Reactivity of Anti‐HLA Sera against Mouse Lymphocytes

The reactivity of anti‐HLA hyper‐immune sera was tested by the microlymphocytotoxicity technique (LCT) against a panel of mouse lymphocytes. Three levels of reactivity were observed: negative (immune sera titre 1: 20 or less), weak (titre 1: 40 to 1: 80 with a percentage of dead cells less than 50%) or strong (titre 1:60 or more with 100% killing). Thirteen normal human sera were non‐reactive. Eleven out of 60 hyper‐immune sera were strongly reactive. Tests using congenic lines showed that the reactivity was controlled at the H‐2 complex. One serum (COD‐RON) was studied in detail. When tested against a panel of strains carrying 10 different H‐2 haplotypes, it reacted strongly against lymphocytes H‐2d, ja, k, p and r; and did not react, or at least only weakly, against lymphocytes H‐2b, f, q, s and v. Tests using mouse strains carrying the recombinant H‐2 haplotypes h4, i5, i, y2, g, g2 and t1, suggested that the observed reactivity was directed against structures controlled at the K end of the H‐2 complex (H‐2.47?). Absorption‐elution experiments with human and murine lymphocytes and platelets confirmed that the structures recognised by serum CODRON were determined at the major histocompatibility complex.