Relationship between antigenic stimulation and increased splenic peroxidase levels during the immune response

Immunization of mice with either soluble or particulate antigens induced a marked increase in peroxidase activity of spleen cell homogenates. Animals immunized with sheep erythrocytes showed maximum splenic peroxidase activity at 2 days. By the 4th day after immunization, when the hemolytic antibody plaque-forming cell response was maximal, peroxidase activity returned to normal levels. Increased splenic peroxidase activity also occurred in mice immunized with rabbit erythrocytes, as well as with rabbit serum or bovine serum albumin. No change in splenic peroxidase activity occurred in mice injected with syngeneic mouse erythrocytes or serum. Both glass-adherent spleen cell populations, morphologically consisting of 90 to 95% macrophages, as well as nonadherent cells, consisting of more than 90% lymphocytes by the same criteria, showed peroxidase activity. Immunization of mice with sheep erythrocytes resulted in an intracellular redistribution of the peroxidase activity among several distinct subcellular fractions prepared by differential centrifugation. Maximum redistribution occurred with granule-associated enzyme activity. A possible relationship between peroxidase activity with functional activity of lymphocytes and macrophages during humor immune responses seemed likely.