Previously unrecognized functions of the spleen: development and maintenance of immune competence and regulation

To examine the influence of the spleen on the development and function of the immune system, the effects of the inborn asplenia in Dh/+ mice were studied and compared with those of neonatal and postnatal splenectomies. The antibody responses to particulate and soluble antigens in Dh/+ mice were weaker than those in normal controls. This was correlated with the inability of Dh/+ T-lymphocytes to cooperate with B cells in cell-transfer experiments. A defective helper function was also found in T-cells of neonatally splenectomized mice, but it could be restored partly by delaying the removal of spleen until 6 days after birth and totally by infusing autologous spleen cells immediately after splenectomy. By contrast, transfer of spleen cells to Dh/+ mice did not restore the helper function of their T-lymphocytes. Unlike their defective humoral immunity, the cellular immune responses of Dh/+ mice are normal as expressed in their ability to reject foreign grafts and to be contact-sensitized by chemicals. Thus, the presence of the spleen at birth is essential for the development of helper T-cells but not cytotoxic or effector T-cells. Furthermore, evidence is reviewed for the splenic influence on the capacity of other lymphoid organs to trap particulate antigens and for the role of the spleen in the maturation of suppressor T-cells throughout the life span.