In vitro enhancement of antibody responses by Tδ cells expressing IgD receptors

Previous in vivo studies have shown that murine T cells induced to express receptors specific for IgD (IgD-R) have humoral immunoaugmenting properties with respect to both primary and secondary antibody responses to various antigens. Such murine IgD-R⁺ T cells (Tδ cells) belong to the CD4⁺ T cell population in contrast with human Tδ cells which also include CD8⁺ cells. The purpose of these studies was to develop an in vitro assay system to examine the mechanism by which Tδ cells facilitate enhanced antibody responses. Our studies demonstrate that B cell responses to both soluble and particulate antigens can, indeed, be enhanced in vitro by coculture with T cells previously induced to express IgD-R. This in vitro effect requires cognate interaction between T and B cells and is dependent on the presence of adherent cells or IL-1. T cell priming with antigen, while not a prerequisite, was found to result in more effective Tδ-B cell interactions compared with naive Tδ cells. Finally, evidence was obtained in support of an adhesion-mediated Tδ-B cell interaction since the immunoaugmenting properties of T cells expressing IgD-R are completely blocked by the addition of very low doses of monomeric IgD to the cultures.