Previous studies have shown that the peptides obtained from accessory cell and B-cell Ta molecules are identical but that the a chains of B-cell Ia molecules are more extensively sialylated than those of accessory cells. The present studies were designed to determine whether this glycosylation difference can account for the functional difference in the capacity of the two cell types to activate alloreactive T cells. The experimental data show that normal resting B cells lack the capacity to induce DNA synthesis or differentiation in alloreactive T cells. T cells do recognize polymorphisms in B-cell Ia molecules, however, because they can be specifically primed for a subsequent proliferative stimulus of the same haplotype. The mitogenic signal for T cells is delivered by either allogeneic accessory cells or neuraminidase-treated B cells. Therefore, the T-cell receptor(s) may contain a site specific for the nonpolymorphic asialocarbohydrate moiety on the a chains of accessory cell Ia molecules.
The possibility was investigated that Ir genes regulate the function of cells other than T or B cells in the primary IgM responses to the synthetic antigens trinitrophenylated poly-L-(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys [TNP-(T,G)-A--L]and trinitrophenylated poly-,-(His,Glu)-poly-D, L-Ala--poly-L-Lys [TNP-(H,G)-A--L]. The primary responses of (B10 × B10.A)F(1) spleen cells to both antigens were abrogated by Sephadex G-10 passage, and restored by the addition of spleen adherent cells. The cell type in the spleen adherent cell population active in reconstituting the responses to TNP-(T,G)-A--L and TNP-(H,G)-A--L was a non-T, non-B, radiation-resistant, glass-adherent spleen cell. The responses of Sephadex G-10-passed (responder x nonresponder)F(1) spleen cells to TNP-(T,G)-A--L or TNP-(H,G)-A--L were reconstituted by spleen adherent cells from only responder strains. Spleen adherent cells from F(1) mice reconstituted the responses to both antigens. Spleen adherent cells from each of the strains tested reconstituted the non- Ir gene-controlled response to a third antigen, TNP-keyhole limpet hemocyanin. The inability of spleen adherent cells from nonresponder strains to reconstitute the responses to either TNP-(T,G)-A--L or TNP-(H,G)-A--L was not a result of active suppression induced by the presence of nonresponder adherent cells, since a mixture of responder and nonresponder spleen adherent cells reconstituted the responses to both antigens. The use of spleen adherent cells from recombinant strains demonstrated that the autosomal dominant genes controlling the ability of spleen adherent cells to function as accessory cells in the responses to TNP-(T,G)-A--L and TNP-(H,G)-A--L are located in the K or I-A regions of the responder H-2 complex, the same region(s) of H-2 as the Ir genes controlling overall in vitro and in vivo responsiveness to these antigens.
We have introduced the class II E alpha d gene into (C57BL/6 X SJL) F2 mice which do not express their endogenous E alpha gene. The mRNA expression of the E alpha d gene shows the same tissue distribution as the endogenous class II genes except in the case of one mouse, which carried 19 copies of the E alpha d gene. In this mouse expression of E alpha d mRNA was seen in all tissues tested. Expression of the transgene was induced by gamma‐interferon in isolated macrophages from the transgenic mice. In addition, fluorescence activated cell sorter (FACS) analysis, mixed lymphocyte response and antigen‐presentation experiments showed that the product of the transferred gene is expressed on the cell surface and functions as a major histocompatibility complex restriction element. Transmission of the gene occurred only with female transgenic mice, all males were infertile or did not transmit the gene, suggesting an effect of the transferred DNA sequence on male reproductive function.
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