Cytokines acting on or secreted by macrophages during intracellular infection (IL-10, IL-12, IFN-gamma)

Human dendritic cells require multiple activation signals for the efficient generation of tumor antigen-specific T lymphocytes

Dendritic cells (DC) are specialized cells of the immune system responsible for the initiation and regulation of both cellular and humoral responses. DC function is highly dependent on their level of maturation. In this study, we postulated that full DC maturation would require a combination of activating signals. When cultured monocyte-derived DC received stimulation with CD40 ligand (CD40L) and lipopolysaccharide (LPS) together, the IL-12 secretion increased 5-60-fold and the IL-10 secretion increased 5-15-fold when compared with either stimulation alone. In addition, poly I.C, a double-stranded RNA analog that mimics viral infection, also synergized with CD40L to stimulate DC to secrete high levels of IL-12 and IL-10. Flow cytometry revealed an up-regulation in the expression of CD80, CD86 and CD83 following activation with a soluble trimeric form of CD40L (CD40Ls) or LPS. However, no further up-regulation was observed when both CD40Ls and LPS were used together compared with a single stimulatory signal, suggesting that there was no correlation between the expression of these markers and the level of IL-12/IL-10 secretion. Finally, specific cytotoxic T lymphocytes (CTL) were generated using DC pulsed with a modified HLA-A2-restricted peptide epitope derived from the melanoma antigen MART-1. DC activated with a combination of CD40Ls and LPS were more efficient in eliciting MART-specific reactivity compared to DC activated with CD40Ls or LPS alone. These results demonstrate that multiple maturational signals have a positive impact on the ability of DC to secrete IL-12 and IL-10 and more importantly, to generate antigen-specific T lymphocytes.

Interferon-beta treatment in multiple sclerosis patients decreases the number of circulating T cells producing interferon-gamma and interleukin-4

Systemic administration of interferon (IFN)-beta has been recently approved for the treatment of relapsing-remitting multiple sclerosis (RRMS). The immunological mechanism by which IFN-beta ameliorates MS is still partially unknown. We measured the number of blood circulating CD4(+), CD4(-), CD8(+), and CD8(-) T cells secreting IFN-gamma and IL-4 in 26 RRMS patients followed for up to 9 months of an alternate day s.c. treatment with 8x16 IU of IFN-beta1b. Compared to pre-treatment values, a significant (P<0.05) reduction of CD4(+), CD4(-), CD8(+) and CD8(-) cells producing IFN-gamma and of CD4(+) and CD4(-) cells producing IL-4 was observed in MS patients. The IFN-beta-associated effect was evident soon after the beginning of the treatment and persisted for the entire follow-up period. We did not observe any effect of IFN-beta treatment on the percentage of IL-4-producing CD8(+) and CD8(-) cells nor in that of natural killer (NK) cells producing IFN-gamma. Our results show that IFN-beta treatment in MS patients induces a profound and persistent down-regulation of the number of circulating T cells secreting IFN-gamma and IL-4 thus suggesting a broader rather than a specific immunomodulatory effect of IFN-beta in MS.

IFN-alpha and IL-12 induce IL-18 receptor gene expression in human NK and T cells

IL-18 is a proinflammatory cytokine that enhances innate and specific Th1 immune responses. During microbial infections, IL-18 is produced by activated macrophages. IL-18 exerts its effects in synergy with IFN-alpha or IL-12 to induce IFN-gamma. Here we show that in human NK and T cells IFN-alpha and IL-12 strongly up-regulate mRNA expression of the IL-18R components, accessory protein-like (AcPL) and IL-1R-related protein (IL-1Rrp). In addition, IFN-alpha enhanced the expression of MyD88, an adaptor molecule involved in IL-18 signaling. Pretreatment of T cells with IFN-alpha or IL-12 enhanced IL-18-induced NF-kappaB activation and sensitized the cells to respond to lower concentrations of IL-18. AcPL and IL-1Rrp genes were strongly expressed in T cells polarized with IL-12, whereas in IL-4-polarized cells these genes were expressed at very low levels, indicating that AcPL and IL-1Rrp genes are preferentially expressed in Th1 cells. In conclusion, the results suggest that IFN-alpha and IL-12 enhance innate as well as Th1 immune response by inducing IL-18R expression.

