Quantitation of HLA-D differences.

The predictability of MLC non-reactivity by HTC typing was tested in a single checkerboard experiment which involved 39 unrelated individuals belonging to 12 different groups of HLA-D identical phenotypes. The strength of one-way MLC reactions in all possible responder-stimulator combinations (39 X 39) was quantitated by the Linear Clustering Analysis Program. Individuals who, by HTC typing, were identical for two HLA-D antigens gave 51% negative, 36% intermediate and 13% strong positive MLC responses. Identity for only one HLA-D antigen resulted in 3% negative, 40% intermediate and 57% strong MLC reactions. When no HLA-D antigen was shared, 88% of the reactions were strongly positive. HLA-D antigens behaved as equipotent stimulators in MLC between half-identical pairs. The only exception consisted of the higher frequency of weak responses displayed by the Dw5 positive individuals against stimulators differing by LD107. The same pattern was observed when LD107 homozygous cells were used as stimulators, suggesting that determinants of this specificity might be partially included in Dw5.