A heritable defect in IL-12 signaling in B10.Q/J mice. II. Effect on acute resistance to Toxoplasma gondii and rescue by IL-18 treatment

This study documents a defect in IL-12-dependent IFN-gamma responses in a substrain (B10.Q-H2-(q)/SgJ) of B10.Q mice that manifests as an acute susceptibility to infection by the intracellular protozoan pathogen, Toxoplasma gondii. Despite robust systemic production of IL-12, infected B10.Q/J animals fail to mount an early IFN-gamma response after parasite inoculation. Genetic experiments revealed that the host resistance and IFN-gamma production defects are determined by a single autosomal recessive locus distinct from the Stat4 gene. Nonetheless, a delayed IL-12-mediated IFN-gamma response emerges in later stages of acute infection but is unable to prevent host mortality. IL-18 administration restores, in an IL-12-dependent manner, the early IFN-gamma response and host resistance of B10.Q/J animals. These in vivo studies indicate that the partially impaired IL-12 responsiveness in B10.Q/J mice can result in defective host resistance and demonstrate a therapeutic function for IL-18 in reversing a genetically based immunodeficiency in IL-12-dependent IFN-gamma production.

Cbl-b regulates the CD28 dependence of T-cell activation

Whereas co-stimulation of the T-cell antigen receptor (TCR) and CD28 triggers T-cell activation, stimulation of the TCR alone may result in an anergic state or T-cell deletion, both possible mechanisms of tolerance induction. Here we show that T cells that are deficient in the adaptor molecule Cbl-b (ref. 3) do not require CD28 engagement for interleukin-2 production, and that the Cbl-b-null mutation (Cbl-b(-/-)) fully restores T-cell-dependent antibody responses in CD28-/- mice. The main TCR signalling pathways, such as tyrosine kinases Zap-70 and Lck, Ras/mitogen-activated kinases, phospholipase Cgamma-1 and Ca2+ mobilization, were not affected in Cbl-b(-/-) T cells. In contrast, the activation of Vav, a guanine nucleotide exchange factor for Rac1/Rho/CDC42, was significantly enhanced. Our findings indicate that Cbl-b may influence the CD28 dependence of T-cell activation by selectively suppressing TCR-mediated Vav activation. Mice deficient in Cbl-b are highly susceptible to experimental autoimmune encephalomyelitis, suggesting that the dysregulation of signalling pathways modulated by Cbl-b may also contribute to human autoimmune diseases such as multiple sclerosis.

Expression of Ly-6, a marker for highly malignant murine tumor cells, is regulated by growth conditions and stress

Ly-6E.1 is highly expressed in murine tumor cells with a high malignancy phenotype and may serve as a marker for such a phenotype. In this study, we examined the effects of various growth conditions and stress on the expression levels of Ly-6E.1 by tumor cells. Previous preliminary results have shown that murine DA3 mammary tumor cells expressing high levels of Ly-6E.1 (Ly-6(hi)) are more highly tumorigenic than the same tumor cells expressing low levels of this membrane protein (Ly-6(lo)). In this study, we demonstrate that mice bearing Ly-6(hi) DA3 tumors have a significantly higher burden of spontaneous pulmonary metastasis than mice bearing Ly-6(lo) DA3 tumors. Furthermore, the survival time of the former mice was significantly shorter than that of the latter ones. We further show that certain other members of the Ly-6 gene family such as Ly-6C.1 and Ly-6G.1 are coregulated with Ly-6E.1. This was shown to occur with respect to both DA3 cells as well as A3 tumor cells which are of fibroblast origin. However, these 2 cells differ with respect to regulation of Sca-2 (TSA1, another member of the Ly-6 family) expression on these cells. Levels of Sca-2 on A3 cells appear to be coregulated with Ly-6E.1 (i.e., Ly-6(hi) A3 cells express high levels of Sca-2 and Ly-6(lo) A3 cells express low levels of Sca-2). These 2 Ly-6 proteins were, however, not coregulated on DA3 cells. Both Ly-6(hi) as well as Ly-6(lo) DA3 cells express equal levels of Sca-2. Levels of Thy-1, another glycosylphosphatidylinositol (GPI)-anchored protein expressed by A3 tumor cells, were equally expressed by both Ly-6(hi) and Ly-6(lo) A3 tumor cells. Levels of Ly-6 (but not those of CD44) on A3 tumor cells were upregulated on cells from dense cultures but were not influenced by the position of the cells in the cell cycle. Stress conditions such as serum starvation or heat shock upregulated the expression of Ly-6 by the 2 types of tumor cells but did not induce apoptosis in these cells. The kinetics of the stress-dependent upregulation of Ly-6 expression differed, however, between the epithelial and fibroblastic tumor cells.

