Studies on the Specificity of the Cellular Infiltrate in Delayed Hypersensitivity Reactions

Abstract

Summary In actively immunized guinea pigs given H3 thymidine during the 2 days preceding skin testing, delayed hypersensitivity reactions contained a high percentage (87 to 92%) of labeled mononuclear cells. Experiments were performed in which two noncross-reacting sensitivity systems were transferred by lymph node cells to single recipient guinea pigs, with the donors sensitized to one of the antigens having received H3 thymidine, whereas the donors to the other system supplied unlabeled cells. Delayed sensitivity reactions elicited by each of the antigens at separate sites in these recipients were found to contain comparable numbers of labeled cells. The average percentage of labeled mononuclear cells in the infiltrate was 4%. Experiments were performed in which delayed sensitivity was transferred by unlabeled lymph node cells from actively immunized donors into nonimmunized guinea pigs which had received H3 thymidine during the 2 days preceding transfer. Delayed sensitivity reactions in these recipients contained a high percentage of labeled mononuclear cells (68 to 91%). The observations indicate that the great majority of mononuclear cells which comprise the infiltrate in delayed sensitivity reactions are not specifically sensitized cells. In addition, the findings show that almost all of the mononuclear cells comprising the infiltrate are cells which have recently proliferated. The observations fail to provide evidence for the specific attraction of sensitized cells to the antigen. It is suggested that the delayed hypersensitivity reaction is initiated by the random arrival of a small number of specifically sensitized cells at the antigen site.