DIFFERENTIAL REGULATION OF B7 MESSENGER-RNA IN ENTEROCYTES AND LYMPHOID-CELLS

To investigate the molecular details of antigen presentation by cells of lymphoid or epithelial origin, we compared B7 mRNA regulation in in testinal epithelium with that in spleen, since both cell types express class II major histocompatibility complex (MHC) and present antigen. As measured by cDNA amplification using sequence-specific primers, I-A beta mRNA content was found to be similar in mouse full-thickness smal l intestine, isolated intestinal epithelial cells and spleen. However, in contrast to I-Abeta, B7 mRNA intestinal epithelial cell content wa s markedly lower than in spleen and whole small bowel; cardiac RNA was negative for both sequences. Administration of intraperitoneal interf eron-gamma (IFN-gamma) (10(5) U daily for 2 days) to adult mice result ed in an increase in I-Abeta mRNA in epithelial cells, but did not alt er levels of B7 mRNA. In addition, exposure of the IEC-6 rat cell line to the IFN-7 resulted in a dose-dependent increase in I-Abeta mRNA wi thout altering levels of B7 mRNA. Thus, an apparent dichotomy exists i n regulation of B7 and I-Abeta gene expression in rodent intestinal ep ithelial cells. Since maximal T-cell response to splenocytes depends o n B7, the absence of B7 mRNA in intestinal epithelium may be a factor in determining why antigen-presenting enterocytes normally do not elic it damaging T-cell proliferative responses.