Generation of cytotoxic cells in absence of blastogenesis by mouse leukemic cells in mixed cultures

HIV-mediated immunodepression: in vitro inhibition of T-lymphocyte proliferative response by ultraviolet-inactivated virus

In order to assess whether the human retrovirus HIV, like other animal retroviruses, is endowed with intrinsic immunosuppressive activity, we studied the effects of noninfectious, uv-irradiated virus on in vitro lymphocyte function. uvHIV preparations inhibited T-cell proliferation to mitogens and alloantigens, as well as mitogen-driven IL-2 production. The inhibitory effect, which was not exerted by uv-irradiated HTLV-I, was apparently not due to a decrease in cell viability and was likely associated with thermoresistant viral component(s). The suppression proved to be selective for T-cell responses, while sparing other lymphocyte functions, such as the B-cell proliferative response to a selective B-cell mitogen. The inhibitory effect of uvHIV was not counteracted by a substantial reduction in the number of monocytes or by indomethacin. Moreover, IL-1 production by monocytes was not affected upon virus incubation. On the other hand, the proliferative response of both CD4+ and CD8+ T-cell clones was inhibited by uvHIV, suggesting that T cells represent the actual target for the inhibitory effect. Although a sizeable decrease in IL-2 production was observed following uvHIV incubation, exogenous IL-2 was not capable of reversing the virus-induced suppression of the proliferation. The possibility that the immunosuppressive activity of noninfectious HIV contributes to the T-cell defect in infected patients by mechanisms other than the cytopathic effect on CD4+ T lymphocytes is discussed.

Leukemia-cell rejection due to T-region encoded antigens

The role of H-2- and T-region products in determining allogeneic cell rejection was evaluated in H-2 congenic and recombinant mice by transplanting A1ATH and A6ATL leukemia cell lines induced in A.TH and A.TL strains, respectively, by Moloney murine leukemia virus.--In K- or D-region incompatible hosts transplant failure was observed, while in I + T-region incompatible hosts either rejection or prolonged survival was seen. In mice preimmunized with spleen cells from I- and/or T-region incompatible donors, leukemia cells were rejected by mice immune only to T-region products, and accepted by mice immune only to I-region products.--Cell-mediated cytotoxicity studies confirmed in vivo results. Secondary CTLs specifically directed against I-region products did not lyse the A1ATH and A6ATL cells, and secondary CTLs from A.TH and A.TL mice sensitized against A6ATL and A1ATH cells respectively exerted a lytic action specific for T-region products, while no activity was observed against I determinants.--The data suggest that tumor-transplant rejection may also be governed by histocompatibility antigens encoded in the T region.

Lack of T-cell mediated cytotoxicity in M-MSV system depending on H-2 haplotypes

The H-2 restriction phenomenon was evaluated with regard to the immune response to Moloney sarcoma virus (M-MSV)-induced tumours in the mouse. Using an in vitro 51Cr release assay the lytic activity of lymphocytes from M-MSV immune strains of mice, including several H-2 recombinant strains, was determined on leukaemic cell lines originally induced in mice of different strains by neonatal infection with Moloney leukaemia virus. In analogy with other experimental models, it was observed that a compatibility between effector and target cells at the K and/or D regions is generally necessary and sufficient to obtain the cytotoxic effect. However, for the H-2d and H-2b haplotypes, identity at the K or D region respectively was not sufficient for lysis to occur. Attempts to demonstrate that this lack of activity might be associated with the absence of H-2 linked Ir responder genes, were not successful.

Proliferative response of H-2 incompatible leukocytes to an Abelson virus-induced lymphoma cell line apparently not expressing Ia-antigens

The proliferative response of normal lymph node cells from different mouse strains to an Abelson virus-induced leukemic cell line (MLVA) in mixed leukocyte culture (MLC) has been investigated. MLVA leukemic cells do stimulate a specific response and the stimulating determinants are controlled, most likely, by genes in the K-end of the H--2 complex. However, using two different anti-Ia sera and different assay systems, we were unable to detect the expression of Ia-antigens on MLVA. In addition, an alloantiserum raised against MLVA, and absorbed with P815, a nonstimulating mastocytoma cell line, showed no residual activity against MLVA cells.