The effect of erythrocyte antigen structure on requirement for T cells.

The induction in mice of a humoral immune response to intact sheep erythrocytes, both in vivo and in vitro, requires participation of thymus-derived (T) lymphocytes. In an in vitro system, spleen cells from both neonatally thymectomized and adult thymectomized irradiated bone marrow protected mice were successfully immunized, using washed sonicated sheep erythrocyte membrane fragments as antigen. This obviation of the requirement of T lymphocytes in the immune response, coupled with previous work on macrophage independence, indicates that sonicated membrane fragments were capable of directly immunizing bone marrow-derived (B) lymphocytes in vitro. These results further confirm the signal importance of antigenic structure in determining the cellular requirements for an immunological response; whereas antigens of particulate or monomeric form require the presence of both T cells and macrophages, polymeric antigens of intermediate size such as polymerized flagellin and sonicated sheep erythrocyte membranes require neither of these accessory cells. The results caution against the use of erythrocytes as models of thymus-dependent antigens. The data further suggest that reports of late antibody responses of relatively normal magnitude in thymectomized animals given larger doses of heterologous erythrocytes may have been due to direct immunization of B lymphocytes by degraded erythrocyte antigen.