Coadministration of interleukin-18 and interleukin-12 induces a fatal inflammatory response in mice: critical role of natural killer cell interferon-γ production and STAT-mediated signal transduction

The administration of therapeutic doses of recombinant cytokines to patients with malignant disease can be complicated by systemic toxicities, which in their most severe form may present as a systemic inflammatory response. The combination of interleukin (IL)–18 and IL-12 has synergistic antitumor activity in vivo yet has been associated with significant toxicity. The effects of IL-18 plus IL-12 were examined in a murine model, and it was found that the daily, simultaneous administration of IL-18 and IL-12 resulted in systemic inflammation and 100% mortality within 4 to 8 days depending on the strain employed. Mice treated with IL-18 plus IL-12 exhibited unique pathologic findings as well as elevated serum levels of proinflammatory cytokines and acute-phase reactants. The actions of tumor necrosis factor–α did not contribute to the observed toxicity, nor did T or B cells. However, toxicity and death from treatment with IL-18 plus IL-12 could be completely abrogated by elimination of natural killer (NK) cells or macrophages. Subsequent studies in genetically altered mice revealed that NK-cell interferon–γ mediated the fatal toxicity via the signal transducer and activator of transcription pathway of signal transduction. These data may provide insights into methods of ameliorating cytokine-induced shock in humans.

Coadministration of interleukin-18 and interleukin-12 induces a fatal inflammatory response in mice: critical role of natural killer cell interferon-γ production and STAT-mediated signal transduction

The administration of therapeutic doses of recombinant cytokines to patients with malignant disease can be complicated by systemic toxicities, which in their most severe form may present as a systemic inflammatory response. The combination of interleukin (IL)–18 and IL-12 has synergistic antitumor activity in vivo yet has been associated with significant toxicity. The effects of IL-18 plus IL-12 were examined in a murine model, and it was found that the daily, simultaneous administration of IL-18 and IL-12 resulted in systemic inflammation and 100% mortality within 4 to 8 days depending on the strain employed. Mice treated with IL-18 plus IL-12 exhibited unique pathologic findings as well as elevated serum levels of proinflammatory cytokines and acute-phase reactants. The actions of tumor necrosis factor–α did not contribute to the observed toxicity, nor did T or B cells. However, toxicity and death from treatment with IL-18 plus IL-12 could be completely abrogated by elimination of natural killer (NK) cells or macrophages. Subsequent studies in genetically altered mice revealed that NK-cell interferon–γ mediated the fatal toxicity via the signal transducer and activator of transcription pathway of signal transduction. These data may provide insights into methods of ameliorating cytokine-induced shock in humans.

T-cell activation follows Th1 rather than Th2 pattern in haemodialysis patients

BACKGROUND

Patients on chronic intermittent haemodialysis (HD) show an impaired cellular and humoral immune response that clinically appears with frequent infectious complications and low vaccination responses. This immune defect strongly correlates with reduced in vitro proliferative responses of T cells. The defect is localized in antigen presenting cells, which show a decreased co-stimulatory activity. Furthermore, the impaired immune response correlates with an increased production of pro-inflammatory cytokines. In response to primary activation, CD4 positive T helper (Th) cells mainly differentiate into either Th1 or Th2 cells. Th1 cells support cell mediated immunity whereas Th2 cells enhance humoral immune responses. Since both types of responses mutually inhibit each other, the impaired humoral immune response seen in HD patients could either be due to a reduced number of Th2 cells or to a predominant Th1 response.

METHODS

We analysed the Th cell profile in HD patients using flow cytometry. Monocytic cytokine expression was analysed using both flow cytometry and enzyme linked immunoadsorbant assays.

RESULTS

Our data demonstrate that the cytokine differentiation profile in circulating T cells from HD patients is dysregulated and characterized by an increase in Th1 cells, but a normal amount of Th2 cells. Moreover, the skewed helper cell responses correlate with a higher percentage of monocytes capable of secreting the Th1 promoting cytokine interleukin 12 (IL-12).

CONCLUSIONS

Our findings contribute to a better understanding of the pathogenesis of impaired cellular immune functions in dialysis patients and, in particular, the decreased antibody production after vaccination. They provide a link between overproduction of pro-inflammatory cytokines (IL-12) and imbalanced T-cell activation.

Critical roles for interleukin-4 and interleukin-5 during respiratory syncytial virus infection in the development of airway hyperresponsiveness after airway sensitization

In mice, respiratory syncytial virus (RSV) infection can enhance the consequences of allergic airway sensitization, resulting in lung eosinophilia and the development of airway hyperresponsiveness (AHR) to inhaled methacholine (MCh). To delineate a role for interleukin-5 (IL-5), interleukin-4 (IL-4), and interferon gamma (IFN-gamma) in mediating the effects of RSV infection on subsequent allergic sensitization, we treated BALB/c mice with anti-IL-5 during acute RSV infection but not during subsequent exposure to ovalbumin (OVA). IL-5-deficient and IL-4-deficient mice were also treated with IL-5 either during acute RSV infection or during the sensitization period. Airway responsiveness to inhaled MCh was assessed and numbers of lung eosinophils were monitored. Anti-IL-5 treatment during RSV infection reduced AHR and lung eosinophilia after subsequent exposure to allergen. In IL-5-deficient or IL-4-deficient mice lung eosinophilia and AHR after RSV infection and allergen exposure were also markedly reduced. IL-5 administration during RSV infection restored the responses to allergen in both IL-5- and IL-4-deficient mice. However, IL-5 administration only during sensitization restored these responses in IL-4-deficient but not in IL-5-deficient animals. IFN-gamma-deficient mice developed AHR and some lung eosinophilia after allergen exposure alone and when RSV infection preceded allergen, these responses were enhanced. We conclude that both IL-5, particularly during acute infection, and IL-4 are critical in mediating the effects of RSV infection on allergic airway sensitization, resulting in the development of AHR and lung eosinophilia.

