Immune defenses can be low for several reasons: There can be primary defects innate to the immune system and secondary defects acquired in the course of one’s life because of contracting diseases.

One of the most serious of these diseases is AIDS, the fearsome pandemic that exploded during the 1980’s. It is caused by the human immunodeficiency virus (HIV), which can strike at the heart of the immune system, progressively destroying a particular class of lymphocytes. An extremely important part of the individual’s defenses is thus incapacitated. After that, infections recur and are never completely eradicated. In fact, they get worse, and the body is left without the means for defending itself.

Fortunately, not all immunologic deficits are of such a serious nature. Many immune deficiency diseases involve a minor defect in the production of one kind of antibody. Usually, a course of injections that would stimulate the production of antibodies can remedy the problem.