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Immunologic Tolerance to Escherichia Coli Somatic Antigen Assessed by Bacteriolytic and Hemolytic Plaque Assays^{1 ,2}

From the Departments of Microbiology, Albert Einstein Medical Center and Temple University Medical School, Philadelphia, Penna.

Abstract

Immunologic tolerance to the somatic antigen of E. coli 0127:B8 was induced in neonatal mice by multiple injections with a lipopolysaccharide (LPS) antigen during the first weeks of life. The immune response of neonatally treated animals, as well as that of non-treated control mice, was assessed by two different kinds of immunoplaque assays: 1) direct bacteriolysis of viable E. coli in agar gel, and 2) hemolysis of sheep erythrocytes coated with specific antigen. Mice treated with differing amounts of LPS, and a variety of injection schedules, developed a marked tolerance as assessed by the indirect hemolytic plaque assay, as well as by serum hemolysin and hemagglutination tests. In contrast, significant numbers of plaque-forming cells were detected in spleens of neonatally treated mice when the direct bacteriolytic assay was used. Similarly, there were higher bacterial agglutinin titers in the sera of these animals. Larger numbers of antibody-forming cells were detected by the hemolytic assay in the spleens of control mice after challenge immunization than in neonatally treated animals. Significant numbers of bacteriolytic plaque-forming cells were present in the spleens of "tolerant" animals, in contrast to the marked suppression of hemolytic cells. These findings suggest that tolerance to bacterial antigens as complex as the somatic extracts of E. coli results in tolerance to "major" antigenic determinants and a concomitant immunity to some but not all of the "minor" antigens which fail to coat onto carrier erythrocytes.

Footnotes

¹ Supported in part by research grants from the National Science Foundation (GB 6251).

² Presented, in part, at the 68th Annual Meeting, American Society for Microbiology, Detroit, Michigan, May 1968.

³ Post-doctoral fellow, National Institutes of Allergy and Infectious Diseases (No. 1-F2-A1-38012-01).