Ia-specific mixed leukocyte reactive T cell hybridomas: analysis of their specificity by using purified class II MHC molecules in synthetic membrane system.

This study was undertaken to determine the nature of the antigens recognized in allogeneic and syngeneic mixed leukocyte reactions (MLR). Specifically, we wished to determine whether Ia antigens alone were recognized by MLR-reactive T cells, or whether the specificity was determined by the corecognition of non-MHC antigens together with syngeneic or allogeneic Ia. To do this we used 11 T cell hybrids that were characterized as being specific for Iad and were tested their capacity to respond to isolated I-Ad or I-Ed that had been incorporated into liposomes and had bound to the surface of glass beads. Of nine alloreactive T cell hybrids (five I-Ad-and four I-Ed-specific), seven were shown to be responsive to the relevant isolated Ia antigen on glass beads. Also, two of two syngeneic I-Ad-specific T cell hybrids responded to I-Ad on the glass beads. One of the two alloreactive T cell hybrids that failed to respond to the relevant Ia antigen on glass beads was shown to be specific for an antigen in fetal calf serum (FCS) that was recognized in the context of the allo-Ia antigen (I-Ed), because when intact accessory cells were used, a response by this hybrid was only observed when FCS was present in the assay culture medium or when the accessory cells were pre-pulsed with FCS. The possible involvement of FCS antigens and non-Ia accessory cell antigens in the stimulation of the nine T cell hybrids that responded to isolated Ia on glass beads was evaluated. T cell hybrids that were grown and were tested in serum free medium were still capable of reacting to Ia on beads. The isolated Ia preparations used were greater than 90% pure, and their capacity to stimulate the T cell hybrids did not correlate with the degree of contamination with non-Ia proteins. We conclude from these studies that the majority of T cells that respond to allogeneic or syngeneic Ia bearing stimulator cells are specific for the Ia antigens themselves, and do not require the co-recognition of other non-Ia antigens; nor is there any requirement for Ia antigen processing for this recognition.

Tolerance to allotypic determinants induced by lymphoid cells from congenic mice bearing the allotype.

Mice of one allotype (Igb) were immunized against immunoglobulin from a congenic strain of mice bearing another allotype (Iga). This Igb anti-Iga response was profoundly suppressed by injecting lymphoid cells from congenic Iga mice but not by serum Iga. Suppression was specific, could be induced by congenic B cells but not histoincompatible lymphoid cells and depended both on the time of administration of cells relative to immunogenic challenge and to the number of cells injected. Unresponsiveness was more easily induced in neonates than adults. It is considered that tolerance to the allotype depends on the properties of the cells to which they are bound.

Production of antibodies to host IgG after transfer of histocompatible cells primed to host allotype.

A method is described to bring about endogenous production of antibodies to the Fc region of IgG. Mice of one allotype (Igb) were immunized against immunoglobulin from a congenic strain of mice bearing another allotype (Iga). The Iga-primed cells were transferred to congenic recipients bearing the Iga allotype and the production of anti-host allotype antibodies by the donor cells measured. Low levels of anti-host allotype antibodies were found in the sera of normal recipients but much greater amounts in recipients pretreated with cyclophosphamide. On ultracentrifugation some of these IgG antibodies sedimented at more than 7S probably because they were complexed with the IgG antigen. It is considered that thismodel may be of use in testing the effect of anti-Fc antibodies on joint inflammation.