The Immune Response of Mice to Serratia Marcescens LPS or Intact Bacteria

Abstract

Injection of adult mice with lipopolysaccharide (LPS) somatic antigen, or a heat-killed vaccine of Serratia marcescens resulted in rapid appearance of specific antibody-forming cells in the spleen, as well as other lymphoid tissues such as the mesenteric nodes and the thymus. Either immunogen in a dose of 50 µg resulted in a maximum cellular antibody response 3 to 5 days later; higher or lower doses resulted in a lesser response. Injection of 500 or 750 µg antigen gave the least response. In mice injected with the high doses of antigen, there was no compensatory increase in the number of antibody-forming cells in lymphoid organs other than the spleen. Regardless of antigen dose used or the time period after immunization antiglobulin facilitation yielded no evidence for additional plaque-forming cells. All concentrations of antigen gave a rapid increase in hemagglutinin and bacterial agglutinin titers, the vaccine giving the highest titers. Mice injected with 500 or 750 µg of either form of antigen had lower serum titers. Mice given the higher doses of either LPS or vaccine displayed a marked increase in the number of nonspecific antibody-forming cells to sheep erythrocytes. These results are viewed as evidence for development of immunologic tolerance to large doses of Serratia antigens, either vaccine or LPS. The toxicity of the antigenic preparations did not appear to be involved in the immunodepression. Both the antigenic state and dose markedly influenced the number of antibody-forming cells appearing after immunization.