Interactions of murine leukemia virus (MuLV) with isolated lymphocytes. IV. The role of mitogen-induced cellular DNA synthesis in virus infection and replication

T-cells inhibit Friend murine leukemia virus infection of B-cells in vitro

The ability of splenic T-cells to regulate Friend murine leukemia virus replication in lipopolysaccharide-activated target B-cells infected in vitro was investigated. Removal of the T-cell fraction from spleen cells resulted in an 8- to 10-fold enhancement in the number of productively infected cells in the remaining B-cell-enriched fraction, as compared with unseparated spleen cells, and the addition of increasing numbers of purified T-cells to isolated B-cells prior to infection resulted in a directly proportional reduction in the number of B-cells releasing infectious progeny virus. Separation of splenic T-cells into Lyt 2- and Lyt 2+ T-cells before addition to infected B-cell cultures resulted in inhibition of infection only with the Lyt 2- T-cells; Lyt 2+ T-cells did not inhibit infection, even at high 1:1 ratios. Similarly, separation of splenic T-cells into L3T4+ and L3T4- T-cells before addition resulted in inhibition by L3T4+ but not L3T4- T-cells. Also, cytotoxic treatment of splenic T-cells with monoclonal anti-L3T4 antibody and complement before addition to B-cell cultures destroyed the regulatory effects. Finally, depletion of macrophages from both T-cells and B-cells before infection and coculture had no effect on the ability of T-cells to regulate B-cell infection. Collectively these results demonstrate that L3T4+ T-cells can inhibit Friend murine leukemia virus replication in target B-cells. Culture of isolated splenic T-cells with Friend murine leukemia virus in vitro resulted in the induction of alpha/beta but not interferon-gamma synthesis and in some experiments interferon-containing supernatants from T-cell-virus cultures were able to mediate suppression of B-cell infection with Friend helper virus; the addition of antibody specific for interferon-alpha/beta to cultures inhibited the ability of T-cells to regulate B-cell infection.

Target cell heterogeneity in murine leukemia virus infection. III. Identification of susceptible Lyt 1+ and resistant Lyt 2+ T-cell subsets following in vitro infection with Friend murine leukemia virus

The susceptibility of splenic T-cell subpopulations to productive infection with Friend murine leukemia virus was determined after in vitro infection and stimulation with Con A. Con A enhanced the number of productively infected cells in unseparated spleen cells as well as in T-cell-enriched spleen cell fractions. Splenic T cells were fractionated into Lyt 1+ and Lyt 2+ subpopulations using both positive and negative selection techniques; susceptible splenic T cells were recovered in the Lyt 1+ fraction and specific cytotoxic treatment with anti-Lyt 1 antibody and complement reduced the number of infectious center-producing cells by greater than 87%. In marked contrast, Lyt 2+ splenic T cells were resistant to productive infection by Friend murine leukemia virus in vitro.

Target cell heterogeneity in murine leukemia virus infection. II. Demonstration of Friend leukemia-virus-permissive and non-permissive subsets of splenic T cells

The permissiveness of normal splenic lymphocytes to Friend murine leukemia virus was determined by enumeration of cells producing infectious MuLV following infection with Friend virus in vitro. The infection was enhanced greatly in the presence of mitogens in the culture medium. The number of infected cells in cultures stimulated with bacterial lipopolysaccharide increased progressively between days 1 and 7 whereas in cultures with concavalin A, the number of infected cells reached a maximum on days 3-4 post infection and then declined to the level observed in unstimulated cultures. The con-A-enhanced infection was absent in cultures of splenocytes from nude mice but was present in cultures from nude mice implanted with thymus glands 6 weeks or more before use as donors of spleen cells. The cells permissive to MuLV upon con-A stimulation segregated in the nylon-wool-adherent fraction (together with B cells involved in the LPS-dependent infection) whereas the nylon-non-adherent fraction, containing approximately 90% T cells, was refractory to in vitro infection. The con-A-dependent infectious centers were inhibited by cytotoxic treatment with anti-Thy 1.2 antibody plus complement. These results indicate the existence of two subpopulations of splenic T cells, a major nylon-non-adherent and a minor, nylon-adherent subpopulation, which are, respectively, non-permissive and permissive to MuLV-Friend.