Immunogenic presentation of an immunoglobulin "tolerogen" requires interleukin 2

Previously it has been reported that hapten-specific B cell unresponsiveness could be elicited by macrophages pulsed with the tolerogen deaggregated fluoresceinated sheep gamma globulin (FL-SGG; R. P. Phipps and D. W. Scott, J. Immunol. 1983. 131:2122). In contrast, FL-SGG-pulsed P388AD.2, a lymphoid dendritic cell-like tumor line, presents this signal as an immunogenic one leading to augmented anti-FL antibody responses. In the present study, we examined the role of T cells and their secreted lymphokines in the immunogenic presentation of FL-SGG by P388AD.2. Lymphocytes and FL-SGG-pulsed P388AD.2 form large clusters in vitro. In order to examine whether the clustered lymphocytes were responsible for the augmented antibody responses, cultures of P388AD.2 and lymphocytes were separated into P388AD.2 adherent (clustered) and nonadherent fractions. Interestingly, the clustered fraction was entirely responsible for the augmented responses and contained Ly-1+ T cells and B cells primed by FL-SGG on P388AD.2. Moreover, a requirement for T cells in the presentation of a normally tolerogenic signal as an immunogenic one was demonstrated as responses of T-depleted spleen cells could be reconstituted by addition of normal T cells or by an autoreactive T cells clone. Furthermore, the requirement for T cells could be bypassed using supernatant from concanavalin A-stimulated spleen cells or by culture supernatant from AOFS, an IL 2-secreting T cell hybridoma. This suggested that a cognate interaction between T and B cells was not required to induce B cell priming and the augmented anti-FL antibody responses. Further studies revealed that doses of recombinant IL 2 greater than 12.5 units/ml, in conjunction with FL-SGG-pulsed P388AD.2, replaced the need for T cells. Overall, our data suggest that one mechanism of presentation of FL-SGG in an immunogenic fashion involves T cell secretion of IL2 by autoreactive T cells triggered by close association with P388AD.2.