Murine splenic T lymphocytes display maximal cellular myc gene (c-myc) expression already 3 h after concanavalin A stimulation and subsequent down-regulation before the onset of DNA synthesis. Stimulation by leucoagglutinin in the presence or absence of interleukin 2 leads to only low initial levels of c-myc-specific RNA which, however, increase later on. A similar pattern of c-myc expression is shown by the Lyt-2+ T cell subpopulation stimulated with either concanavalin A or leucoagglutinin in the presence of interleukin 2. Although [3H]thymidine incorporation was identical, the leucoagglutinin-stimulated Lyt-2+ T cells were void of any demonstrable c-myc-specific RNA at 3 h post-stimulation. Thus, the kinetics of c-myc expression in mouse T lymphocytes are not at all uniform, but depend on the mitogen and the subpopulation. In contrast, levels of c-ras-Ha-specific RNA were always low at early times, always increased towards the onset of DNA synthesis and down-regulation was not observed.

All but one* of the following articles represent comprehensive reports on a workshop held between 7 and 9 May 1981 at the Institute of Virology and Immunobiology, University of Wfuzburg, Federal Repub

AKR mice were treated with heterologous anti-gp71 antibodies under various conditions in order to establish the optimal criteria for effective suppression of leukemia development. The strongest effect was observed when mice were treated at birth; and when this regimen was used, prior treatment of the mothers did not provide additional protection. If treatment was delayed until Day 3 (Schwarz et al., 1979), the beneficial effect of the serum diminished sharply, emphasizing the presence of a narrow window very early in the life of the AKR mouse when antibody must be present in order to have an effect on subsequent leukemia development. A number of parameters were examined in the experimental mice and as in our previous study (Schwarz et al., 1979), suppression of leukemia, which occurred in 68% of the animals, correlated with elimination of viremia and appearance of natural antiviral antibodies. Interestingly, our results suggest that antibody therapy is primarily effective against the thymic form of the disease. The availability of nonviremic, antibody-positive animals afforded us the opporounity to examine if these characteristics could be transmitted to the offspring. From selected mating crosses, we successfully derived both F1 and F2 generations of AKR mice which possessed high titers of antiviral antibodies and were nonviremic at 21–28 weeks of age. It appeared that a maternal effect may be responsible for this phenomenon. The implications of these findings are discussed in relation to the development of AKR leukemogenesis.

The non-antigen specific, late acting T helper cell replacing factor TRF can be purified to greater than 99.9% by a combination of molecular sieving and hydrophobic chromatography. Ion exchange chromatography on QAE columns provides an additional means of purification. In the presence of 4M urea, the biological activity of TRF focuses as a single peak, with a Pi of 5.2 ± 0.1. A goat antiserum raised against partially purified TRF specifically inhibits its biological activity and also inhibits the generation of plaque forming cells in normal mouse spleen cultures. Preliminary results obtained with hybridomas derived from peripheral blood lymphocytes of the immunized goat fused with mouse myeloma P3X63Ag8 are described.

Over the last couple of years, it has become increasingly evident that the development of an antibody secreting plasma cell from a resting B lymphocyte which reacts with its relevant T dependent antigen may be a multisept event (1). Thus the notion that the initial triggering of proliferation, brought about by antigen plus a postulated antigen specific and mitogenic T cell signal, is in itself sufficient to induce the whole series of events, is certainly an oversimplification. Our own studies using the model antigens sheep red blood cells (SRBC) (2, 3) and DNP-keyhole limpet hemocyanin (DNP — KLH) (4, 5) in the murine system have led us to propose the model shown in figure 1. According to this model, resting B cells would have to undergo at least three types of reactions before they can turn into antibody producing cells. 1. They would have to get into contact with their relevant antigen via the Ig receptor. 2. A proliferation signal would have to be received (some antigens such as heterologous blood cells are able to give this signal by themselves, others may need the intervention of T cells for receptor cross linkage) (1), 3. proliferating “intermediary” cells would not automatically turn into antibody producing cells, but be dependent on an antigen non-specific T cell product, the T cell replacing factor TRF, in order to commence antibody production and secretion. (6, 7)

Nonantigen-specific mediators, the lymphokines, are intimately involved in the amplification of many of the cell-mediated immune reactions. The stimulation of T-cells by concanavalin A (Con A) has proved to be particularly well suited for the induction of highly active preparations. A frequently used source of T-cell-replacing factor (TRF)-like molecules are T-cells activated to alloantigens in irradiated semiallogeneic recipients. T-cells required for TRF production carry the Ly 1 + 2- phenotype, which is now being recognized as that of the classical helper cell. The TRF-like molecules are produced within the first 24 hours after the stimulation of T-cells. The production of TRF is also inhibited by the addition of tosyl-L-lysyl chloroketone, an inhibitor of proteases, to the cultures of T-cells confronted with Con A. The chapter illustrates the inhibition of the primary anti-sheep red blood cell (SRBC) response by the addition of isolated Fc-fragments. T-cells may also require a distinct signal before they can become functional effector cells. This signal seems to be mediated by soluble factors produced by other T-lymphocytes. The differentiation of T- and B-cells to their final functional states may be brought about by similar biological mediator substances.