Antimicrobial actions of the NADPH phagocyte oxidase and inducible nitric oxide synthase in experimental salmonellosis. II. Effects on microbial proliferation and host survival in vivo

The roles of the NADPH phagocyte oxidase (phox) and inducible nitric oxide synthase (iNOS) in host resistance to virulent Salmonella typhimurium were investigated in gp91phox(-/)-, iNOS(-/)-, and congenic wild-type mice. Although both gp91phox(-/)- and iNOS(-/)- mice demonstrated increased susceptibility to infection with S. typhimurium compared with wild-type mice, the kinetics of bacterial replication were dramatically different in the gp91phox(-/)- and iNOS(-/)- mouse strains. Greater bacterial numbers were present in the spleens and livers of gp91phox(-/)- mice compared with C57BL/6 controls as early as day 1 of infection, and all of the gp91phox(-/)- mice succumbed to infection within 5 d. In contrast, an increased bacterial burden was detected within reticuloendothelial organs of iNOS(-/)- mice only beyond the first week of infection. Influx of inflammatory CD11b(+) cells, granuloma formation, and serum interferon gamma levels were unimpaired in iNOS(-/)- mice, but the iNOS-deficient granulomas were unable to limit bacterial replication. The NADPH phagocye oxidase and iNOS are both required for host resistance to wild-type Salmonella, but appear to operate principally at different stages of infection.

Innate resistance to experimental African trypanosomiasis: differences in cytokine (TNF-alpha, IL-6, IL-10 and IL-12) production by bone marrow-derived macrophages from resistant and susceptible mice

Resistance to African trypanosomiasis is under multigenic control. BALB/c mice are highly susceptible while C57Bl/6 mice are relatively resistant. Macrophages eliminate opsonized trypanosomes from the bloodstream and are involved in immunosuppression. We therefore investigated the production of a number of cytokines (IL-10, IL-6, TNF-alpha and IL-12) by bone marrow-derived macrophages (BMDM) from C57Bl/6 and BALB/c mice following challenge with either Trypanosoma congolense or Trypanosoma brucei. BMDM from C57Bl/6 mice, upon challenge with whole cell extracts (WCE) of T. congolense or T. brucei, produced significantly more TNF-alpha and IL-12 than those from BALB/c mice. The production of these cytokines was significantly enhanced by pretreatment of the cells with IFN-gamma. BMDM from BALB/c mice, however, produced significantly more IL-6 and IL-10 than those from C57Bl/6 mice. In contrast to LPS stimulation, simultaneous treatment of cells with WCE and IFN-gamma enhanced IL-10 synthesis by BMDM from BALB/c mice. These results indicate that cytokine genes are differentially regulated in macrophages from trypanosome-susceptible and -resistant mice and are consistent with our previous findings wherein retrovirus-immortalized macrophage cell lines from BALB/c and C57Bl/6 mice produce differential amounts of cytokines after phagocytosis of trypanosomes.

An IFN-gamma-inducible transcription factor, IFN consensus sequence binding protein (ICSBP), stimulates IL-12 p40 expression in macrophages

IL-12 is a cytokine that links innate and adaptive immunity. Its subunit p40 is induced in macrophages following IFN-gamma/LPS stimulation. Here we studied the role for IFN consensus sequence binding protein (ICSBP), an IFN-gamma/LPS-inducible transcription factor of the IFN regulatory factor (IRF) family in IL-12 p40 transcription. Macrophage-like cells established from ICSBP-/- mice did not induce IL-12 p40 transcripts, nor stimulated IL-12 p40 promoter activity after IFN-gamma/LPS stimulation, although induction of other inducible genes was normal in these cells. Transfection of ICSBP led to a marked induction of both human and mouse IL-12 p40 promoter activities in ICSBP+/+ and ICSBP-/- cells, even in the absence of IFN-gamma/LPS stimulation. Whereas IRF-1 alone was without effect, synergistic enhancement of promoter activity was observed following cotransfection of ICSBP and IRF-1. Deletion analysis of the human promoter indicated that the Ets site, known to be important for activation by IFN-gamma/LPS, also plays a role in the ICSBP activation of IL-12 p40. A DNA affinity binding assay revealed that endogenous ICSBP is recruited to the Ets site through protein-protein interaction. Last, transfection of ISCBP alone led to induction of the endogenous IL-12 p40 mRNA in the absence of IFN-gamma and LPS. Taken together, our results show that ICSBP induced by IFN-gamma/LPS, acts as a principal activator of IL-12p40 transcription in macrophages.

