The Lymph‐borne Cells of the Immune Response

The changes in the cell population in the efferent lymph from the popliteal node have been studied in unanæsthetized sheep given subcutaneous injections of various antigens into the lower part of the leg. The antibody content of the cells and of the lymph plasma has been measured during the immune responses which followed the injection of the antigens. Human serum globulin, chicken red cells and killed Salmonella typhi were the antigens used. The chicken red cells and Salmonella organisms were virtually all retained in the lymph node whereas human serum globulin was mostly recovered in the efferent lymph. With all the antigens, a characteristic cellular response occurred in the efferent lymph. Initially there was an increase in the output of mature lymphocytes followed by the appearance of primitive stem cells and finally plasma cells. Antibody was detected in the cells and lymph plasma in the experiments with particulate antigens and in the lymph in experiments with human serum globulin. When a second dose of particulate antigen was injected, the response was always shorter and more vigorous than after the first. There was little difference between the primary and secondary responses after human serum globulin. The cell population of afferent lymph was found to change in roughly the same way as that of efferent lymph when an antigen was injected into the leg. All the cell types which characterized the immune response in the efferent lymph were identified in the afferent lymph.