Novel p19 protein engages IL-12p40 to form a cytokine, IL-23, with biological activities similar as well as distinct from IL-12.

A novel sequence discovered in a computational screen appears distantly related to the p35 subunit of IL-12. This factor, which we term p19, shows no biological activity by itself; instead, it combines with the p40 subunit of IL-12 to form a novel, biologically active, composite cytokine, which we term IL-23. Activated dendritic cells secrete detectable levels of this complex. IL-23 binds to IL-12R beta 1 but fails to engage IL-12R beta 2; nonetheless, IL-23 activates Stat4 in PHA blast T cells. IL-23 induces strong proliferation of mouse memory (CD4(+)CD45Rb(low)) T cells, a unique activity of IL-23 as IL-12 has no effect on this cell population. Similar to IL-12, human IL-23 stimulates IFN-gamma production and proliferation in PHA blast T cells, as well as in CD45RO (memory) T cells.

Anti-interleukin 10 receptor monoclonal antibody is an adjuvant for T helper cell type 1 responses to soluble antigen only in the presence of lipopolysaccharide.

Soluble foreign antigen usually leads to a transient clonal expansion of antigen-specific T cells followed by the deletion and/or functional inactivation of the cells. As interleukin (IL)-10 is a key immunoregulatory cytokine, we questioned whether neutralization of IL-10 during priming with soluble antigen could prime for a subsequent T helper cell type 1 (Th1) effector recall response. By using an adoptive transfer model to track the fate of antigen-specific T cell receptor (TCR)-transgenic CD4(+) T cells, we show that administration of soluble ovalbumin (OVA) protein, but not OVA(323-339) peptide antigen, together with an anti-IL-10 receptor (R) mAb led to the enhancement of a Th1 response upon rechallenge. Lipopolysaccharide (LPS) present in the protein was necessary for priming for Th1 recall responses in the presence of anti-IL-10R mAb, as removal of LPS abrogated this effect. Moreover, addition of LPS to the peptide did not itself allow priming for recall Th1 effector responses unless endogenous levels of IL-10 were neutralized with an anti-IL-10R mAb. A significant increase in OVA-specific IgG1 and IgG2a isotypes was observed when the protein antigen was administered with anti-IL-10R mAb; however, this was not the case with peptide antigen administered together with anti-IL-10R and LPS. Our data, showing that LPS receptor signaling and neutralization of endogenous immunosuppressive cytokines is essential for Th1 priming, has important implications for the design of relevant vaccines for effective in vivo immunotherapy.

Molecular and functional characterization of mouse signaling lymphocytic activation molecule (SLAM): differential expression and responsiveness in Th1 and Th2 cells.

Optimal T cell activation and expansion require engagement of the TCR plus costimulatory signals delivered through accessory molecules. SLAM (signaling lymphocytic activation molecule), a 70-kDa costimulatory molecule belonging to the Ig superfamily, was defined as a human cell surface molecule that mediated CD28-independent proliferation of human T cells and IFN-gamma production by human Th1 and Th2 clones. In this study, we describe the cloning of mouse SLAM and the production of mAb against it which reveal its expression on primary mouse T and B cells. Mouse SLAM is expressed on highly polarized Th1 and Th2 populations, and is maintained on Th1, but not on Th2 clones. Anti-mouse SLAM mAb augmented IFN-gamma production by Th1 cells and Th1 clones stimulated through the TCR, but did not induce IFN-gamma production by Th2 cells, nor their production of IL-4 or their proliferation. Mouse SLAM is a 75-kDa glycoprotein that upon tyrosine phosphorylation associates with the src homology 2-domain-containing protein tyrosine phosphatase SHP-2, but not SHP-1. Mouse SLAM also associates with the recently described human SLAM-associated protein. These studies may provide new insights into the regulation of Th1 responses.

GATA-3 significantly downregulates IFN-gamma production from developing Th1 cells in addition to inducing IL-4 and IL-5 levels.

IL-12 and IL-4 are dominant factors driving the development of Th1 and Th2 cells, respectively, by their activation of Stat-4 and Stat-6 signaling molecules. Activation of Stat factors, although specific, is a rapid event; however, differentiation of Th cells takes place over several days. Thus, it is unlikely that the expression of effector cytokines is mediated solely by Stat factors. Recently there have been indications that link other molecular factors to Th subset development. The transcription factor GATA-3 is selectively expressed in Th2 cells and has been shown to induce the expression of Th2 cytokines in developing Th1 cells. Using retroviral infection of naive T cells to introduce GATA-3 cDNA, we measured its direct effects on the development of Th1 cytokine production. We now show that ectopic expression of GATA-3 in developing Th1 cells significantly inhibits IFN-gamma, as well as enhancing IL-4 and IL-5 production. Furthermore, GATA-3 inhibits production of IFN-gamma by developing Th1 cells in the complete absence of IL-4. Thus, antagonism of Th1 development by GATA-3 may facilitate rapid divergence of Th subsets toward a Th2 phenotype in concert with other factors.

IL-1 alpha and TNF-alpha are required for IL-12-induced development of Th1 cells producing high levels of IFN-gamma in BALB/c but not C57BL/6 mice.

The development of Th1- or Th2-type responses determines the type of immune response that is elicited in response to Ag. Responsiveness to IL-12 is critical for the development of Th1-type CD4+ T cells required for cell-mediated immune responses. Addition of IL-12 to primary cultures of CD4+ T cells stimulated with OVA and splenocytes or dendritic cells resulted in the development of a Th1 phenotype with the capacity to secrete high levels of IFN-gamma upon restimulation with splenic APC. The present study shows that using dendritic cells to present Ag upon restimulation reveals a requirement for additional cofactors, including IL-1 alpha and TNF-alpha, which were provided by spleen cells but not dendritic cells. Furthermore, these cofactors are required for optimal IL-12-induced Th1 development in BALB/c but not C57BL/6 mice. This differential requirement for such cofactors in IL-12-driven Th1 development may play a role in genetic predisposition to Th1 or Th2 responses to infectious agents.

IGIF does not drive Th1 development but synergizes with IL-12 for interferon-gamma production and activates IRAK and NFkappaB.

In these studies, IFN gamma-inducing factor (IGIF), unlike IL-12, did not drive Th1 development in BALB/c or C57BL/6 mice, but like IL-1alpha, potentiated IL-12-driven Th1 development in BALB/c mice. IGIF and IL-12 synergized for IFN gamma production from Th1 cells. Unlike IL-1alpha, IGIF had no effect on Th2 cells. IGIF signaled through IRAK, IL-1 receptor-associated kinase, to induce nuclear translocation of p65/p50 NFkappaB in Th1 cells. IL-1alpha had no effect on proliferation, cytokine production, or NFkappaB activation in Th1 cells but activated NFkappaB and proliferation in Th2 cells. Thus, Th1 and Th2 cells may differ in responsiveness and receptor expression for IL-1 family molecules. IGIF and IL-1alpha may differentially amplify Th1 and Th2 effector responses, respectively.