IFN-beta-1b inhibits IL-12 production in peripheral blood mononuclear cells in an IL-10-dependent mechanism: relevance to IFN-beta-1b therapeutic effects in multiple sclerosis

IL-12 is a proinflammatory cytokine secreted by dendritic cells in response to microbial Ags and mitogens. IL-12 is thought to contribute to the pathogenesis of autoimmune diseases such as multiple sclerosis (MS). This is based on studies in experimental allergic encephalomyelitis and the demonstration that PBMC IL-12 production correlates with disease progression in MS. IFN-beta-1b is an effective treatment for MS, which is thought to involve in part inhibition of proinflammatory cytokines. In this study we examined the effect of in vitro treatment with IFN-beta-1b, on mitogen-induced IL-12 production in human PBMC and myelin basic protein-specific T cell lines obtained from healthy donors and MS patients. We demonstrate that IFN-beta-1b significantly inhibits inducible IL-12 p40 up to 80% and biologically active IL-12 p70 up to 70% beginning at a dose of 10 IU/ml. This inhibition is IL-10 dependent, as it could be blocked by anti-IL-10 but not anti-IL-4 or control Abs. Thus, endogenously produced IL-10 is a required cofactor for the IFN-beta-1b inhibitory effect on IL-12 to occur. We conclude that IFN-beta-1b has a profound inhibitory effect on PBMC IL-12 production in vitro, and that this effect is IL-10 dependent. These findings are potentially relevant to the therapeutic mechanism of IFN-beta-1b in MS.

Alteration at a single amino acid residue in the T cell receptor alpha chain complementarity determining region 2 changes the differentiation of naive CD4 T cells in response to antigen from T helper cell type 1 (Th1) to Th2

To study whether changes in the structure of a T cell receptor (TCR) at a single peptide-contacting residue could affect T cell priming with antigenic peptide, we made transgenic mice with a point mutation in the TCR alpha chain of the D10.G4.1 (D10) TCR and bred them to D10 beta chain transgenic mice. The mutation consisted of a leucine to serine substitution at position 51 (L51S), which we had already established contacted the second amino acid of the peptide such that the response to the reference peptide was reduced by approximately 100-fold. A mutation in the reference peptide CA134-146 (CA-WT) from the arginine at peptide position 2 to glycine (R2G) restored full response to this altered TCR. When we examined in vitro priming of naive CD4 T cells, we observed that the response to doses of CA-WT that induced T helper cell type 1 (Th1) responses in naive CD4 T cells from mice transgenic for the D10 TCR gave only Th2 responses in naive CD4 T cells derived from the L51S. However, when we primed the same T cells with the R2G peptide, we observed Th1 priming in both D10 and L51S naive CD4 T cells. We conclude from these data that a mutation in the TCR at a key position that contacts major histocompatibility complex-bound peptide is associated with a shift in T cell differentiation from Th1 to Th2.

Gram-positive bacteria are potent inducers of monocytic interleukin-12 (IL-12) while gram-negative bacteria preferentially stimulate IL-10 production

Interleukin-10 (IL-10) and IL-12 are two cytokines secreted by monocytes/macrophages in response to bacterial products which have largely opposite effects on the immune system. IL-12 activates cytotoxicity and gamma interferon (IFN-gamma) secretion by T cells and NK cells, whereas IL-10 inhibits these functions. In the present study, the capacities of gram-positive and gram-negative bacteria to induce IL-10 and IL-12 were compared. Monocytes from blood donors were stimulated with UV-killed bacteria from each of seven gram-positive and seven gram-negative bacterial species representing both aerobic and anaerobic commensals and pathogens. Gram-positive bacteria induced much more IL-12 than did gram-negative bacteria (median, 3,500 versus 120 pg/ml at an optimal dose of 25 bacteria/cell; P < 0.001), whereas gram-negative bacteria preferentially stimulated secretion of IL-10 (650 versus 200 pg/ml; P < 0.001). Gram-positive species also induced stronger major histocompatibility complex class II-restricted IFN-gamma production in unfractionated blood mononuclear cells than did gram-negative species (12,000 versus 3,600 pg/ml; P < 0.001). The poor IL-12-inducing capacity of gram-negative bacteria was not remediated by addition of blocking anti-IL-10 antibodies to the cultures. No isolated bacterial component could be identified that mimicked the potent induction of IL-12 by whole gram-positive bacteria, whereas purified LPS induced IL-10. The results suggest that gram-positive bacteria induce a cytokine pattern that promotes Th1 effector functions.

