Search

The characteristics of a novel T lineage-specific activation antigen, termed TLiSA1, are described. The antigen was detected with a mouse monoclonal antibody, LeoA1, that was raised against activated human T cells generated in mixed lymphocyte culture (MLC). The antigen became strongly expressed on T cells 48-72 h after stimulation with phytohemagglutinin, and retained expression on MLC-activated T cells after 10 d of culture. The antigen was absent from a range of human T, B, myeloid, fibroblast, and tumour cell lines, but was present on the surface of the interleukin 2 (IL-2)-dependent gibbon cell line MLA-144. Analysis of the antigen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitates obtained from activated human T cells demonstrated a broad band in the region of 70 kD, whereas precipitates obtained from MLA-144 revealed a single narrow band of 95 kD. The molecule was expressed with a maximum density of 66,000 copies per cell on the surface of MLC-activated T cell blasts, as assessed by Scatchard analysis. TLiSA1 was distinguished from the IL-2 receptor bound by the anti-Tac monoclonal antibody by demonstrating that the antigens did not comodulate or coprecipitate, and by constructing an IL-2-independent human T X T hybrid that expressed the TLiSA1 but not the Tac antigen. MLC with B lymphoblasts was used to generate cytotoxic T lymphocytes (CTL) specific for the stimulating cell, and anomalous killer (AK) cells able to kill melanoma target cells. The presence of LeoA1 or F(ab')2 fragments of the antibody from the beginning of coculture did not affect proliferation in these cultures, but did inhibit the induction of both CTL and AK cells from their precursors. This inhibition of differentiation by LeoA1 was confirmed under conditions of limiting dilution, where it was shown that the antibody reduced the frequency of CTL produced, and greatly (fourfold) reduced the frequency of AK cells generated from their precursors. We discuss the possibility that human CTL may express a differentiation factor receptor that is distinct from the receptor for IL-2.

The activation of human peripheral blood mononuclear cells (PBM) in culture leads to the generation of nonspecific killer cells. These cells, termed activated lymphocyte killer (ALK) cells, can kill fresh tumor cells and tumor cell lines, in addition to the natural killer (NK) cell sensitive target K562. ALK cells have features in common with both T and NK cells, but their nature and origin are unknown. In the present study, it is shown that ALK cells are in fact heterogeneous and can be generated from both large granular lymphocytes with the same phenotype as NK cells and from T cells. Cell populations enriched for NK cells, when cultured with lymphokines, rapidly acquired a T cell phenotype, enhanced cytolytic activity against K562, and the ability to lyse NK-insensitive target cells such as a melanoma cell line LiBr; these ALK cells were described as NK-like cells. On the other hand, of the cloned cells derived from PBM stimulated with irradiated B lymphoblasts and grown in lymphokines, the major proportion of cytolytic T cells (CTC) able to kill the specific stimulator lymphoblasts were also found to kill LiBr but not K562 cells. These ALK cells, which were derived from the same precursors as CTC, were designated anomalous killer (AK) cells. Consistent with this, the presence of the pan T monoclonal antibody UCHT1 from the beginning of mixed cell cultures inhibited the generation of CTC and of the AK-type of ALK cell, which killed melanoma cells, but not the NK type, which killed K562 targets. By contrast, at the effector cell level, the antibodies UCHT1 and OKT8 only blocked specific killing by CTC but did not block the killing of LiBr or of K562 targets by ALK cells. However, at the effector cell level there was additional evidence for the heterogeneity of ALK cells. Thus, monoclonal antibody 9.1C3, which blocks killing by freshly isolated NK cells, also blocked the killing of K562 targets by NK-like cells, but did not block B lymphoblast killing by CTC or melanoma cell killing by AK cells. It is concluded that after mixed lymphocyte culture, the majority of ALK cells measured by the killing of melanoma target cells arise from the same precursors and are under the same influences as classical CTC (AK cells), whereas cells killing K562 targets are derived from NK cells (NK-like cells). Once generated, the AK cells have a different mechanism of killing from both classical CTC and from NK and NK-like cells.(ABSTRACT TRUNCATED AT 400 WORDS)

A monoclonal antibody, 9.1C3, was used to investigate the mechanism of natural killer (NK) cell-mediated lysis. In addition to blocking NK cell function, the antibody blocked antibody-dependent cellular cytotoxicity against the K562 target cell at the effector cell level. The stage at which 9.1C3 antibody inhibited cytolysis was established with a Ca++ pulse technique, whereby it was shown that the antibody inhibited killing at a discrete step after the Ca++-dependent programming for lysis. The 9.1C3 antigen appeared to be associated with the T200 glycoprotein complex. Thus the 66 and 77 Kd proteins detected by 9.1C3 were also precipitated with a monoclonal antibody to T200, and in sequential immunoprecipitations, 9.1C3 antibody removed these bands from immunoprecipitates with antibody to T200. Also, in co-modulation studies, it was found that antibody to T200 co-capped the 9.1C3 antigen but that capping with 9.1C3 antibody did not induce co-modulation of the T200 antigen. Expression of the 9.1C3 and T200 antigens on different cell types, however, was not identical, and the 9.1C3 antibody did not immunoprecipitate high m.w. proteins in the region of 200 Kd. Functionally, in NK cell killing studies, the antibody to T200 used alone did not block but was synergistic with the 9.1C3 antibody. The differential effect of the enzymes pronase and trypsin on the cell surface expression of the 9.1C3 and T200 antigens reflected the ability of these enzymes to inhibit NK cell killing. These data suggest that the 9.1C3 antigen participates in a late event in the cytolytic pathway.

Human thymocytes differed from peripheral blood T cells, in that they did not proliferate in response to mouse monoclonal antibodies specific for the T3 antigen complex (UCHT1 and OKT3), even in the presence of T-cell growth factor (IL-2) or with monocytes plus IL-2. The failure to respond was not the result of inhibition by cortical thymocytes, since OKT6-negative cells also did not respond when tested under conditions of limiting dilution. Of more importance, these antibodies rendered human thymocytes unresponsive to the lectin phytohaemagglutinin when added before, during, or immediately after addition of the lectin, an effect which was much more profound than the decrease in mitogenesis caused with blood mononuclear cells. These results illustrate a clear difference between medullary thymocytes and peripheral T cells in their ability to respond to signals transduced through the T3 antigen complex.