Regulation of macrophage activation markers by IL-4 and IFN-gamma is subpopulation-specific

Enhanced Dendritic Cell-Mediated Antigen-Specific CD4+ T Cell Responses: IFN-Gamma Aids TLR Stimulation

Phenotypic maturation and T cell stimulation are two functional attributes of DCs critical for immune induction. The combination of antigens, including those from cancer, with Toll-like receptor (TLR) ligands induces far superior cellular immune responses compared to antigen alone. In this study, IFN-gamma treatment of bone marrow-derived DC, followed by incubation with the TLR2, TLR4, or TLR9 agonists, enhanced DC activation compared to TLR ligation alone. Most notably, the upregulation of CD40 with LPS stimulation and CD86 with CpG stimulation was observed in in vitro cultures. Similarly, IFN-gamma coinjected with TLR ligands was able to promote DC activation in vivo, with DCs migrating from the site of immunization to the popliteal lymph nodes demonstrating increased expression of CD80 and CD86. The heightened DC activation translated to a drastic increase in T cell stimulatory capacity in both antigen independent and antigen dependent fashions. This is the first time that IFN-gamma has been shown to have a combined effect with TLR ligation to enhance DC activation and function. The results demonstrate the novel use of IFN-gamma together with TLR agonists to enhance antigen-specific T cell responses, for applications in the development of enhanced vaccines and drug targets against diseases including cancer.

Dependence of bacterial protein adhesins on toll-like receptors for proinflammatory cytokine induction

Toll-like receptors (TLRs) are important signal transducers that mediate inflammatory reactions induced by microbes through pattern recognition of virulence molecules such as lipopolysaccharide (LPS) and lipoproteins. We investigated whether proinflammatory cytokine responses induced by certain bacterial protein adhesins may also depend on TLRs. In differentiated THP-1 mononuclear cells stimulated by LPS-free recombinant fimbrillin (rFimA) from Porphyromonas gingivalis, cytokine release was abrogated by monoclonal antibodies (MAbs) to CD14 and TLR4 but not to TLR2. Similar experiments using anti-beta2 integrin MAbs suggested that beta2 integrins (CD11/CD18) also play a role in cytokine induction by rFimA or native fimbriae. Minor fimbriae (distinct from the fimA-encoded major fimbriae) of P. gingivalis induced proinflammatory cytokine release in a CD14- and TLR2-dependent mode. Cytokine induction by BspA, a leucine-rich repeat protein from Bacteroides forsythus, depended heavily on CD14 and TLR2. We also found that the ability of the streptococcal protein AgI/II to stimulate cytokine release depended partially on CD14 and TLR4, and the AgI/II segment that possibly interacts with these receptors was identified as its N-terminal saliva-binding region. When THP-1 cells were exposed to rFimA for 24 h, surface expression of CD14 and CD18 was decreased and the cells became hyporesponsive to cytokine induction by a second challenge with rFimA. However, tolerance induction was abolished when the THP-1 cells were pretreated with rFimA in the presence of either anti-CD14 MAb or anti-TLR4 MAb. Induction of cross-tolerance between rFimA and LPS correlated with downregulation of the pattern recognition receptors involved. Our data suggest that the CD14-TLR2/4 system is involved in cytokine production and tolerance induction upon interaction with certain proinflammatory bacterial protein adhesins.

Interleukin-4 and interferon-gamma: the quintessence of a mutual antagonistic relationship

The two cytokines interleukin (IL)-4 and interferon (IFN)-gamma play major roles in the generation and regulation of immune responses. Central in this respect is their mutually antagonistic functions. First, IL-4 promotes T helper cell type 2 (Th2) differentiation and stability and inhibits Th1-cell differentiation. A direct role of IFN-gamma in Th1-cell differentiation is debatable, whereas inhibition of Th2-cell differentiation and roles in Th1-cell stabilization are well established functions of IFN-gamma. Secondly, IL-4 and IFN-gamma also affect antibody class switch and expression of Fc receptors differentially, which strongly affect the effector mechanisms following antibody production. Thirdly, macrophage activities induced or enhanced by IFN-gamma, such as expression of certain cytokines, surface molecules and enzymes, are antagonized by IL-4. Together, these functions of IL-4 and IFN-gamma place the two cytokines at cardinal positions in the regulation of immune reactions. In this review the known molecular mechanisms underlying the observed functions of IL-4 and IFN-gamma are presented and discussed.