Chronic colitis in IL-10-/- mice: insufficient counter regulation of a Th1 response

IL-10-deficient (IL-10-/-) mice, generated by a gene-targeted mutation, develop abnormal immune responses as a result of uncontrolled interactions between antigen presenting cells and lymphocytes. The studies reviewed herein have focused on the enterocolitis that spontaneously develops in IL-10-/- mice. Not unexpectedly, heightened production of proinflammatory mediators accompanied pathologic changes in the gastrointestinal tract of young mutants. In a series of studies, the proinflammatory mediators responsible for initiating the pathogenic response were distinguished from those that were elicited as a consequence of persistent inflammation. We have also investigated the possibility that different mediators are involved in the inductive versus the maintenance phase of disease. The findings of these mechanistic studies as they relate to our understanding of progressive inflammatory disease and the role of IL-10 in controlling the acute and chronic stages are discussed.

Activation of alloreactive T cells by allogeneic nonprofessional antigen-presenting cells and interleukin-12 from bystander autologous professional antigen-presenting cells

BACKGROUND

After solid organ transplantation most alloantigens are presented to the recipient's immune system by normal tissue cells, which can be considered to act as nonprofessional antigen-presenting cells (APC). It is well accepted that such nonprofessional APC fail to activate recipient resting T cells due to their inability to deliver costimulatory activity. In our study, we tested a hypothesis that such costimulatory activity may be provided by "bystander" recipient professional APC.

METHODS

We set up mixed lymphocyte cultures (MLC) of purified T cell responders and T cell stimulator cells, the latter as nonprofessional APC carrying allogeneic MHC class I and II, and tested if responder-type autologous APC could facilitate responder T cell proliferation. In this assay also the effects of anti-CD28 antibody and interleukin- (IL) 1beta, IL-6, or IL-12 mediated costimulation on responder T cell proliferation and IL-2 production were investigated.

RESULTS

Autologous APC, i.e., monocytes, were found to facilitate the proliferative response of resting T cells stimulated by allogeneic nonprofessional APC. IL-12 was identified as the most important costimulatory factor for induction of proliferation. IL-1beta enhanced IL-2 production and proliferation of allostimulated resting T cells but its presence was not essential. Although CD28 triggering alone was ineffective, this costimulatory pathway enhanced IL-2 production and proliferation when combined with IL-12 or IL-1beta.

CONCLUSIONS

We conclude that costimulatory activity for activation of resting human T cells by nonprofessional donor APC can be delivered through activity of bystander recipient-type autologous APC. This mechanism of allostimulation may contribute to the induction and perpetuation of alloreactivity "in vivo" in a time frame when intragraft professional donor-type APC have been replaced with professional recipient-type APC.

Roles of interleukin-12 and gamma interferon in murine Chlamydia pneumoniae infection

BALB/c and strain 129 mice infected intranasally with Chlamydia pneumoniae displayed a moderate-to-severe inflammation in the lungs and produced interleukin-12 (IL-12), gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and IL-10, with peak levels on days 1 to 3 postinfection (p.i.), returning to basal levels by day 16 p.i. Anti-IL-12 treatment resulted in less-severe pathological changes but higher bacterial titers on days 3 and 7 p.i. By day 16 p.i., the inflammatory responses of control antibody-treated mice subsided. The bacterial titers of both anti-IL-12- and control antibody-treated mice decreased within 3 weeks to marginally detectable levels. Anti-IL-12 treatment significantly reduced lung IFN-gamma production and in vitro spleen cell IFN-gamma production in response to either C. pneumoniae or concanavalin A. In gamma-irradiated infected mice, cytokine production was delayed, and this delay correlated with high bacterial titers in the lungs. Following C. pneumoniae infection, 129 mice lacking the IFN-gamma receptor alpha chain gene (G129 mice) produced similar IL-12 levels and exhibited similarly severe pathological changes but had higher bacterial titers than 129 mice. However, by day 45 p.i., bacterial titers became undetectable in both wild-type 129 and G129 mice. Thus, during C. pneumoniae lung infection, IL-12, more than IFN-gamma, plays a role in pulmonary-cell infiltration. IFN-gamma and IL-12, acting mostly through its induction of IFN-gamma and Th1 responses, play an important role in controlling acute C. pneumoniae infection in the lungs, but eventually all mice control the infection to undetectable levels by IL-12- and IFN-gamma-independent mechanisms.

Control of CD4 T cell fate by antigen re-stimulation with or without CTLA-4 engagement 24 h after priming

After two consecutive inoculations with Staphylococcus enterotoxin B (SEB) at 24 h intervals in vivo, CD4 T cells became anergic to the antigen challenge in vitro. Administration of anti-CTLA-4 mAb in conjunction with the second SEB inoculation 24 h after antigen priming interfered with anergy and CD4 T cells became T(h)2 cells. However, the anergy induction was not ablated when SEB and anti-CTLA-4 mAb were administered 48 or 72 h after antigen priming. Moreover, anti-CTLA-4 mAb without SEB did not interfere with anergy nor promoted the T(h)2 differentiation. T-antigen-presenting cell (APC) interaction in vitro in the presence of high doses of antigen and anti-CTLA-4 mAb induced a T(h)2-polarizing cytokine IL-6 and IL-10. IL-10 then down-modulated a T(h)1-polarizing cytokine IL-12. The results demonstrate that 24 h after the initial antigen stimulation, CD4 T cells enter the critical activation phase where antigen re-stimulation with or without CTLA-4 engagement alters the fate of the cell, anergy or differentiation respectively. Once anergy is interfered with, T(h)2-polarizing cytokines produced upon prolonged T-APC interaction favor the T(h)2 differentiation.

