Effect of acute nutritional deprivation on immune function in mice. I. Macrophages.

This study was designed to explore the effects of acute nutritional deprivation (starvation) on macrophage function in mice. In vivo macrophage activity was increased by starvation, as determined by multiplication of Listeria monocytogenes in both spleens and livers after intravenous injection. Similarly, in vitro studies revealed that the capacity of peritoneal macrophages to kill listeria was enhanced by starvation. This function was increased further by the addition of small concentrations of lipopolysaccharide (LPS; 10-100 ng/ml). The bactericidal activity of macrophages from starved mice, however, did not reach the levels observed with macrophages from BCG-infected mice. Furthermore, LPS did not appear to be an important second signal for macrophage activation in vivo, as LPS-unresponsive mice (C3H/HeJ and A/J) were protected by starvation. In contrast to these results we found that starved mice were not protected against Toxoplasma gondii infection and that macrophages from starved mice were unable to prevent multiplication of toxoplasma trophozoites in vitro. In toto, these experiments suggest that macrophage function is enhanced by starvation, but that this enhancement is not sufficient to fulfill all criteria for macrophage activation.     

Small CD4+8+TCRlow thymocytes contain precursors of mature T cells

To evaluate directly the developmental potential of cortical CD4⁺8⁺ thymocytes, highly purified populations of small, nondividing CD4⁺8⁺TCR^low and large, dividing CD4⁺8⁺TCR^high thymocytes from H-2^d mice expressing a transgenic T cell receptor restricted by H-2D^b (major histocompatibility complex class I) molecules were transferred into the thymus of normal, nonirradiated H-2^b recipient mice. The results show that both populations generate CD4^?8⁺ thymocytes under these conditions, thus providing conclusive evidence that small cortical thymocytes do not represent a “dead end” but an important intermediate stage in T cell development.     

Selective stimulation by B lymphocytes in the syngeneic mixed lymphocyte reaction

T and B lymphocytes from spleen and thoracic duct have been separated by preparative electrophoresis and their ability to stimulate syngeneic and allogeneic thymic cells in mixed lymphocyte cultures has been studied. In syngeneic mixed lymphocyte reaction (MLR), thymus cells from neonatal mice can only be stimulated by B lymphocytes from adult mice, whereas T and B lymphocytes are stimulatory for allogeneic thymus cells from neonatal and adult mice. The role of the syngeneic MLR as an example of self recognition and as a screening mechanism for depression of self-reactive cells is discussed.     

Cytotoxic T cell responses to haptenated cells III. Isolation and specificity analysis of continuously growing clones

Various procedures were used to derive continuously growing cytotoxic T lymphocyte (CTL) clones from a primary culture containing responder cells from immunized mice and 3-(p-sulfophenyldiazo)-4-hydroxylphenyl acetic acid (SP)-or fluorescein isothiocyanate (FL)-coupled stimulator cells. It seems likely that CTL have to undergo some change, possibly genetic, to be able to grow continuously in T cell growth factor conditioned medium in the absence of any stimulator or filler cells. The most convenient and reliable procedure to generate CTL clones with different specificities was to establish from several aliquots of a primary culture cell populations continuously growing in medium conditioned with T cell growth factor(s). Clones with different specificities segregated in the different populations. SP-and FL-specific CTL clones restricted to H-2K^k, and H-2D^d and two FL-specific CTL clones with no apparent H-2 restriction are described.     

Immunoglobulin turnover in B lymphocyte subpopulations

“In vitro” turnover of turnover of leucine-labeled and of radioiodinated IgM has been studied with cells from various lymphoid organs of nude mice, i.e. lymph nodes, thoracic duct, spleen and bone marrow, as well as with subpopulations of B cells fromspleen and bone marrow separated by free flow electrophoresis. Three types of IgM-producing lymphocytes could be distinguished by their turnover rates of IgM, by the size of the released IgM and by the capacity of the IgM molecules to be labeled by the lactoperoxidase-catalyzed radioiodination reaction and/or by incorporation of radioactive leucine. Type I cells release 7—8 S IgM rapidly (t_1/2 = 1—3 h); the released IgM is leucine-labeled and radioiodinated. Type II cells release 7—8S IgM slowly (t_1/2 = 10—30); the released IgM is leucine labeled and radioiodinated. Type III cells release 19 S IgM rapidly (t_1/2 = 2—4 h);the released IgM is leucine labeled, but not radioiodinated. Lymph nodesand thoracic duct contain predominantly type II cells, bone marrow contains type I and II cells, spleen contains type I, II and III cells. It is suggested that type III cells areIg-secreting, plaque-forming plasma cells, type II cells are small, resting “memory” B cells, and type I cells may be newly formed antigen-inexperienced B cells.     

Somatic activation of beta-catenin bypasses pre-TCR signaling and TCR selection in thymocyte development

Mutation or ablation of T cell factor 1 and lymphocyte enhancer factor 1 indicated involvement of the Wnt pathway in thymocyte development. The central effector of the Wnt pathway is beta-catenin, which undergoes stabilization upon binding of Wnt ligands to frizzled receptors. We report here that conditional stabilization of beta-catenin in immature thymocytes resulted in the generation of single positive T cells that lacked the alpha beta TCR and developed in the absence of pre-TCR signaling and TCR selection. Although active beta-catenin induced differentiation in the absence of TCRs, its action was associated with reduced proliferation and survival when compared to developmental changes induced by the pre-TCR or the alpha beta TCR.     

A human CD4 transgene rescues CD4−CD8+ cells in β2-microglobulin-deficient mice

The specificity of the αβ T cell receptor for class I or class II major histocompatibility complex (MHC) molecules determines whether a mature T cell will be of the CD4^?CD8⁺ or CD4⁺CD8^? phenotype, respectively. We show here that a human CD4 transgene can rescue a significant fraction of CD4^?CD8⁺ T cells in β2-microglobulin-deficient mice. Cells with this phenotype could be induced to become potent killers of targets expressing allogeneic MHC antigens, indicating that lineage commitment can precede the rescue of developing cells by the T cell receptor for antigen and the CD4 coreceptor.