Under a title that may baffle some, Penn State immunologist Mizel and medical writer Jaret give a clear, up-to-date accounting of where we stand in immunological research. The only thing the experts knew, not long ago, was that there were white blood cells and antibodies. Then came cell culture techniques, unique strains of experimental animals, insights into complex diseases--and yet another medical revolution. Today the experts still talk of two basic types of immune defense: cellular immunity, mediated by a variety of T-cells and macrophages (the cells that devour invaders), and humoral, mediated by circulating protein molecules, the antibodies. But they are better able to describe the complex pattern of events each time an immune cell encounters a foreign invader--recognizable by the surface molecules, or antigens, it bears. Immediately upon recognition, the immune cell recruits macrophages that in turn release factors which stimulate the growth of more T-cells--and so on through a series of feedback loops and messages that eventually involve the nervous and endocrine systems as well. (E.g., the message may go out to raise body temperature, producing the fever that accompanies infection. Immune cells work more efficiently, it turns out, at higher temperature.) At a certain point, the system must be tuned down or turned off. This is a major role of T-suppressor cells; and in some conditions, such as AIDS, a wholesale loss of balance of immune cells may result. The authors let their tale unfold chronologically, explaining the pivotal experiments, arguments, and resolution of arguments. They explore the role of heredity in predisposing to certain diseases, the problem of cancer therapy and organ transplant (which entail major suppression of the immune system), and a number of diseases (multiple sclerosis, rheumatoid arthritis, diabetes) where the body's defenses are overactive or turn against the host tissue. In sum: a book that takes the reader from no knowledge to the intricacies of monoclonal antibody production--and makes it all seem logical.