Classification of leukemic cells by Ia alloantigens and complement receptors. Surface probes for cell differentiation.

Of particular interest in the study of cell membrane markers of leukemic cells were cytotoxic and immunofluorescent results obtained in comparing Ia alloantigen and complement receptor (CR) expression on normal leukocytic and leukemic cell types. Using discontinuous Ficoll gradients, Ia alloantigens were found on varying numbers of leukemic myelo- and lymphoblasts, and on the early stages of normal melocytes. Ia alloantigens, however, were not detectable on mature polymorphonuclear cells. This establishes human Ia alloantigens as cell surface differentiation markers. The appearance of complement receptors was observed later than that of Ia alloantigens. CR1 (EAC1-4b) showed up later in the differentiation than CR2 (EAC1-3d). Thus, an immunological discrimination between AML blasts and CML blast crisis blasts appears to be possible: AML blasts are mostly Ia-positive but CR-negative, whilst CML blast crisis cells are only 20-30% Ia-positive and carry complement receptors in at least equal amounts. The AML blast cell would appear as the less-differentiated cell type when compared to the CML blast crisis cells. The picture, however, remains complex since in CML blast crisis at least three different types of blast cells can be identified: an Ia-positive and an Ia-negative myeloid blast as well as an Ia-positive lymphoid blast. The quantitative composition of these three elements within the myeloid differentiation profile can vary somewhat from patient to patient. Furthermore, these studies revealed a disturbed differentiation of leukemic cell types.