulf the foreign particles in response to the chemical mediators (mediators are certain chemicals released by a special type of immune cell known as mast cell).

There is a special defence for viral infections. In this case, the interferons activate the NK cells (Natural Killer) to undergo phagocytosis. This cell can be called the assassin of the immune system.

Inflammation

Inflammation is one of the body’s responses to the invasion of foreign particles. This is an important process in the human body that occurs to drive away from the pathogen. Inflammation is one of the stages seen in healing. This inflammation can be either acute or chronic. Acute stay for a shorter time but produces more vigorous pain whereas chronic stays for a longer time with less vigorous pain. If the causative agent has been driven away then healing occurs either by complete restoration or scar formation. There are chances that the acute inflammation can become chronic which can be worse. It can lead to several diseases and complications.

Acute-phase proteins

These are certain indicator proteins present in the blood whose increase in the level indicates infections. A group of these proteins constitute the acute phase proteins. They are:-

• C-reactive protein
• Mannose binding factor
• Serum P amyloid component
• Alpha -1-acid antitrypsin

These proteins enhance the defence and host resistance, prevent tissue injury and aid in damage repairs.  

The next article deals in detail with another type of immunity, the acquired immunity.

HAPPY READING!!!

The previous article gave a brief introduction to immunity, the internal force protecting us from several hazards. This article will be on the classification of immunity.

This is the classification chart for immunity. Immunity can be briefly classified as two, innate immunity and the acquired immunity. Innate immunity also known as natural immunity and native immunity is the one that has been bestowed to us. This type of immunity is present from birth till death. The following are the other names of innate immunity:-

• Natural immunity
• Native immunity
• Non-specific immunity

Innate immunity is the resistance to infections which an individual possesses due to their genetics. Also, there are other factors that can decide native immunity.

Species- the native immunity which is present within everyone is species-specific. The meaning is that humans have resistance to a specific set of infections and the plants have resistance to another specific set of infections. This is the reason for which humans do not get affected by plant diseases and vice versa.

Race- race refers to the group of people from several parts of the world. People in one part of the world may be resistant to a particular disease when compared to others. This can also depend on the environmental conditions and other factors in which people reside. A suitable example for this is a study that shows that the Negroid species (of African origin) in the US are more resistant to tuberculosis when compared to the Caucasian species (European origin).

Individual- people having a similar genetic constitution may have the same resistance/non-resistance to infections. A study shows that twins have the same level of resistance and non-resistance to several diseases.

The innate immunity is long-lasting, non-specific, and has a good memory. The term memory will be explained while introducing the immune cells. Innate immunity forms the first line of defence in our body. This immunity primarily focuses on providing a barrier to the body and destroying the microbes and pathogens, irrespective of their type. Hence the innate immunity is known as non-specific immunity. There are specified cells that perform this activity and the process is known as phagocytosis. More details will be provided in the next article.

The innate immunity can be comprised of four namely. These can be known as the barriers of innate immunity:-

• Physical
• Physiological
• Cellular
• Cytokine

The physical type includes the mechanical barriers mostly present in the openings of the body (eye, nose, mouth, ears, genitals, and skin) which prevent the entry of microbes through several mechanisms.

The physiologic type includes the secretions of which help in kicking out the pathogens. These include sweat, highly acidic stomach acid, saliva, sebaceous glands, earwax, and mucus, and so on. These secretions mostly trap the pathogens and prevent them from reaching inside.

The cellular type includes some arrangements made to prevent microbe entry. For example, the wall of the blood vessels is tightly attached with each other ensuring that there is no gap hence preventing the entry of microbes.

The last type includes cytokines. The cytokines are a broad group of signaling proteins that take an important part in immunity. These molecules help in regulating the immune response.

The next article deals with the 6 mechanisms of innate immunity. Till that

HAPPY READING!!

There are about 1 trillion microbial species which constitutes about only 0.0001% of the entire species. One trillion itself is a huge number and they constitute the number of identified species only. Most of the microbes are packed inside the glaciers and is said that global warming which melts the glaciers can release them! The microbes can be broadly classified into 6:-

• Bacteria
• Archaea
• Fungi
• Protozoa
• Virus
• Algae

An important thing is that even though there are these many species of microbes, we do not get infected by them so often. To understand this it is trivial to know about the infection. Infection is defined as the invasion of the host’s body tissues by disease-causing microorganisms followed by their multiplication, colonization, reaction with the host, and release of toxic product metabolites. Infection is a complex process in which the harmful organisms enter into the host, finds a suitable and weak target place, establishes themselves well, multiples themselves, react with body cells, and release bad substances. The series of these events constitutes the prevalence of several diseases. The word ‘target site’ is very important since the microbe cannot establish themselves in any place in the human body. A clear-cut idea of this concept will be given in the next article.

Infection by a microbe can be best understood through relationships. A relationship is always exhibited between two organisms. There are three different kinds of relationships namely parasitism, commensalism, and symbiosis.

Commensalism– the relationship in which one of the organisms is benefitted and the other is neutral (neither harmed nor benefitted)

Symbiosis/mutualism– the relationship in which both the organisms help out with each other so that both are benefited

Parasitism– the relationship in which one organism is benefitted and the other is harmed. In this scenario, the harmed one is known as the host and the one causing the harm is the parasite.

The reason for which that all microbes don’t cause disease might be that some of them are cannot cause infection meaning that they are not parasitic. Under those circumstances, there are about 1500+ kinds of microorganisms that particularly target and infect human beings. If so, then we would have got around 1500+ diseases and that is not the case. So there is some inner force that protects/guards us against these microbes. This protective force present in our body is known as immunity.

Immunity is defined as the response generated by the local mammalian in response to the infection caused by the pathogenic microbes and their products (toxins).

As mentioned earlier, the microbe has to enter into the body in order to establish itself. In fact, this is the hardest part for the microorganisms and most of them fail to cross this stage. It is this immunity that prevents most of the microbes to enter the body and cause infections. The immunity identifies and destroys these microbes and prevents their infections.

The first step is known as recognition which is an important characteristic of the immune system. It is the ability that the immune system destroys the objects which are foreign or not present in the body (non-self) and do not affect the body cells (self). An error occurs in this and as a result, the immune system is unable to differentiate both and starts to destroy their own body cells. This condition is known as autoimmunity.

A brief introduction to immunity has been provided, the next article discusses the classification of immunity.

HAPPY LEARNING!!