It is now well established that compatibility for the t t L -A antigens between donor and host siblings is generally associated with prolonged excellent function of renal allografts (1-6). Although it may not be possible to identify all of the possible antigens of both segregating series in transplant pairs, nonreactive mixed lymphocyte cultures (MLC) 1 have proven to be excellent predictors of HL-A compatibility and graft function.Controversy remains, however, as to what criteria of compatibility determined either by serologic typing (1 6) for H L -A antigens or degree of stimulation in MLC (1, 2, 7-13) can be relied upon to predict the next level of comparatively good transplant success. In this regard, Bach and others (2, 14-16) have stressed that within families donor-host compatibility for one allele is usually associated with intermediate stimulation in MLC as compared with two-allele compatibility or disparity. Seigler et al. (7), however, have noted rather remarkable overlap between the MLC responses between one-and two-allele mismatched cell donors.We have noted the same variability, but now report that a subgroup with low MLC stimulation may be distinguished bv the fact that the donor and host pair share one allele plus one antigen of the second unmatched allele as determined by lymphocytotoxicity testing for HL-A antigens.
Materials and Methods16 families with at least four members were included in which genotyping for two segregating series of the HL-A locus was established on the basis of positive identity of at least three and sometimes four antigens. Serologic typing and MLC tests were all performed as a part of the work-up of one family member as a potential renal transplant recipient. The potential *Supported by National Institutes of Health grant AI-09716-01 and the Veterans Administration.1 Abbreviations used in this paper: