Continuous engagement of a self-specific activation receptor induces NK cell tolerance.

Natural killer (NK) cell tolerance mechanisms are incompletely understood. One possibility is that they possess self-specific activation receptors that result in hyporesponsiveness unless modulated by self-major histocompatability complex (MHC)-specific inhibitory receptors. As putative self-specific activation receptors have not been well characterized, we studied a transgenic C57BL/6 mouse that ubiquitously expresses m157 (m157-Tg), which is the murine cytomegalovirus (MCMV)-encoded ligand for the Ly49H NK cell activation receptor. The transgenic mice were more susceptible to MCMV infection and were unable to reject m157-Tg bone marrow, suggesting defects in Ly49H(+) NK cells. There was a reversible hyporesponsiveness of Ly49H(+) NK cells that extended to Ly49H-independent stimuli. Continuous Ly49H-m157 interaction was necessary for the functional defects. Interestingly, functional defects occurred when mature wild-type NK cells were adoptively transferred to m157-Tg mice, suggesting that mature NK cells may acquire hyporesponsiveness. Importantly, NK cell tolerance caused by Ly49H-m157 interaction was similar in NK cells regardless of expression of Ly49C, an inhibitory receptor specific for a self-MHC allele in C57BL/6 mice. Thus, engagement of self-specific activation receptors in vivo induces an NK cell tolerance effect that is not affected by self-MHC-specific inhibitory receptors.

Differential expression of LFA-3, Fas and MHC Class I on Ad5- and Ad12-transformed human cells and their susceptibility to lymphokine-activated killer (LAK) cells.

Adenovirus (Ad) E1A is a potent oncogene and has been shown to deregulate the expression of a large number of cellular genes leading to cellular transformation. Here we have analysed the expression of several immunomodulatory molecules on the surface of a set of human cell lines transformed with either Ad12 or Ad5. Human cells transformed with Ad12 demonstrated reduced expression of cell surface LFA-3, Fas and MHC class I when compared to Ad5-transformed cells. Furthermore, Ad12-transformed human cell lines demonstrated greater susceptibility to lysis by lymphokine-activated killer (LAK) cells, compared to Ad5-transformed human cell lines. In contrast, previous studies with rodent cells showed that both Ad5- and Ad12-transformed rat cells were susceptible to LAK cells. Thus, transformation of human cells with Ad5 or Ad12 results in differences in the expression of immunomodulatory molecules on the cell surface and differential recognition of these virus-transformed cells by immune effector cells.

Lymphokine activated killer cells in murine coxsackievirus B3 myocarditis.

The purpose of the present study was to determine whether lymphokine activated killer (LAK) cells were involved in the development of coxsackievirus B3 (CB3) myocarditis in both the acute viremic (Experiment I) and the subacute aviremic (Experiment II) stages. To induce LAK cells, recombinant human interleukin-2 (IL-2) was administered to CB3-infected mice subcutaneously daily, starting on day 0 in Experiment I and on day 7 in Experiment II for 7 days, respectively. The treated groups were compared to infected controls. Splenic lymphocytes of IL-2 treated mice were further cultured in vitro in IL-2 containing medium for 7 days, and LAK cell activity, i.e., cytotoxic activity of the lymphocytes against EL-4 tumor cells and against cultured fetal myocytes, was assayed by 51Cr-release method. In Experiment I, histologic scores, myocardial virus titers, and LAK cell activity did not differ significantly between IL-2 treated and untreated groups. In contrast, in Experiment II, there were more cellular infiltration associated with severe necrosis and higher LAK cell activity against EL-4 cells and cultured myocytes in IL-2 treated than in untreated groups. The presence of LAK cells was demonstrated in the subacute stage of murine CB3 myocarditis. Thus, the behavior of LAK cell activity may vary with the course of myocarditis, and enhanced LAK cell activity may be involved in the development of the disease.

IL-2-dependent HTLV-I-infected T cells escape from non-specific, MHC-unrestricted cellular cytotoxicity.

The susceptibility of NK cell-mediated cytolysis was compared between 5 human HTLV-I-transformed T cell lines and 10 newly established IL-2-dependent HTLV-I-infected lines. None of the cell lines were killed after 4 hr incubation with normal PBMC. However, after 20 hr, 3 HTLV-I-transformed lines were significantly lysed. All the HTLV-I-infected lines, except 2, weakly inhibited the NK cell-mediated lysis of K562 targets. They showed a reduced ability to bind normal PBMC as compared with control NK-sensitive T cell lines. The IL-2-dependent lines remained unaffected by PBMC from HTLV-I-infected individuals, including the autologous donors. In contrast to the HTLV-I-transformed lines, they were weakly lysed or not lysed at all by LAK cells and only 5 were killed by ADCC with HTLV-I+ sera and normal PBMC. Taken together, the results show that IL-2-dependent HTLV-I-infected T cells strongly resist NK cell-mediated cytolysis at a post-binding level and suggest that such cells may escape in vivo from non-specific, MHC-unrestricted cellular cytotoxicity.