Immune Reaction

 Immune Reaction

PKGhatak, MD

While reading any medical journal one usually encounters various descriptions of tissue response to injuries, infections, and illnesses, described as reactions. Immune reactions are the body's attempts to stamp out or control infection, cancer and diseases in an orderly fashion by the use of specialized cells and biochemical molecules.

Our body is pre-programmed to repose by a set pattern of actions called Innate or inherited immune reaction. And by a separate set of actions, from experience gained from encounters with the offending agents, called Acquired Immune reaction.

Innate reaction.

The skin, surface layer of the nose, mouth, GI, Respiratory and Genitourinary tracts are the physical barriers to invaders. Once that defense is breached, then the responsibilities fall on the surveillance cells for finding the invaders or cancer cells. These immune cells are Dendritic cells They recognize the molecular patterns of the invaders' surface membrane, and they attach themselves cells attach to it, like a key fits a lock and release the chemicals, called Cytokines. In repose to cytokines, neutrophils, monocytes, eosinophils, phagocytes and complements gather at the site. And a series of actions and reactions take place in the local area resulting in increased blood flow, redness, swelling, temperature elevation and temporary loss of function.

The complement pathway of action is described as the Classical Pathway. Other pathways are also present, these are Alternate Pathway, and Mannose-Lectin Pathway. These pathways are activated by yeasts, viruses and certain bacteria.

The end result of this action is that the invasion is checked, the invaders are paralyzed and eaten alive by the macrophages and the dead bodies are removed from the area in order for healing to take place.

Adaptive Immune Reaction:

Acquisition of adaptive immunity is a learned process. During the first encounter with a pathogen a signature part of the pathogen - usually, a protein molecule called antigen is recognized by the dendritic cells and the information is passed in succession to lymphocytes of various designations like B-cells, T-cells and ultimately to antibody producing B-lymphocytes. B-cells produce immunoglobulin, specific for that antigen, which combines with that antigen and neutralizes the pathogen. This antigen remains in memory in a subset of B -cells in the regional lymph nodes, but the memory is short-lived. Some memory B-cells move to the bone marrow and there retain memory permanently. 

Like innate immunity, adaptive immunity also consists of a cellular component and a Humoral component.

Adaptive immunity has a wide range of actions on pathogens and can be obtained in various ways.

Classification of adaptive immunity.

A. Natural

1. Passive immunity. A developing child in the mother's womb gets antibodies from the mother's blood via the placenta, and in some cases also from breast milk.

2. Active immunity is acquired from prior infection by that pathogen.

B. Artificial.

1. Active. Use of vaccine to generate antibodies, which protects an individual for a period of time depending on the nature of the pathogen.

2. Passive. By given IV antibodies, obtained from recovered patients or generated in animals by inoculating the animal, or obtained in the laboratory by the cell culture methods.

Abnormal Immune reaction.

Not every attempt to generate an adequate number of immune cells and antibodies against a pathogen will go smoothly. In some cases, the defect may lie in abnormal genes in a family or gene mutation of the individual. The response may be either excessive called Hypersensitivity reactions or cross reacts with normal body cells called Autoimmune diseases.

A. Hypersensitivity.

1. Immediate. The reaction happens within 24 hours after exposure to an allergen (pathogen).

Immediate hypersensitivity is of 3 different types.

Type I hypersensitivity reaction.

Also known as Immediate immune reaction, Allergy, Anaphylaxis and Atopy. The body produces Immunoglobulin E (IgE) instead of Immunoglobulin M or G (IgM, IgG). The circulation IgE binds with Mast cell receptors. When sensitized mast cells encounter the same pathogen again (like pollen, bee stings, peanuts, etc.), the encounter causes the mast cell to release the preformed granules containing Histamine, and other enzymes at the site and the consequence of that is the dilated blood vessels, fluid escaping locally. Nasal discharge, cough, parochialism, and itching is produced depending on whether it occurs in the nose, lungs, or skin respectively.

Anaphylaxis.

Anaphylaxis is an excessive amount of cytokines released in a minute after exposure resulting in a drop in blood pressure, severe tightness in the chest, low blood oxygen and cardiovascular collapse.

Type II hypersensitivity reaction.

In type II reaction, the IgM and IgG antibodies are involved. Examples of clinical conditions are Acquired hemolytic anemia, Rheumatic heart disease, Good Posture syndrome, Myasthenia gravis, Pemphigus Vulgaris, etc. 

Type III hypersensitive reaction.

Type III reaction is known as Immune complex mediated reactions. Here IgG, complement and neutrophils are involved. Clinical examples are Serum sickness, Rheumatoid arthritis, Lupus erythematosus, Glomerulonephritis, Hypersensitive pneumonitis, etc.

B. Delayed reaction.

The delayed hypersensitive reaction is also known as Type IV reaction, Cytotoxic or Cell mediated hypersensitive reaction. The reaction starts at 48 to 72 hours after exposure.

In type IV reaction, Thymic Th1 and Th17 cells are participants. Clinical examples are Contact dermatitis, poison ivy, Chronic transplant rejection, Multiple sclerosis, Celiac disease, Hashimoto thyroiditis, Granuloma annuaries, etc.

Autoimmune disease.

The acquisition of knowledge by the immune cells that are foreign is gained in the developing T cells in the thymus in the developing embryo, and the learning process continues at a slow pace during the rest of life.

                                         [https://humihealth.blogspot.com/2021/08/thymus.html]

The mutated genes, either inherited or acquired gene mutation, result in misdirected immune attacks against its own normal tissue or organ.

Clinical examples are Crohn's disease, Acquired hemophiliac anemia, Aplastic anemia, Thrombotic thrombocytopenic purpura (TTP), SLE, Multiple sclerosis, Rheumatoid arthritis, Type1 Diabetes mellitus. Pernicious anemia, etc.

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