THE DEMONSTRATION that immunoglobulin production was normal or minimally impaired in neonatally thymectomized animals1-3 has led to the speculation that man may have two distinct types of peripheral lymphoid tissue, each dependent upon a different primordial gut-associated lymphoid tissue ("central lymphoid tissue") for its development.4 The peripheral lymphoid tissue considered dependent on the thymus as the central lymphoid tissue ("thymic-dependent tissue") is the small lymphocyte which has an important role in delayed hypersensitivity and homograft rejection.3,5,6 The other peripheral lymphoid tissue consists of the large pyroninophilic lymphocytes and plasma cells which produce the immunoglobulins7 and is referred to as the immunoglobulin-producing system. The central lymphoid tissue of the immunoglobulin-producing system, has been definitely identified only in the chicken where the bursa of Fabricius, a hindgut lymphoid organ, is this central lymphoid tissue.3,8
These considerations have led to the suggestion that some of the immune-deficiency diseases