Activation of murine T lymphocytes with monoclonal antibodies: detection on Lyt-2+ cells of an antigen not associated with the T cell receptor complex but involved in T cell activation

A new T cell molecule defined by the mAb 143-4-2 has been identified that is involved in T cell activation. The expression of the 143-4-2-defined epitope is linked to the previously characterized Ly-6 locus and restricted to bone marrow cells and to a subset of peripheral Lyt-2+ cells. In comparison to other anti-Ly-6.2 mAb, the 143-4-2 mAb appears to be directed at an allogeneic determinant of the Ly-6.2C molecule. The anti-Ly-6.2C antibody can promote the lysis of antigen-non-bearing target cells by alloreactive CTL clones, and in the presence of cofactors (PMA or IL 2) induces a subset of Lyt-2+ cells to proliferate, perhaps through an autocrine pathway. Although the antibody described has antigen-like effects as described for anti-TcR complex reagents, studies performed with a recently derived anti-murine T3 mAb suggest that the Ly-6.2C molecule is not associated on the cell surface with components of the TcR complex. Nevertheless, cell surface expression of the TcR complex is required for optimal triggering of T cells via the Ly-6.2C molecule. Because Ly-6.2C determinants are expressed in bone marrow and not in the thymus, the possibility is considered that expression of this molecule identifies a distinct subset of extrathymically derived T cells.

Activation of murine T lymphocytes with monoclonal antibodies: detection on Lyt-2+ cells of an antigen not associated with the T cell receptor complex but involved in T cell activation

A new T cell molecule defined by the mAb 143-4-2 has been identified that is involved in T cell activation. The expression of the 143-4-2-defined epitope is linked to the previously characterized Ly-6 locus and restricted to bone marrow cells and to a subset of peripheral Lyt-2+ cells. In comparison to other anti-Ly-6.2 mAb, the 143-4-2 mAb appears to be directed at an allogeneic determinant of the Ly-6.2C molecule. The anti-Ly-6.2C antibody can promote the lysis of antigen-non-bearing target cells by alloreactive CTL clones, and in the presence of cofactors (PMA or IL 2) induces a subset of Lyt-2+ cells to proliferate, perhaps through an autocrine pathway. Although the antibody described has antigen-like effects as described for anti-TcR complex reagents, studies performed with a recently derived anti-murine T3 mAb suggest that the Ly-6.2C molecule is not associated on the cell surface with components of the TcR complex. Nevertheless, cell surface expression of the TcR complex is required for optimal triggering of T cells via the Ly-6.2C molecule. Because Ly-6.2C determinants are expressed in bone marrow and not in the thymus, the possibility is considered that expression of this molecule identifies a distinct subset of extrathymically derived T cells.

Monoclonal antibodies identify three epitope clusters on the mouse p55 subunit of the interleukin 2 receptor: relationship to the interleukin 2-binding site

A new rat monoclonal antibody (5A2) directed against the mouse interleukin 2 receptor (IL2R) is described. This antibody binds specifically to IL2R+ cells, competes with both cold IL2 and 125I-labeled IL2 for the IL2-binding site and inhibits IL2-induced T cell proliferation. This reagent was compared to five previously characterized rat monoclonal antibodies directed against the p55 subunit of the mouse IL2R. The capacity of all the antibodies to inhibit IL2-induced T cell proliferation was assessed. The relationship of these eight antibodies to each other and to the IL2-binding site was studied by cross-inhibition assays, and by Scatchard analysis of the data. The results indicate that the six monoclonal antibodies recognize epitopes in three areas of the p55 subunit of the mouse IL2R. Antibodies against two of the clusters affect IL2 binding. One cluster defined by 3 antibodies is probably located in the area of the IL2-binding site as there is competitive inhibition between IL2 and antibodies against this cluster. A single antibody directed against an epitope outside this cluster appears to inhibit IL2 binding by inducing a conformational change in the p55 subunit of the IL 2R. Two other antibodies identify a third region which is not involved in the formation of the binding site.

Interleukin 2 induces antigen-reactive T cell lines to secrete BCGF-I

Antigen-activated T lymphocytes produce within 24 h of stimulation a factor that is indistinguishable biochemically and functionally from the B cell co-stimulating growth factor, BCGF-I, originally identified in induced EL4 supernatants: Supernatants from antigen-stimulated T cell lines are not directly mitogenic for resting B cells, but synergize in an H-2-unrestricted manner with anti-Ig activated B cells to produce polyclonal proliferation but not antibody-forming-cell development; biochemical studies reveal the B cell co-stimulating factor present in antigen-stimulated T cell line supernatants is identical by phenyl Sepharose chromatography and isoelectric focusing (IEF) to EL4 supernatant BCGF-I. We thus conclude that normal T cells produce BCGF-I in response to antigenic stimulation. Analysis of the mechanism of BCGF-I production by antigen-stimulated T cells showed that optimum amounts of BCGF-I were obtained as quickly as 24 h post-stimulation, and that the factor producing cells in the T cell line investigated bore the Lyt-1+2- phenotype. As few as 10(4) T cells produced sufficient BCGF-I to support the proliferation of 5 X 10(4) purified anti-Ig activated B cells. Finally, the activation of normal T cell lines to produce BCGF-I required either antigen presented in the context of syngeneic antigen-presenting cells (APC) or interleukin 2 (IL-2).

