Alloantigenicity of peripheral blood mononuclear leukocytes with deficiency of class-II MHC molecule. Results of two separate experiments using BALB/c (H-2^d) and C57BR (H-2^k) mice as transfusion recipients are shown in panel A and B, respectively. Panel C shows the result from one experiment using CBA mice as recipients. Recipient mice were treated with weekly transfusion (↓) of 25,000 T-cell–depleted peripheral blood mononuclear leukocytes from BL6 donor mice with homozygous (○) or heterozygous (•) deficiency of MHC class-II molecules. The development of antibodies to donor leukocytes was determined by immunofluorescent flow cytometry. Spleen MNL from normal BL6 mice were used as targets. The average antibody activities (mean ± SD) in the serum samples collected 1 week after the last transfusion are shown at the right side of each panel. The fluorescent intensities of preimmune serum for BALB/c, C57 BR, and CBA mice were 24, 22, and 26, respectively. Four of 10 C57BR recipient mice treated with homozygous deficient MNL became immunized. The anti-H2^b antibody activities of the four immunized C57 BR mice (*) were significantly lower than those of control mice (P = .02) (panel B). Only one CBA mice became immunized (**).