Inter- and intrainstitutional evaluation of automated volumetric capillary cytometry for the quantitation of CD4- and CD8-positive T lymphocytes in the peripheral blood of persons infected with human immunodeficiency virus. Site Investigators and the NIAID New CD4 Technologies Focus Group

Natural killer (NK) cells are large granular lymphocytes capable of human leucocyte antigen (HLA) unrestricted killing of tumour cells. A putative NK cell tumour-recognition molecule (NK-TR) was previously isolated and cloned. The predicted primary structure of the NK-TR revealed that the amino terminus of the protein shared high homology with cyclophilin proteins. In this study, we used rabbit antibodies directed against synthetic peptides corresponding to amino acids 476-497 of the NK-TR protein, to examine the expression of the NK-TR antigen in freshly purified human lymphocytes. Cell-surface staining experiments using these peptide antibodies indicated the presence of the NK-TR protein on the surface of human CD3+ T-cell populations purified from peripheral blood. There were individual donor differences in the levels of cell-surface expression of this antigen ranging from 35 to 90% in T lymphocytes and, NK cells purified from different healthy volunteers. The immunoreactivity of our peptide antibodies in immunoprecipitation showed that the NK-TR-related protein expressed in purified T cells is similar to that expressed in NK cells in terms of its electrophoretic mobility. Cell-surface staining experiments using the peptide antibodies revealed 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 revealed abundant expression of NK-TR-specific mRNA species in purified T cells. Furthermore, another mRNA species smaller than 7 kb was detected in both NK and T-cell populations of lymphocytes freshly isolated from peripheral blood. Expression at the cell surface of a cyclophilin-homologous protein in purified human T lymphocytes may indicate another function for the reported NK-TR protein, that is, distinct from tumour-cell recognition and cytosis.