Autoimmune encephalomyelitis: simultaneous identification of T and B cells in the target organ

Monoclonal antibodies to guinea pig T cells and antibodies to guinea pig immunoglobulin G were used in immunofluorescence studies to identify T and B cells in central nervous system tissue from guinea pigs with acute autoimmune encephalomyelitis. T cells appeared before B cells and were distributed within the white matter parenchyma, while B cells remained in perivascular spaces.

Partial N-terminal amino acid sequences of guinea pig classic histocompatibility antigens

Partial N-terminal amino acid sequences were determined by microsequencing for three of the guinea pig GPLA-B classic histocompatibility antigens, which are presumably allelic products. The sequences of GPLA-B.1 derived from the noncongenic inbred strain 2 and strain 13 animals showed no differences a their N-termini, suggesting that these molecules are chemically as well as serologically identical. Two residues, isoleucine and leucine, were found at position 5 of the sequence of GPLA-B.1, suggesting that GPLA-S, the product of the second classic histocompatibility locus, was being cosequenced. GPLA-B.2 and GPLA-B.3 antigens showed distinct sequence differences from GPLA-B.1 and from each other. The sequences of GPLA-B.3 derived from a random-bred guinea pig and from the inbred DHCBA strain showed no differences and showed a possible species specific residue. All sequences showed significant homology with histocompatibility antigens of other species, suggesting a common evolutionary origin.

Partial N-terminal amino acid sequences of guinea pig classic histocompatibility antigens

Partial N-terminal amino acid sequences were determined by microsequencing for three of the guinea pig GPLA-B classic histocompatibility antigens, which are presumably allelic products. The sequences of GPLA-B.1 derived from the noncongenic inbred strain 2 and strain 13 animals showed no differences a their N-termini, suggesting that these molecules are chemically as well as serologically identical. Two residues, isoleucine and leucine, were found at position 5 of the sequence of GPLA-B.1, suggesting that GPLA-S, the product of the second classic histocompatibility locus, was being cosequenced. GPLA-B.2 and GPLA-B.3 antigens showed distinct sequence differences from GPLA-B.1 and from each other. The sequences of GPLA-B.3 derived from a random-bred guinea pig and from the inbred DHCBA strain showed no differences and showed a possible species specific residue. All sequences showed significant homology with histocompatibility antigens of other species, suggesting a common evolutionary origin.

Structure of Guinea Pig Ia Antigens

Guinea pig Ia molecules bearing the markers 3, 5 and 7 (strain 13) and 4, 5 (strain 2) were isolated from spleen and lymph node cells. In the molecules bearing the 7 and the 4, 5 markers, the 25,000 and 33,000 MW polypeptide chains are linked by disulfide bonds. The molecules bearing the 3, 5 markers do not have polypeptide chains linked by disulfide bonds. These glycoproteins were metabolically labeled with tritiated amino acids and purified by NP-40 lysis, affinity chromatography on columns of lentil lectin and specific immunoabsorbents, followed by SDS-PAGE. In some cases the immunoabsorbent chromatography was replaced by immunoprecipitation using SaCI. The radioactive polypeptide chains were eluted from the gel and characterized by peptide mapping and by sequence analysis of the N-terminal regions of the 25,000 MW chains. The preliminary results indicate that all three 25,000 MW chains studied were homologous.

Linkage of C4 Deficiency to the Major Histocompatibility Locus in the Guinea Pig

C4 deficient (C4D) guinea pigs have a deficiency in C4 synthesis that appears to be due to a structural gene defect. Previous work has demonstrated that inheritance of this defect follows simple Mendelian laws. This report demonstrates linkage between C4D and an antigen controlled by a gene in the major histocompatibility complex of the guinea pig. Recent studies have defined a major histocompatibility locus (MHL) in the guinea pig (B) which appears to be equivalent to the D or K loci in the mouse, as well as a second region which resembles the mouse Ia. Four alleles of the B locus have been identified: B.1, B.2, B.3, B.4. Preliminary screening of the NIH multipurpose colony (the colony in which C4D was first observed) showed that 5 to 10% of the animals were homozygous for the B.1 antigen; the remaining animals had detectable B.3 antigen by serologic testing.