Interleukin-12 neutralization alters lung inflammation and leukocyte expression of CD80, CD86, and major histocompatibility complex class II in mice infected with Histoplasma capsulatum

Histoplasma capsulatum induces a cell-mediated immune response in lungs and lymphoid organs of mammals. Resolution of primary infection in mice depends on interleukin-12 (IL-12), since neutralization of this monokine increases susceptibility to infection. The present study was designed to determine if blockade of IL-12 disrupts the protective immune response by altering the influx of lineage-specific cells into infected lungs and the numbers of cells expressing CD80, CD86, CD119, and major histocompatibility complex class II (MHC II) molecules. In mice given anti-IL-12, there was a 2.5-fold decrease in total numbers of T cells on days 3 to 10 of infection and a 4-fold increase in Mac-1/Gr-1(+) cells on days 7 and 10 compared to infected controls. CD80(+) lung cells from anti-IL-12-treated mice were 2- to 3-fold greater than those from controls on days 7 and 10, whereas the total numbers of CD86(+) cells were 2- to 3-fold less and MHC II(+) cells were 1.5- to 2-fold less on days 3 and 5. Cells expressing CD119 were reduced 1.5-fold on day 5. Treatment with monoclonal antibodies (MAb) to CD80, CD86, or both reduced the fungal burden slightly compared to that in rat immunoglobulin G-treated controls, whereas after IL-12 neutralization, blocking of CD80 reduced the tissue burden by 2. 5-fold and this correlated with a decrease in IL-4. Regardless, mortality was not altered by treatment with MAb to CD80 or CD86. We conclude that (i) IL-12 neutralization alters the nature of the inflammatory response in lungs and the expression of CD80 and CD86 on lineage-specific cells, (ii) the immune response during infection with H. capsulatum is controlled via mechanisms independent of the CD80 and CD86 costimulatory pathways, and (iii) decreased expression of CD86 and MHC II may modulate generation of optimal protective immunity.

Secretion of IL-12 by murine macrophages activated by immunoglobulin receptor-mediated internalization of the surface coat of Trichinella spiralis larvae

Trichinella spiralis larvae incubated with a rabbit antiserum raised against the larval surface coat bound murine macrophages to the parasite surface. Cell binding was not observed without the antisurface coat serum, or with incubation of larvae in normal rabbit serum, or with antibodies to keyhole limpet haemocyanin which identify a cryptic T. spiralis larval antigen. Cell adherence to the larval surface was lost by treatment of the cells with the lysosomotropic drug primaquine, implicating a receptor-mediated mechanism. Cells adhering to the parasite surface internalized parasite surface coat material, which was subsequently concentrated into endosomes. Culture supernatants from these cells contained enhanced levels of IL-12. Thus, the initial Th1 response to T. spiralis infection may be explained by these data.

Cutting edge: IL-15 costimulates the generalized Shwartzman reaction and innate immune IFN-gamma production in vivo

Sequential administration of LPS to SCID mice results in the generalized Shwartzman reaction, manifesting as rapid mortality via cytokine-induced shock. Here we demonstrate that in vivo neutralization of IL-15 before LPS priming significantly reduced lethality in this reaction (p = 0.0172). We hypothesize that LPS priming induces IL-12 and IL-15 that costimulate NK cell-derived IFN-gamma. Such IFN-gamma may then in turn sensitize macrophages to elicit the Shwartzman reaction following a subsequent LPS challenge. Supporting this, IL-12 and IL-15 synergized to induce murine NK cell IFN-gamma production in vitro. LPS stimulation of SCID mouse splenocytes resulted in measurable IFN-gamma production, which was reduced when IL-15 was neutralized or IL-2/15Rbeta was blocked. Pretreatment with either anti-IL-2/15Rbeta or anti-IL-15 Abs reduced serum IFN-gamma protein following LPS administration to SCID mice. Collectively, these data provide the first in vivo evidence that IL-15 participates in LPS-induced innate immune IFN-gamma production and significantly contributes to the lethal Shwartzman reaction.

