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The anti-H-2 alloantiserum D-32 [(B10.A(2R) x C3H.SW) anti-C3H] is cytolytic to human lymphocytes. Fab2 blocking assays, indirect immunoprecipitation and sequential immunoprecipitation experiments showed that the anti-H-2 alloantiserum D-32 recognizes antigenic determinants which are expressed on the heavy chain of subpopulations of HLA-A, B antigens. These determinants are different from those defining the serological polymorphism of the HLA-A, B, C system, are the same as or spatially close to those recognized by the anti-HLA-A, B monoclonal antibody Q6/64 and are expressed on rabbit, rat or guinea pig lymphocytes.

Human T lymphocytes activated with PHA express Ia-like antigens and acquire the ability to stimulate autologous T lymphocytes in mixed lymphocyte reaction. This reaction is immunological in nature since it has specificity and memory. Ia-like antigens play a role in the stimulation of T lymphocytes by autologous PHA-T lymphocytes since monoclonal antibodies to Ia-like antigens can significantly, although not completely, inhibit the stimulation.

Murine monoclonal antibodies were generated against FG, a human pancreatic carcinoma (HPC) cell line. Of the six monoclonal antibodies, five (S3-15, S3-23, S3-41, S3-60, and S3-110) reacted by indirect immunoperoxidase assays with HPC of the ductal type, and another (S3-53) reacted with both ductal and acinar HPC. Strong reactivity was also found with tumors of the stomach, colon, mouth, lung, and cervix, while a large panel of normal human tissues displayed little reactivity. Indirect immunofluorescence staining revealed that, except for S3-23, the antigens recognized by these antibodies are expressed at the cell surface. Immunoprecipitation of metabolically radiolabeled FG cells indicated that the epitopes recognized by these antibodies are carried by distinct proteins or glycoproteins, differentiated on the basis of the apparent molecular weight and/or subunit composition as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This panel of antibodies will be useful to study antigenic variations associated with malignant cell transformation in HPC as well as other tumors.