The cellular basis of immunity

Abstract

Extract

The nature of the relationship between humoral immunity, characterised by the presence of serum antibodies, and delayed hypersensitivity, demonstrated by skin reactions, was a puzzle to early immunologists. The observation, made in 1945, that delayed hypersensitivity could be transferred from a sensitised to a normal animal by leucocytes but not by serum suggested that these two forms of immunity were separable. Soon after this observation was made a number of neonatal diseases associated with various immune deficiencies were described in children. The clinical features of these diseases and differences in their pathology also suggested a division between humoral and cellular immunity and, furthermore, indicated a role for the thymus in immunity. But it was the fortuitous discovery in 1956 that bursectomized chickens were unable to produce antibody but retained their cellular immunity that first established a definite relationship between a primary lymphoid organ and an immune function. Attention soon focussed on the avian thymus, another readily accessible primary lymphoid structure, and it was shown that thymectomy in chickens, and later in other species, suppressed cellular immunity while leaving antibody production largely intact. And so the important roles played by the primary lymphoid organs in directing the development of the immune system became appreciated and the concept of there being a division in immune activity accepted. It is now established that humoral immunity is a function of so-called B lymphocytes, while cell mediated immunity is a function of T lymphocytes.