The macrophage response in mice after primary and secondary immunization with sheep red blood cells.

A primary and a secondary immune response to sheep red blood cells (SRBC) was evoked in mice by intraperitoneal injection of the antigen. Macrophage proliferation and migration as well as induction of the lysosomal enzyme acid phosphatase in macrophages were assessed along with lymphocyte proliferation. The proliferative responses were evaluated by 3H-thymidine labelling (autoradiography). The secondary response elicited a faster and stronger lymphocyte proliferation than the primary response. This pattern was not seen to apply to the macrophages where the highest proliferative rate was found in connection with the primary response. The macrophages acquired an increased content of acid phosphatase during both types of responses, but the significantly highest level was reached in the secondary response. Large numbers of monocytes migrated into the peritoneal cavity during the first day after immunization. However, macrophage proliferation took place in resident as well as in immigrant cells.