THE IMMUNE SYSTEM:
To understand what causes allergy, it is necessary to look at the workings of the immune system. One of the workers of the system is the B lymphocyte, a type of white blood cell which produces antibodies to each unwanted antigens. The antibodies act in several ways: they attack the antigen directly or protect the body’s cells from invasion by the antigen, or make the invader attractive to roaming scavenger cells called the macrophages, which then destroy it. The other major player in the immune system is the T lymphocyte, which in fact controls the whole immune system. A subpopulation of the T lymphocytes called ‘helper T cells’ promote the action of the various “arms” of the immune system and another, called ‘suppressor T cells’ help limit such immune reactions. Another type of T lymphocytes actually participates in killing the invading organisms and is called ‘killer cells’. The cell that comes into play first when a microbe invades our system is the ‘neutrophil’. Proteins called ‘complement’ help make the immune response much more effective and amplified by generating many new chemicals that attract immune system cells or otherwise help the process through a cascade with checks and balances.
Allergic reactions involve antibodies called IgE and cells that carry these molecules on their surface called mast cells (situated under the skin and mucus membranes) and basophils (that circulate in the blood). Chemicals stored in these cells are liberated and mediate the allergic reactions when appropriate antigen(s) make contact with the cells through the IgE antibody molecules. Allergic rhinitis and conjunctivitis (“hay fever”, “sinus” etc), asthma, hives, ‘atopic’ eczema and drug allergies are good examples of allergic disorders. When a severe allergic reaction occurs all over the body systems the condition is called ‘anaphylaxis’, a potentially life-threatening condition. Drug allergies and insect sting systemic reactions are some typical such reactions. Allergy immunotherapy (“allergy shots”) uses the relevant allergens in small but increasing quantities to desensitize the immune system and thus, eventually strong or complete protection can be obtained. Thus, a patient may get rid of most or all of the allergy in time and thus appear to be ‘cured’.
When immune system activity is directed against body’s own tissues, the condition(s) are called ‘autoimmune diseases’. Examples are “Lupus”, rheumatoid arthritis, some types of diabetes or thyroid diseases. The type of disease that is produced depends on the tissue that is attacked by the autoimmune reaction. Thus, in lupus where large quantities of antigen-antibody complexes float around and are filtered at some tissues, the damage occurs where such deposits exist. Thus, joints, pleura or pericardium (membranes lining the lungs and heart), kidneys or the skin are common targets. In rheumatoid arthritis the reaction is in the lining of the joints but many other tissues can also be involved, such as the lungs.
Immunodeficiency is a general term used for describing a variety of diseases where some part of the immune system is dysfunctional. Some of these diseases are very mild and selective but others are very severe and involve multiple arms of the immune system. In some only the antibody formation is affected but in others only the cells are defective. In yet another group the diseases show a combination of both cells and antibody defects. The most severe of these is called severe combined immunodeficiency; many of the immune system dysfunctions are due to abnormal genes and thus may be amenable to gene therapy. This is the future of Immunology where most of the genetic disorders may be prevented or cured by appropriate gene therapy.
If you have any questions or comments, you may e-mail P.K. Raghuprasad, M.D. at firstname.lastname@example.org
Disclaimer: The facts presented in this article and the views expressed are solely those of the author(s) and do not necessarily reflect the views of the Board of Directors or other members of West Texas Physicians Alliance.