CD8⁺ T Cells Negatively Regulate the Antibody Production from the Human PBMC being Immunized in Vitro with Antigen

Abstract

We have developed an in vitro immunization method of human peripheral blood mononuclear cells (PBMC) for generating human antigen-specific antibodies. We have previously demonstrated that the antibody production from the in vitro immunized PBMC was induced only when PBMCs was pretreated with Leu-LeuOMe (LLME), known to be toxic to monocytes and cytolytic cells. In this study, we tried to clarify the point of action of LLME in the in vitro immunization, and further to obtain the larger amount of human antibody with the increased specificity by simplifying the protocol. Firstly, we analyzed the population of PBMC treated with LLME by flowcytometry to investigate the effect of LLME on PBMC, indicating that CD8⁺ T cells decreased as compared to non-treated PBMC, while CD4⁺ T cells increased. Furthermore, we analyzed the cell population of in vitro immunized PBMC treated or not treated with LLME, demonstrating that CD8⁺ T cells decreased when using LLME-treated PBMC in in vitro immunization than when using non-treated PBMC. We have previously reported that LLME-treated PBMC, but not non-treated PBMC had an ability to produce antigen specific antibodies, suggesting that CD8⁺ T cells negatively regulate the antibody production from human PBMC being immunized in vitro. Actually, PBMC depleted of CD8⁺ T cells retained the ability to produce antigen specific antibody in the in vitro immunization similarly to the LLME-treated PBMC, although the non-treated PBMC did not produce the antibody. These results demonstrate that CD8⁺ T cells is a negative regulator for antibody production in the in vitro immunization of human PBMC.