Ontogeny of the Immune Response

Abstract

Summary Germfree, colostrum-deprived piglets obtained by hysterectomy 3 to 5 days prior to term were free of detectable immunoglobulins in their sera and appeared to be “immunologically virgin.” This model was used, therefore, to determine whether “natural” antibodies are required for induction of antibody formation and for the phagocytic function of the reticuloendothelial system (RES). Within 2 hr, 99.9% of actinophage MSP-2, 85% of keyhole limpet hemocyanin (KLH) and 50% of bovine serum albumin (BSA) were eliminated from the blood of these “immunologically virgin” animals. After 48 hr the rate of clearance of MSP-2 increased markedly, indicating immune elimination. This correlated with the time of the onset of the true primary immune response involving 19 S γG. Comparable immune elimination within the same period was not observed with soluble BSA and KLH. With the more antigenic particulate phage, the lag or inductive period in the true primary immune response was probably less than 36 hr. These results indicate that the initial elimination of antigen in this model is an innate physiologic mechanism independent of antibodies. Passively immunized piglets eliminated antigen rapidly indicating that specific antibody assists and enhances the function of the RES. In these “immunologically virgin” animals, the soluble antigens BSA and KLH were eliminated slowly and gave a delayed immune response compared to the rapidly cleared and highly antigenic particulate actinophage. It is suggested that phagocytability and digestability of antigen influence antigenicity.