THE IMMUNE SYSTEM AND DISEASE RESISTANCE

By W. Jean Dodds, DVM
Hemopet, 938 Stanford Street,
Santa Monica, California 90403

Reprinted with permission from Dr. W. Jean Dodds

 This article discusses the essential role of the immune system in maintaining the body's overall general health and resistance to disease. The focus will be on environmental factors or events which may cause or trigger immune dysfunction leading to either immune deficiency or immune stimulation (reactive or autoimmunity). Related to these events is the development of cancer which is a disruption of cell growth control.

Overview of the Immune System

Immune competence is provided and maintained by two cellular systems which involve lymphocytes. Lymphocytes are cells produced by the body's primary (bone marrow and thymus) and secondary (lymph nodes and spleen) lymphatic organs. They are descendants of the bone marrow's pool of stem cells, and produce a circulating or humoral immune system derived from B-cells (bursa-dependent or bone marrow derived), and a cellular or cell-mediated immune system that derives from T-cells (thymus dependent).

B-Cell Immunity

B-cell immunity includes the circulating antibodies or immunoglobulins such as IgG, IgM, IgA, IgD, and IgE. These antibodies provide an important defense mechanism against disease in healthy individuals but can become hyperactive or hypoactive in a variety of disease states. Hyperactive or increased levels of immunoglobulins can occur in two ways: acutely, as a reaction to disease or inflammatory insult ("acute phase" reaction); or chronically, as in autoimmune or immune-mediated diseases, chronic infections, and certain types of bone marrow and organ cancers. Hypoactive or decreased levels of immunoglobulins can result from rare genetically based immunodeficiency states such as agammaglobulinemia or hypogammaglobulinemia, and from the immune suppression associated with chronic viral, bacterial, or parasitic infection, cancers, aging, malnutrition, drugs, toxins, pregnancy, lactation, and stress.

T-cell Immunity

T-cell, or cell-mediated immunity is the cellular mechanism whereby T-cells act as coordinators and effectors of the immune system. Cell-mediated immunity involves the lymph nodes, thymus, spleen, intestine (gut-associated lymphoid tissue), tonsils, and a mucosal secretory immunity conveyed by IgA.