CD47 engagement inhibits cytokine production and maturation of human dendritic cells

Upon encounter with bacterial products, immature dendritic cells (iDCs) release proinflammatory cytokines and develop into highly stimulatory mature DCs. In the present study, we show that human monocyte-derived DCs functionally express the CD47 Ag, a thrombospondin receptor. Intact or F(ab')2 of CD47 mAb suppress bacteria-induced production of IL-12, TNF-alpha, GM-CSF, and IL-6 by iDCs. 4N1K, a peptide derived from the CD47-binding site of thrombospondin, also inhibits cytokine release. The inhibition of IL-12 and TNF-alpha is IL-10-independent inasmuch as IL-10 production is down-modulated by CD47 mAb and blocking IL-10 mAb fails to restore cytokine levels. CD47 ligation counteracts the phenotypic and functional maturation of iDCs in that it prevents the up-regulation of costimulatory molecules, the loss of endocytic activity, and the acquisition of an increased capacity to stimulate T cell proliferation and IFN-gamma production. Interestingly, regardless of CD47 mAb treatment during DC maturation, mature DC restimulated by soluble CD40 ligand and IFN-gamma, to mimic DC/T interaction, produce less IL-12 and more IL-18 than iDCs. Finally, CD47 ligation on iDCs does not impair their capacity to phagocytose apoptotic cells. We conclude that following exposure to microorganisms, CD47 ligation may limit the intensity and duration of the inflammatory response by preventing inflammatory cytokine production by iDCs and favoring their maintenance in an immature state.

Early induction of interleukin-12 by human monocytes exposed to Cryptococcus neoformans mannoproteins

Interleukin-12 (IL-12) production by human monocytes stimulated with mannoproteins (MPs) of Cryptococcus neoformans was investigated. The results reported show that secreted or cell-associated MPs induce an early and significant production of IL-12. MPs show different capabilities to quantitatively affect IL-12 production; MP2, an 8. 2-kDa MP purified from the culture supernatant of C. neoformans, appears to be the most potent stimulator. Cytochalasin B inhibits both internalization and IL-12 induction by MP. In addition, a drastic reduction of IL-12 was observed when monocytes were cultured in the absence of normal human serum or treated with soluble mannan. Early production of IL-12 promotes early secretion of gamma interferon by T cells but does not influence the magnitude of the MP-induced lymphoproliferative response. Overall our results identify cryptococcal antigens responsible for rapid and potent induction of IL-12 in monocytes. MPs appear to regulate IL-12 secretion by internalization via the endocytic pathway and by interaction with monocyte receptors or serum factors.

Up-regulation of IL-12 in monocytes: a fundamental defect in common variable immunodeficiency

We show that LPS-stimulated circulating CD14-positive monocytes from patients with common variable immunodeficiency (CVID) express a higher proportion of intracellular IL-12-positive cells than monocytes from patients with X-linked agammaglobulinemia or normal subjects. We used four-color flow cytometry and measured IL-12 with an Ab to the p40 subunit following stimulation with LPS. The raised IL-12 is associated with an increased frequency of IFN-gamma-positive T cells, but not of IFN-gamma-positive CD56+ NK cells. These increases in frequency of cytokine-positive cells are due to a decrease in the absolute numbers of circulating monocytes and T cells that are negative for IL-12 and IFN-gamma, respectively. The increased frequency of IL-12-positive monocytes appears to be selective because TNF-alpha was not increased, and is thus unlikely to reflect a general activation. Chronic infection is also unlikely to explain our data since cells from X-linked agammaglobulinemia patients with a similar Ig deficiency do not show these changes. Our data suggest a fundamental abnormality in the IL-12/IFN-gamma circuit in CVID, with up-regulation of IL-12 being the "primary" factor. This imbalance is likely to skew the immune response away from Ab production and also explains the failure of CVID T cells to make Ag-specific memory cells and the chronic inflammatory and granulomatous complications that are a feature of CVID. This disease appears to be a rare example of a polarized Th1-type response and may in part be due to a genetic defect in the control of IL-12 production.

Effect of glutamine on Th1 and Th2 cytokine responses of human peripheral blood mononuclear cells

Decreased glutamine concentrations are found in patients with catabolic stress and are related to susceptibility to infections. In this study, we evaluated the role of glutamine in Th1/Th2 cytokine responses. Peripheral blood mononuclear cells were stimulated with phytohemagglutinin (PHA), live attenuated bacillus Calmette-Guérin (BCG), or measles virus in the presence of different glutamine concentrations. We found that glutamine at an optimal concentration (0.6 mM) significantly enhanced PHA-stimulated lymphocyte proliferation as well as Th1 [interferon-gamma (IFN-gamma) and interleukin-2 (IL-2)] and Th2 cytokine (IL-4 and IL-10) production. In the absence of glutamine, BCG and measles virus elicited minimal lymphocyte proliferation, whereas BCG enhanced Th1 cytokine response and measles virus promoted Th2 cytokine response. Interestingly, addition of glutamine promoted the BCG-elicited Th1 cytokine response (IFN-gamma), but suppressed the measles-induced Th2 cytokine response (IL-10). These results suggest that appropriate glutamine levels may influence host responses to different antigens and microorganisms. Furthermore, predominately Th1, but not Th2, cytokine responses required the presence of optimal concentrations of glutamine.

