Ultrastructural analysis of HNK-1 + cells in human peripheral blood and lymph nodes

Abstract

HNK-1 positive (HNK-1+) cells in human peripheral blood and lymph nodes were comparatively analysed by means of immunohistochemistry and immunoelectron microscopy. In peripheral blood, the HNK-1' cells were grouped into large granular lymphocytes (LGLs), small lymphocytes and intermediate forms, al1 of which had many fine cytoplasmic processes. Except for smoothsurfaced lymphocytes, they could not be distinguished from helperlinducer T (OKT41Leu3a) cells and suppresssor/cytotoxic T (OKT81Leu2a) cells. In double staining, HNKlfT3- cells and HNK-1+T3+ cells could not be clearly distinguished in terms of morphology, although the former contained many LGLs. The HNK-1+ cells in the lymph nodes accumulated in the light zones of the germinal centers (GCs). These cells were small to medium-sized lymphocytes with few electron-dense granules and exclusively co-expressed helperlinducer T cell antigens (HNK-1+T4+). Their cytoplasmic projections were interwoven with those of the follicular dendritic cells which trap immune complexes for a long duration. These configurations suggesl that HNK-1+T4+ cells in GCs are engaged in an immunological regulation of germinal center cells. On the other hand. large blastic HNK-1+ cells were scattered outside the GCs and some of them were in the process of mitosis. Furthermore, HNKl+ LGL-like cells with a few large electron-dense granules were rarely seen. These observations indicate that the HNK-1+ cells in the lymph nodes may proliferate outside GCs and differentiate into LGLs with a strong natural killer function.