IMMUNOLOGY SERIES-PART 5- INTRODUCTION TO THE IMMUNE CELLS

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).

neutrophil

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.

eosinophil

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!!