Expression of Ia in mouse kidney.

Expression of Ia antigens in mouse kidney was studied by absorption of diluted anti-Ia sera with crude suspensions of kidney issue. Specific absorption of anti-Ia activity was seen for all Ia specificities tested: Ia.1,2, Ia.3, Ia.4,5,12, Ia.7, Ia.8, Ia.9, Ia.15, and Ia.16. Certain polyspecific antisera (against the I-Ak products Ia.1,2,3,15) were more difficult to absorb than oligo-specific antisera against other Ia specificities (e.g., Ia.7 and Ia.9). This observation may indicate that polyspecific sera are less absorbable by limited numbers of antigenic sites because of steric hindrance, although differences in the extent of antigen expression in kidney have not been excluded. Ia absorption could be demonstrated either in microcytotoxicity or in 51Cr release assays. Both mechanically disrupted and enzyme-disrupted kidney tissue suspensions absorbed Ia specifically, although the former method was used routinely. As estimated from the efficiency of absorption, the amount of Ia in kidney was small, about 2 to 5% of that in spleen. One kidney was equivalent in absorptive capacity to about 3 X 10(6) splenocytes, and to greater than 3 X 10(6) buffy coat cells. Comparisons of the rates of absorption indicated that the amount of Ia in kidney was less than the amount of an H-2K or D alloantigen. Ia was expressed in kidney in an immunogenic form, since animals immunized repeatedly with I region-incompatible kidney tissue produced anti-Ia antibodies. Thus, Ia antigens are expressed in and are immunogenic in mouse kidney and can be studied by conventional serological techniques.