Immune System and Human Health

Introduction

     Living organisms are exposed to various external or foreign substances and disease causing organisms like bacteria, viruses and fungi. Such organisms which can cause a disease are known as Pathogens. It is observed that some human beings are more prone to a certain disease and some others are immune to it.

Innate and Acquired Immunity

     The word Immunity, arises from the latin word 'Immunis' which means 'exempt' or 'freedom'. Immunity refers to all the mechanisms used by the body for protection from external agents which include microorganisms and their products, some food items, chemicals, drugs, pollen etc.

Innate (Non - specific) Immunity

     The human body continuously attempts to maintain homeostasis by counteracting harmful stimuli in the environment. These stimuli are mostly disease - causing organisms called Pathogens or their toxins.

Acquired Immunity

     Non-specific immunity is not specifically directed against a particular microbe. Specific immunity involves the production of a specific type of cell or specific molecule (antibody) to destroy a particular antigen. It is capable of recognising and selectively eliminating specific micro organisms.

Antigens

     An antigen is any chemical substance that, when introduced into the body, causes the body to produce specific antibodies, which can react with the antigen. Chemically a vast majority of antigens are proteins, nucleoproteins, lipo proteins etc. The entire bacterium or virus or components of microbes may act as an antigen. Bacterial toxins are antigenic.

Antibodies

     An antibody is a protein produced by the body in response to the presence of an antigen. Anti bodies belong to a group of proteins called globulins and they are also known as Immunoglobulins (Ig).

Active and Passive Immunity

     Active immunity develops as a result of the contact of an individual with pathogenic organisms or their products. They stimulate the body to produce antibodies in response to the antigens. The immunity thus produced is specific for a particular disease.

Activation of Adaptive Immunity

     Antigens are processed by antigen presenting cells like macrophages. The processed antigen is presented on the surface of these cells. A group of T-cells called T helper cells specifically interacts with the presented antigen and becomes activated.

Clonal Selection

     B and T lymphocytes have specific receptors on their surface. In B cells, this receptor is the antibody produced by that cell. When this receptor interacts with the antigenic determinant specific to it, the B lymphocyte becomes activated and divides to form a clone of cells.

Vaccination and Immunisation

     The principle of vaccination or immunisation is based on the property of 'memory' of the immune system. A vaccine is always given before the occurrence of the disease.

Blood Groups

     The surfaces of erythrocytes contain antigens called Agglutinogens. Two major blood group classifications - ABO grouping system and the Rh system - are based on the presence or absence of these proteins.

The Rh Factor

     The Rh system of blood classification is so named because it was first worked out in the blood of the Rhesus monkey. Like the ABO grouping, the Rh system is based on agglutinogens that lie on the surfaces of erythrocytes. Individuals whose erythrocytes have the Rh antigen are called Rh⁺. (Rh positive). Those who lack Rh antigen are called Rh^- (Rh negative).

Organ Transplants and Antibodies

     Organ transplantation is defined as the transfer of organs (like kidneys, heart liver etc) from one person to another.

Immune System Disorders

     The immune system protects the host from various infections. But an improper functioning of the immune system can cause discomfort, disease or even death.

Severe Combined Immuno Deficiency Syndrome (SCID)

     It is due to genetic defects. It is a disease of children, where both B-cells and T-cells are absent.

Acquired Immuno - Deficiency Syndrome (AIDS)

     It is a viral disease caused by the infection from a retrovirus, known as Human Immuno - deficiency Virus.

Summary

     The human body has elaborate mechanisms for protection against foreign bodies, germs and cancer cells.