IMMUNOLOGY SERIES- PART 8- INFLAMMATION

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.

Mediator nameIt’s effect
Bradykinin, histamine, serotoninIncrease permeability
ProstaglandinDecreases blood pressure
CytokinesProduce fever
Toxic metabolitesDamage tissue

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:-

immunity in the skin
  • 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!!!