Identification and regulation of testicular interferon-gamma (IFNgamma) receptor subunits: IFNgamma enhances interferon regulatory factor-1 and interleukin-1beta converting enzyme expression

Interferon-gamma (IFNgamma) transmits its signal through a specific cell surface receptor (IFNgammaR), which consists of a primary ligand binding alpha-chain (IFNgammaR alpha) and a signaling beta-chain (IFNgammaR beta). Recent studies identified the cytokines IFNgamma, interleukin-6 (IL-6), IL-1alpha, and tumor necrosis factor-alpha in testicular cells. Therefore, we: 1) examined the expression of IFNgammaR alpha and IFNgammaR beta subunits in freshly isolated and purified rat testicular cells; 2) examined the differential regulation of receptor components by cytokines using primary cultures of Sertoli cells; 3) identified the cell signaling pathway components of testicular IFNgammaR; and 4) characterized the functional role of testicular IFNgamma using primary Sertoli cells. We demonstrated the messenger RNAs for both chains of IFNgammaR in rat testicular cells using Northern hybridization analysis. Western blot analysis and immunocytochemistry showed that both specific IFNgammaR protein subunits were present in cultured primary Leydig and Sertoli cells prepared from the testes of immature rats. The expression of both IFNgammaR component messenger RNAs in cultured Sertoli cells was increased by its specific ligand (IFNgamma), as well as IL-1alpha and tumor necrosis factor-alpha, in both a time- and dose-dependent manner. IFNgamma-activation of the Janus (JAK) tyrosine kinases, JAK1 and JAK2 proteins, indicate that IFNgammaR, expressed in the Sertoli cell, is functional. Moreover, IFNgamma modulates the expression of interferon regulatory factor (IRF)-1 and IL-1beta converting enzyme genes in Sertoli cells. Thus, our data are suggestive of a role(s) for IFN-gamma in the regulation of distinct gene expression and cell-specific sensitivity to apoptosis in the testis.

T-cell cytokines may control the balance of functionally distinct macrophage populations

As monocytes differentiate into mature macrophages, subsets emerge that exhibit stimulatory, suppressive or phagocytic potential. These functionally distinct subsets can be discriminated using monoclonal antibodies RFD1 and RFD7. As examples of all these subsets have been repeatedly identified within the macrophage pool in a variety of organs the overall functional capacity of this pool will depend on the relative balance of these subpopulations. This study investigates whether this balance present in mature macrophage populations can be regulated by the local influence of T-cell-derived cytokines. The dose-dependent effect of cytokines interferon-gamma (IFN-gamma), interleukins (IL) IL-2, IL-4 and IL-10 on the phenotype and function of monocyte-derived macrophages was determined. Subsets of mature cells were quantified by identifying RFD1- RFD7- stimulatory cells (D1+); RFD1- RFD7+ phagocytes (D7+) and RFD1+ RFD7+ suppressive cells (D1 D7+). IFN-gamma and IL-4 increased the relative proportions of D1+ stimulatory cells and upregulated HLA-DR expression. IFN-gamma also increased the capacity of the mature macrophage pool to stimulate T-cell proliferation. IL-10 reduced the proportions of D1+ stimulatory cells while promoting the differentiation of D7+ phagocytes and D1/D7+ suppressive cells. IL-10 induced changes also reduced the functional capacity of the mature populations to stimulate T cells in auto and allogenic mixed lymphocyte reactions (MLR). IL-2 had no effect on differentiation of monocytes. Thus IL-4 and IFN-gamma are seen to induce the development of stimulatory macrophages while IL-10 promotes differentiation of monocytes to mature phagocytes and suppressive macrophages. It is concluded that mature macrophage phenotype is 'plastic' and under the control of T-cell-derived mediators. Furthermore, within the differentiating monocytes, phenotypic change appears to carry with it functional change, thus retaining the relationship between antigen expression and activity in the mature macrophage populations.

Stimulatory and inhibitory effects of interleukin (IL)-4 and IL-13 on the production of cytokines by human peripheral blood mononuclear cells: priming for IL-12 and tumor necrosis factor alpha production

The production of cytokines in monocytes/macrophages is regulated by several different cytokines that have activating or inhibitory effects. Interleukin (IL)-10, IL-4, IL-13, and transforming growth factor (TGF)-beta are usually considered to be the most important macrophage-deactivating factors, with inhibitory effects on cytokine production. Unlike IL-10 and TGF-beta, which appear to act as downmodulators of many phagocytic cell functions, the mode of action of IL-4 and IL-13 is more complex. Addition of IL-4 and IL-13 to peripheral blood mononuclear cell (PBMC) cultures inhibited production of IL-12, tumor necrosis factor (TNF)-alpha, IL-10, and IL-1 beta induced by lipopolysaccharide (LPS) or Staphylococcus aureus added simultaneously with the cytokines. However, pretreatment of PBMC with IL-4 or IL-13 for > or = 20 h enhanced the production of IL-12 and TNF-alpha in response to LPS or S. aureus several fold in these cells; this IL-4-induced priming for the two cytokines was inhibited by anti-IL-4 neutralizing antibodies. IL-4 priming also enhanced the accumulation of IL-12 and TNF-alpha mRNA induced by LPS and S. aureus. The enhanced accumulation of transcripts for the IL-12 p35 and p40 chains by IL-4 priming was reflected in enhanced secretion of both the IL-12 free p40 chain and the p70 heterodimer. These results suggest an unexpected complexity in the regulatory role of IL-4 and IL-13 in immune responses.