Spleen cells of dinitrophenyl keyhole limpet hemocyanin (DNPKLH) primed and boosted mice produced a nonantigen-specific helper factor upon in vitro challenge with DNPKLH. This helper factor displays all of the biological characteristics so far described for TRF produced by allogeneic or Concanavalin A stimulation of mouse spleen cells. It restores the primary anti-SRBC response in nude spleen cultures following the same kinetics of action as T-cell-replacing factor (TRF). Conversely, TRF restores the primary in vitro immune response of nude spleen cultures to DNPKLH. TRF also restores the secondary anti-hapten IgG response of T-cell-deprived spleen cell cultures derived from DNPKLH primed and boosted mice. Here the need for carrier specificity is fully overcome. The data therefore suggest that TRF, as a nonantigen- specific maturation signal, is involved in the primary and secondary immune responses to both particulate and soluble antigens.

ALL mouse strains investigated possess cellular DNA sequences which are homologous to the genomes of endogenous C-type particles1. Also, major envelope glycoproteins of the oncoviruses2, such as GP71, are found on the surface of normal cells and they display a considerable polymorphism. An antigen serologically indistinguishable from AKR murine leukaemia virus (MuLV) GP71 is present in normal bone marrow cells of all mouse strains investigated but not in normal spleen cells3. Allogeneic4 and mitogenic stimulation5,6 of spleen cells have been reported to result in C-type particle synthesis in some but not all mouse strains. We report here that both T and B lymphocytes of mice express a GP71-like antigen on their surfaces if antigenically stimulated.

Treatment of STU mice with antiserum to the major glycoprotein (gp71) of Friend leukemia virus (FLV) was therapeutically active against massive infection with Friend or Rauscher viruses, whereas similar treatment with antisera to p12 and p15, two other proteins of the virion which are involved in surface reactions, were not effective. A more thorough study showed that the active principle is contained in the IgG fraction of gp71 antiserum and that treatment with this can lead to complete recovery of the mouse from FLV infection. As a consequence of the treatment, the host produces type-specific antibodies which are detectable by neutralization, radioimmunoassay with FLV gp71, and cytotoxic tests on FLV-infected cells. No significant change was observed in the pattern of autogenous antibodies directed against an AKR-type gp71 already present in normal mice. Treatment with immune serum instead of immune IgG or treatment with immune IgG at a later stage of infection with FLV (after 7 days p.i.) did not result in complete recovery of the mice. Paralysis of the host immune system by serum proteins and Friend virus, respectively, seems to be responsible for these phenomena. Some indication was obtained that the viral-induced paralysis can be overcome by combined inoculation of heterologous immune IgG and normal isogenic spleen and bone marrow cells.

We have recently reported that in the in vitro system of Mishell and Dutton (1) in which normally the 19s response is strongly T-cell dependent (2) the T-cell function can be replaced by a soluble factor (3). This soluble factor was derived from supernates of allogeneic spleen cells incubated for 24 hrs. and was called T-cell replacing factor, TRF. Our published data showed that the formation of TRF was dependent on the presence of T-cells and we suggested that TRF was actually a T-cell product. To substantiate this idea we now used allogeneic cells from different sources, that is, spleens, lymph nodes and thymus. Since the thymocytes contain a very small number of mature cells (4) which might be expected to participate in TRF production, the product derived from allogeneic thymocytes was fivefold concentrated.

Guanidine does not inhibit the translation of viral RNA into virus specific proteins but it seems to prevent the generation of functional viral polymerase from precursor material. In the presence of guanidine, “inhibitory protein (s) ” responsible for the shut-off of cellular protein synthesis are still produced provided that the multiplicities of infection are high. The incoming (parental) viral RNA appears to be functional as messenger for only a limited number of translational cycles.

Evidence is presented that the genome of the infecting poliovirus must be intact in order to achieve inhibition of cellular protein synthesis. Viral particles with a single lethal hit by treatment with hydroxylamine no longer participate in the inhibitory action of the virus. De novo protein synthesis is required for the inhibition to occur. The synthesis of cellular m-RNA is not necessary.

If cells are exposed to a mixture of hydroxylamine inactivated and infectious viruses the total rate of viral RNA-replication is lower than if the cells are infected with the same number of infectious viruses alone. This inhibitory influence of inactivated viruses depends on the ratio of infectious: inactivated viruses in the inoculum. One lethal hit by hydroxylamine suffices to produce the effect. In fact, viruses with few lethal hits inhibit more strongly than those with many lethal hits in their genome. There is also no replication of viral RNA with lethal hits if the cells are infected simultaneously both with active and inactive virus.