Requirement for T cells in the production of migration inhibitory factor

The question whether B lymphocytes are capable of being activated by antigen in the absence of functional T cells was investigated in a model that excludes participation of T cells by virtue of an immune response gene restriction. Strain 2 guinea pigs are capable of responding to immunization with DNP-PLL, whereas strain 13 animals are not. In the present experiments, animals of both strains were immunized with DNP-PLL complexed to ovalbumin (DNP-PLL-Ova) under conditions in which equal titers of antibodies to DNP were produced by both strains. The failure of T cells of strain 13 animals to respond to DNP-PLL was confirmed by the virus plaque assay. While spleen cells from both strains produced MIF after stimulation with DNP-PLL-Ova, in response to DNP-PLL only strain 2 spleens were able to produce MIF. Cells from neither strain could be activated by DNP-guinea pig albumin to produce MIF. We conclude that B lymphocytes are incapable of being stimulated by antigen in the absence of T cells, and that MIF production is a thymus-dependent response. While the results indicate that MIF production is a valid qualitative assay for T-cell competence, since MIF can be produced by B and T cells, the degree of migration inhibition cannot be regarded as a quantitative measure of T-cell function.

Production of migration inhibitory factor and lymphotoxin by non-T cells

Treatment of tuberculin-sensitive guinea pig spleen or lymph node cells with a burro anti-T cell serum plus complement diminished markedly the number of functionally detectable T cells, but did not affect the amount of migration inhibitory factor (MIF) or lymphotoxin produced by the residual T cell-depleted populations.

Alloantiserum-induced inhibition of migration inhibition factor production in immune response gene-controlled immune systems

We have previously demonstrated that alloantisera prepared by reciprocal immunization of strain 2 and strain 13 guinea pigs specifically block stimulation of in vitro DNA synthesis in genetically controlled systems. In order to determine whether this blockade extends to other T-lymphocyte functions, we examined the effect of alloantisera on the production of migration inhibition factor (MIF). (2 x 13)F(1) guinea pigs were immunized with a DNP derivative of the copolymer of L-glutamic acid and L-lysine (DNP-GL) and with DNP guinea pig albumin (GPA). The response to the former is controlled by a 2-linked Ir gene while that to the latter is mainly controlled by a 13-linked Ir gene. MIF production was assayed by an indirect procedure in which the migrating cell population lacked the histocompatibility antigen against which the alloantiserum was directed. Our results showed that anti-2 serum blocked MIF production by F(1) cells in response to DNP-GL but not DNP-GPA while anti-13 serum had the opposite effect. These experiments show that expression of a second major T-cell function is specifically blocked by alloantisera and suggest that Ir-gene products may act as antigen recognition substances on more than one type of T cell.

A human leukemia cell with both B and T cell surface receptors

Bone-marrow-derived (B) and thymus-derived (T) lymphocytes can be distinguished by the presence of a number of receptors and differentiation antigens. The presence of these markers has facilitated the identification and characterization of the mononuclear cells in a number of animal and human lymphoid malignancies. We describe here the immunological properties of human leukemia cells that are highly unusual, since they simultaneously bear the receptor for sheep erythrocytes characteristic of human T lymphocytes and the receptor for antigen-antibody-complement complexes characteristic of human B lymphocytes. A small number (about 2%) of normal human lymphocytes bearing both of these receptors was also identified.

The uropod-bearing lymphocyte of the guinea pig. Evidence for thymic origin

In this study, the frequency of uropod formation and the type of lymphocyte bearing the uropod was investigated in various guinea pig lymphocyte populations. Without prior in vitro stimulation, almost 40% of peritoneal exudate lymphocytes (PELS) form uropods, while thymocytes and lymph node cells form far fewer. Subsequent stimulation in vitro with purified protein derivative demonstrated that there is an association between antigen reactivity and frequency of uropod formation in these populations. The ultrastructure of these uropods is identical to that described for human lymphocytes stimulated with phytohemagglutinin. In the populations studied, all the lymphocytes forming uropods lack easily detectable surface membrane immunoglobulin and are therefore most likely thymus-derived or T lymphocytes.

Receptors for Immunoglobulin and Complement on Mouse Leukemias and Lymphomas

Bone marrow-derived B lymphocytes bear a receptor for antigen-antibody-complement complexes (EAC). Monocytes and macrophages also bear a receptor for EAC, but require the Mg++ ion for the attachment of EAC. A receptor for red cell IgG complexes (EA) is found on monocytes, but not on lymphocytes. Twenty-one mouse leukemias and lymphomas were examined for the presence of these receptors. None of the tumors studied bore the lymphocyte EAC receptor. One tumor bore both the monocyte EAC and EA receptors; two of the tumors bore the monocyte EA receptor alone. The binding of the IgG EA complex to both these tumor cells and to normal monocytes could be inhibited only by mouse myeloma proteins of the γF (γ1) and γH (γ2b) subclasses of mouse IgG.