Read this article to learn about some of the important immunological aspects in human health and disease.
Immunity in Health and Disease:
The prime function of immune system is to protect the host against the invading pathogens. The body tries its best to overcome various strategies of infectious agents (bacteria, viruses), and provides immunity.
Some of the important immunological aspects in human health and disease are briefly described.
In general, the immune system is self-tolerant i.e. not responsive to cells or proteins of self. Sometimes, for various reasons, the immune system fails to discriminate between self and non-self. As a consequence, the cells or tissues of the body are attacked. This phenomenon is referred to as autoimmunity and the diseases are regarded as autoimmune diseases. The antibodies produced to self-molecules are regarded as autoantibodies.
Some examples of autoimmune diseases are listed:
i. Insulin-dependent diabetes (pancreatic β-cell auto reactive T-cells and antibodies).
ii. Rheumatoid arthritis (antibodies against proteins present in joints).
iii. Myasthenia gravis (acetylcholine receptor autoantibodies).
iv. Autoimmune hemolytic anemia (erythrocyte autoantibodies).
Mechanism of autoimmunity:
It is widely accepted that autoimmunity generally occurs as a consequence of body’s response against bacterial, viral or any foreign antigen. Some of the epitopes of foreign antigens are similar (homologous) to epitopes present on certain host proteins. This results in cross reaction of antigens and antibodies which may lead to autoimmune diseases.
The phenomenon of transfer of cells, tissues or organs from one site to another (in the same organism, auto graft or from another organism allograft) is regarded as organ transplantation. In case of humans, majority of organ transplantations are allografts (between two individuals). The term xenograft is used if tissues/ organs are transferred from one species to another e.g. from pig to man
Organ transplantation is associated with immunological complications, and tissue rejection. This is because the host body responds to the transplanted tissue in a similar way as if it were an invading foreign organism. Major histocompatibility complex (MHC) is primarily involved in allograft rejection. This is due to the fact that MHC proteins are unique to each individual, and the immune system responds promptly to foreign MHCs. Organ transplantation between closely related family members is preferred, since their MHCs are also likely to be closely related. And major immunological complications can be averted.
Growth of tumors is often associated with the formation novel antigens. These tumor antigens (also referred to as oncofetal antigens e.g. α-fetoprotein) are recognized as non-self by the immune systems. However, tumors have developed several mechanisms to evade immune responses.
Acquired immunodeficiency syndrome (AIDS), caused by human immunodeficiency virus, and is characterized by immunosuppression, secondary neo-plasma and neurological manifestations. AIDS primarily affects the cell-mediated immune system which protects the body from intracellular parasites such as viruses, and bacteria. Most of the immunodeficiency symptoms of AIDS are associated with a reduction in CD4 (cluster determinant antigen 4) cells.