HNK-1 monoclonal antibody (Leu-7) in the identification of abnormal expansions of large granular lymphocytes.

Among 12 cases of chronic T lymphoproliferative disorders we observed, six patients showed an expansion of mononuclear cells with azurophilic granules usually referred to as large granular lymphocytes or LGL. Cells obtained from five patients with these abnormal LGL proliferations were studied with several surface markers including their reactivity with the HNK-1 monoclonal antibody reported to be specific for LGL. Cells in four out of five cases were HNK-1 positive. Whereas normal LGL have been reported to be unreactive with several T cell markers, three cases showed the co-existence of HNK-1 and surface markers expressed by T cells. Two cases were characterized by the proliferation of OKT8 cells. Cells from one patient were HNK-1 positive but did not express T or monocytic antigens. These cells were apparently not completely mature since alpha-naphthyl acetate acid esterase activity was negative. Cells from the remaining case were HNK-1 negative and positive for T and monocytic antigens. An increase of OKT-10 cells was observed in only one patient. Our data indicate that proliferations of LGL represent a remarkable proportion of the rare cases of sheep erythrocyte rosetting chronic lymphocytic leukaemias or lymphomas. Besides the morphology of LGL, the rosetting ability and the negativity for peroxidase, cells from these cases showed a vast heterogeneity of other structural and functional markers, possibly reflecting different stages in the maturation of these cells. The HNK-1 monoclonal antibody proved to be an important marker in the identification of these cases.