EXPRESSION OF Ia IN MOUSE KIDNEY

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Abstract
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 oligospecific antisera against other Ia specificities (e.g., Ia.7 and Ia.9). Polyspecific sera may be less absorbable by limited numbers of antigenic sites because of steric hindrance, although differences in the antigen expression extent in kidney were not excluded. Ia absorption could be demonstrated in microcytotoxicity or in 51Cr release assays. 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 Ia amount in kidney was small, .apprx. 2-5% of that in spleen. One kidney was equivalent in absorptive capacity to .apprx. 3 .times. 106 splenocytes and to greater than 3 .times. 106 buffy coat cells. Comparisons of the absorption rates 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. Ia antigens are expressed in and are immunogenic in mouse kidney and can be studied by conventional serological techniques.