Immunophenotyping of murine peritoneal macrophages and lymphocytes by flow cytometry

Peritoneal cells include mainly macrophages and both T and B lymphocytes. We describe a simple procedure to analyze by flow cytometry the antigens expressed on macrophage and/or lymphocyte membranes. F4/80 and CR3 macrophage antigens were detected with anti-F4/80 and anti-Mac-1 monoclonal antibodies (mAb) respectively, CD4 and THY1.2 T lymphocyte antigens with GK1.5 and J1j mAbs respectively, B CD5 lymphocytes were identified with LY1.2 mAb and Fc gamma RII/Fc gamma RIII were detected with 2.4G2 mAb.

Modulation of macrophage function by transforming growth factor beta, interleukin-4, and interleukin-10

The findings reviewed above leave no doubt as to the complexity of actions of TGF-beta, IL-4, and IL-10 on monocytes/macrophages. Along with MDF, whose actions were recently reviewed elsewhere, TGF-beta, IL-4, and IL-10 are the only presently known, purified cytokines that have been shown to have strong macrophage-deactivating effects. However, none of them can be categorized as purely macrophage deactivating since they also exert macrophage-activating effects. In vitro, their effects, both in terms of extent and direction (activating vs. deactivating), are strongly influenced by the stimulation conditions (e.g., triggering signal, cytokine concentration, timing of cytokine addition), the species (mouse vs. human), the source (blood vs. peritoneal, alveolar, colostral) and the state of differentiation/activation of the macrophage (e.g., resting vs. inflammatory). In addition, TGF-beta, as well as IL-4 and IL-10, up- and/or downregulates the function of several cell types other than macrophages, which further hampers our ability to predict, on the basis of in vitro experiments with macrophages, possible effects during an immune response in vivo. Despite this complexity, the highly reductive approach of in vitro studies has revealed important differences in the ability of TGF-beta, IL-4, and IL-10 to modulate the phenotype of monocytes/macrophages. The disparities have been most striking with regard to the secretory function of monocytes/macrophages (see Table 2). First, TGF-beta, IL-4, and IL-10 have a different spectrum of activity. Thus, TGF-beta, but not IL-4 or IL-10, can induce resting human monocytes to produce TNF, IL-1, and IL-6. Second, they affect monokine and RNI and ROI production to a different extent. For example, IL-10 is an approximately 25-fold more potent suppressor of LPS-induced TNF production by mouse macrophages than is TGF-beta. Third, they differ in their ability to overcome additional activating stimuli, so that in the presence of LPS, IL-4, but not TGF-beta or IL-10 suppresses IFN gamma-induced RNI release. Fourth, their macrophage-deactivating effects require different stimulation conditions. Thus, IL-4, but not TGF-beta, interferes with RNI release strongly only after preincubation of the macrophages. Finally, these agents deactivate macrophages by distinct mechanisms. For example, IL-10 causes massive downregulation of TNF mRNA, whereas TGF-beta suppresses TNF release on a translational level. It will be a challenge to define clinical applications for these potent macrophage modulators on the basis of their different spectrum of activities. For TGF-beta and IL-4 such studies have already been initiated.

Effect of interferon-gamma on myelin basic protein-specific T cell line proliferation in response to antigen-pulsed accessory cells

We have shown previously that treatment of SJL/J mice with anti-interferon-gamma monoclonal antibody (mAb) exacerbated experimental allergic encephalomyelitis (EAE) only if administered at the time of encephalitogenic challenge. Here we investigate the role of interferon-gamma (IFN-gamma) and anti-IFN-gamma mAb in the early events of T cell activation in vitro. Pretreatment of murine peritoneal exudate cells (PEC) with IFN-gamma led to a significant increase in their ability to activate myelin basic protein (MBP)-specific, short-term T cell lines. When exogenous IFN-gamma was added to cocultures of T cells and MBP-pulsed PEC, the antigen-specific T cell proliferation was considerably reduced. Anti-IFN-gamma mAb added to these cultures neutralized the inhibitory effect of the exogenous IFN-gamma on T cell proliferation but had no visible effect on class II MHC expression by the antigen-pulsed PEC present in the same cultures. A reduction in T cell proliferation was also observed when the T cells were treated with IFN-gamma prior to coculture with the MBP-pulsed PEC. These results demonstrate that, on one hand, IFN-gamma enhances the ability of PEC to induce antigen-specific T cell proliferation but, on the other hand, acts on the T cells themselves by inhibiting their proliferation in response to the antigen-pulsed PEC. This may explain why treatment with anti-IFN-gamma antibody in vivo induces EAE exacerbation.