T. Crepaldi

EQUINE T LYMPHOCYTES EXPRESS MHC CLASS II ANTIGENS

Six anti‐HLA class II mouse monoclonal antibodies (mAbs) were used in conjunction with a rat monoclonal antibody raised against horse lymphocytes to define class II major histocompatibility complex (MHC) molecules in the horse. By utilizing an ELISA assay and complement dependent lymphocytotoxicity assay, five out of the six anti‐HLA class II antibodies and the rat anti‐horse monoclonal antibody were found to react with a high percentage of peripheral blood lymphocytes. Flow cytometry demonstrated a variable antigen density on peripheral blood lymphocytes and clear evidence for expression by lymphocytes that carried no detectable surface immunoglobulin. None of the antibodies reacted with equine platelets. The mAbs immunoprecipitated an antigenic complex of M, 29,000‐33,000 from horse lymphocytes. It appears that the distribution of MHC class II antigens in the horse is different from that in man but is similar to that in the dog, since MHC class II antigens are expressed on resting peripheral blood lymphocytes which lack membrane‐bound immunoglobulins. Correlations between the distribution of MHC class II antigens on lymphocyte subpopulations and their role in immunological phenomena may contribute to our understanding of the functional properties of these molecules.

New HLA antigenic determinant shared by A2 and a subtype of Bw16 molecules detected by a monoclonal antibody

Abstract A cytotoxic mouse monoclonal antibody AB10.58 identifies a new, genetically determined HLA epitope common to HLA-A2 and a Bw16 subtype. Specificity has been defined by population and family studies and lysostrip experiments.

NEW HLA CLASS I‐LIKE ALLOANTIGENS EXPRESSED ON BLAST CELLS

New β2‐microglobulin (β2‐m)‐associated, HLA‐linked alloantigens, selectively expressed on phytohaemagglutinin (PHA)‐activated lymphocytes, were identified using human alloantisera. Reactivity of the antisera against activated cells correlated with HLA‐A2, A10 and A28 specificities. The new alloantigens were undetectable on peripheral blood mononuclear cells, B lymphocytes and platelets using either the lymphocytotoxicity or the absorption techniques, and appeared on lymphocytes upon PHA activation, with time‐dependent kinetics. They were found on some, but not all, acute leukaemias of B, T and myeloid origin, being absent from chronic B lymphocytic leukaemias. The presence of the new β2‐microglobulin‐associated allospecificities was not correlated with the quantity of classical class I antigens present, as analysed on different cell types by flow cytometry. Thus, these antigenic determinants appear to be different from the classical HLA class I antigens and could be the human counterpart of the murine Qa system or of the second H‐2K gene.

IEF analysis of HLA molecules immunoprecipitated by putative anti-class I-like alloantisera.

Two human alloantisera, previously described as possibly detecting new beta 2‐microglobulin associated proteins, selectively expressed on HLA‐A2 and HLA‐A1 phytohaemagglutinin (PHA)‐activated lymphocytes, immunoprecipitated only molecules with the same isoelectric point as HLA‐A1 and A2 products. This result suggests that the selected alloantisera do not react with the products of an HLA class I locus different from ABC but probably recognize a new epitope arising on HLA‐A molecules upon conformational changes consequent to cell activation.

Characterization of a Murine Monoclonal Antibody Specific for Early Lymphohemopoietic Cells

Abstract This paper summarizes the results of the preliminary characterization of A10, a monoclonal antibody which recognizes an epitope not restricted to cells of a definite lineage, whereas it seems to be specific for an early differentiation antigen, very similar to that recognized by the OK T10 reagent.