V. Fundamental Changes in the Physiological Characteristics of Virgin Thymus-independent ("b") Lymphocytes and "b" Memory Cells* by Samuel Strober:~

Thymus-dependent, helper cells ("T" lymphocytes) 1 and thymus-independent, antibody-forming precursor cells ("B" lymphocytes) cooperate in the initiation of the primary antibody response of rodents to a variety of antigens (1-3). Both cell lines also cooperate in the initiation of the secondary antibody response, and both carry immunological memory (4, 5). Recent cell transfer studies indicate that B memory cells determine the changes in the proportion of immunoglobulin classes and affinity of antibodies produced in the secondary response (6-8). These changes suggest that B memory cells are not derived by a simple expansion of unprimed B lymphocytes, but rather by heterogeneous expansion of subpopulations of unprimed B lymphocytes or by a qualitative change in immunological function. On the other hand, the carriage of immunological memory by T lymphocytes could be explained by a homogeneous expansion of unprimed T cells. Miller et al. (5) and Mitchell et al. (4) have shown that both primed and unprimed T lymphocytes are able to cooperate with primed B lymphocytes in the adoptive secondary antibody response of mice to fowl gamma globulin and sheep red blood cells (SRBC), respectively. Approximately, ten times as many unprimed as primed T lymphocytes were required to restore responses of equal magnitude (4, 5). However, the adoptive secondary response to either antigen could not be restored by a combination of primed T lymphocytes and large numbers of unprimed B lymphocytes (4, 5). This suggests that a fundamental change in the immunological function of B but not T lymphocytes occurs after priming.