CELLULAR-DISTRIBUTION OF A NATURAL-KILLER-CELL TUMOR RECOGNITION-RELATED SURFACE-ANTIGEN IN PURIFIED HUMAN-LYMPHOCYTES

Natural killer (NK) cells are large granular lymphocytes capable of hu man leucocyte antigen (HLA) unrestricted killing of tumour cells. A pu tative NK cell tumour-recognition molecule (NK-TR) was previously isol ated and cloned. The predicted primary structure of the NK-TR revealed that the amino terminus of the protein shared high homology with cycl ophilin proteins. In this study, we used rabbit antibodies directed ag ainst synthetic peptides corresponding to amino acids 476-497 of the N K-TR protein, to examine the expression of the NK-TR antigen in freshl y purified human lymphocytes. Cell-surface staining experiments using these peptide antibodies indicated the presence of the NK-TR protein o n the surface of human CD3(+) T-cell populations purified from periphe ral blood. There were individual donor differences in the levels of ce ll-surface expression of this antigen ranging from 35 to 90% in T lymp hocytes and NK cells purified from different healthy volunteers. The i mmunoreactivity of our peptide antibodies in immunoprecipitation showe d that the NK-TR-related protein expressed in purified T cells is simi lar to that expressed in NK cells in terms of its electrophoretic mobi lity. Cell-surface staining experiments using the peptide antibodies r evealed that the NK-TR-related protein is more abundantly expressed on the surface of purified T cells compared with NK cells. Northern blot analysis of the mRNA species transcribed in human lymphocytes reveale d abundant expression of NK-TR-specific mRNA species in purified T cel ls. Furthermore, another mRNA species smaller than 7 kb was detected i n both NK and T-cell populations of lymphocytes freshly isolated from peripheral blood. Expression at the cell surface of a cyclophilin-homo logous protein in purified human T lymphocytes may indicate another fu nction for the reported NK-TR protein, that is, distinct from tumour-c ell recognition and cytosis.