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The present study concerns a panel of 33 acute non lymphoblastic leukaemia (ANLL) patients, previously typed for HLA-A,B serological specificities and including samples with a normal HLA-A,B phenotype (3,4 detected specificities) as well as samples with missing and extra specificities. Samples were analysed at the protein and/or RNA level in order to verify whether the observed typing anomalies were due to a modified quantitative expression of class I molecules. The number of HLA-A,B assigned specificities correlated significantly with the cell surface class I expression detected by indirect immunofluorescence using the monomorphic anti-class I MoAb W6/32 (Spearman rank correlation test, P < 0.01) and with the amount of class I Heavy Chain (HC, P < 0.05) and beta-2-microglobulin (beta 2m, P < 0.05) evaluated by Western blot in whole cell extracts. The RNA analysis suggested a HC-beta 2m coordinated down regulation at the mRNA level in a patient with no assigned HLA-A,B specificities. Another patient with no detectable HLA-A,B specificities showed a low expression selectively of the beta 2m protein. The results reported here demonstrate a heterogenous quantitative HLA class I expression in ANLL blasts, analogous to results reported for solid tumours.

HLA-A,B specificities were analysed on the neoplastic blasts of a panel of 69 lymphoblastic (ALL) and 50 non lymphoblastic (ANLL) acute leukaemias at onset using the standard lymphocytotoxicity technique. Analysis of the number of detected specificities per locus and, when possible, comparison of the results with those obtained on lymphocytes of the same patients during remission revealed many alterations in the expression of A,B specificities including extra specificities both at the HLA-A and -B loci mainly on lymphoblasts and missed specificities mainly at the HLA-B locus on myeloblasts. Lack of A,B antigens was complete in 6.2% of all tested samples (9% of ANLL) and selective for all the products of one locus in 16.8% of all tested samples (27.7% of ANLL). A decrease of class I molecules on the cell surface was evidenced with MoAb W6/32 on blasts missing detectable serological specificities.

New beta 2-microglobulin (beta 2-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 beta 2-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.