Immunodeficiency states relevant to infection

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The importance of immune mechanisms in resistance to infection is most apparent in persons with deficient immunity. Although immunodeficiency states are relatively uncommon, the study of patients with such defects has led to significant insights into the functioning of the normal immune system. Moreover, from a practical point of view, it is occasionally necessary to consider the differential diagnosis of immune deficiency in patients with repeated infections, or in patients with unusual infections. To approach an evaluation rationally, it is helpful to have some broad concepts about the organization of the immune system.

This paper presents a simple review of the functional and morphologic organization of the immune system, a discussion of the differential diagnosis of immunodeficiency states, and an orderly approach to the examination of patients suspected of having immune deficiency.

Organization of the immune system

Since the early work of Miller1 in clarifying the role of the thymus gland and that of Cooper et al2 in defining the function of the bursa of Fabricius in chickens, the binary structure of the immune system has become widely accepted. Primordial immunocytes from bone marrow mature along one of two pathways under the influence of the two central lymphoid organs, the thymus gland and the bursa or bursal equivalent (Fig. 1).

The thymic influence leads to generation of the T-cell population, which includes the great majority of cells in the thymus gland itself, cells in the “thymic-dependent” areas of peripheral lymph nodes (paracortical areas), and a circulating population of small lymphocytes found. . .



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