Induction and regulation of Th1-inducing cytokines by bacterial DNA, lipopolysaccharide, and heat-inactivated bacteria

Th1 immune responses, characterized by production of gamma interferon (IFN-gamma), are associated with protective immunity to viruses and intracellular bacteria. Heat-killed Brucella abortus promotes secretion of Th1-inducing cytokines such as interleukin-12 (IL-12) and IFN-gamma and has been used as a carrier to induce Th1 responses to vaccines. To explore which bacterial constituents could mediate this response and how it is regulated, murine spleen cells were cultured with B. abortus derived DNA, lipopolysaccharide (LPS), or whole killed organisms. Each constituent induced similar, substantial amounts of IL-10. However, only B. abortus and B. abortus DNA induced high levels of IFN-gamma and IL-12. B. abortus and B. abortus DNA-stimulated IL-12 production was maximal by 6 to 18 h, while IL-10 production steadily accumulated over this time period. These kinetics suggested that IL-10 may eventually downmodulate the Th1-like cytokine response to B. abortus and B. abortus DNA, which was confirmed by using neutralizing antibody. In the absence of IL-10, B. abortus LPS induced strong IFN-gamma responses, but IL-12 p70 levels were still undetectable from BALB/c spleen cells. LPS induced IL-12 if the spleen cells were primed with IFN-gamma and IL-10 was neutralized, indicating that LPS can stimulate IL-12 production under the most favorable conditions. Responses to Escherichia coli LPS and DNA mirrored the responses to B. abortus components, suggesting that immune effects observed with these constituents may be generalizable to many microbial species. In vivo experiments demonstrated the same hierarchy of responses for IL-12 production. These findings support the likelihood that microbial components, if used as carriers or adjuvants, can differ substantially in their ability to effect a Th1 response.

Cooperation between Th1 and Th2 cells in a murine model of eosinophilic airway inflammation

We have studied the actions of helper T lymphocyte-1 and -2 (Th1 and Th2) cells in an acute model of eosinophilic airway inflammation by infusing chicken ovalbumin-specific (OVA-specific) Th1 cells, Th2 cells, or both into unsensitized mice and challenging the mice with an OVA aerosol. OVA challenge after infusion of Th1 cells alone resulted in airway inflammation with lymphocytes and monocytes. Challenge after the infusion of Th2 cells alone resulted in minimal inflammation. In contrast, when Th1 and Th2 cells were transferred together, they cooperated to promote a robust eosinophil-predominant inflammatory response. Th1 cells alone were readily recruited to the airways after challenge, but in the absence of Th1 cells, Th2 cells did not accumulate in the airways. When transferred together, both Th1 and Th2 cells, as well as endogenous eosinophils, were effectively recruited. This recruitment was correlated with increased VCAM-1 expression in the medium- and large-sized vessels of the lung and could be inhibited by treating the mice with neutralizing antibodies to TNF-alpha or VCAM-1. These data indicate that Th2 cells require signals in addition to antigen for their effective recruitment to the airways. Th1 cells can provide these signals.

Impaired production of IL-12 in systemic lupus erythematosus. III: deficient IL-12 p40 gene expression and cross-regulation of IL-12, IL-10 and IFN-gamma gene expression

Interleukin 12 (IL-12) is a heterodimer comprising p35 and p40 subunits which are encoded and regulated separately. The authors previously demonstrated deficient IL-12 production in SLE which correlates negatively with disease activity. The present study was designed to determine whether deficiency of IL-12 and excess production of IL-10 and IL-6 in systemic lupus erythematosus (SLE) are due to aberrant regulation at the gene level. Using semiquantitative RT-PCR assay, it was shown that constitutive expression of IL-12 p35 gene is somewhat impaired in SLE compared with controls and that IL-12 p40 mRNA, which was present at low levels in controls, was undetectable in unstimulated SLE peripheral blood mononuclear cells (PBMC). Gene expression of IL-12 p35 and p40 was significantly increased in response to SAC, with significantly lower SAC-induced expression of p40 in SLE patients than controls. SAC-stimulated IL-12 p35 and p40 mRNAs were significantly augmented by interferon gamma (IFN-gamma). Exogenous IL-12 or IFN-gamma significantly inhibited IL-10 gene expression, without affecting IL-6 mRNA or other proinflammatory cytokine mRNA levels. These observations were further confirmed by studies of protein production at the single cell level using ELISPOT assay. Downregulation of IL-12 p40 expression appears to be the cause of IL12 p70 deficiency in SLE. If this defect could be repaired, normalization of IL-12 and IFN-gamma production should reduce excessive IL-10 and prevent pathology.

Regulation of allergic mucosal sensitization by interleukin-12 gene transfer to the airway

Expression of granulocyte macrophage colony-stimulating factor (GM-CSF) in the airway allows allergic sensitization to ovalbumin (OVA) in an experimental protocol that others have shown to induce inhalation tolerance. The ensuing response is characterized by T helper (Th)2 cytokines, marked eosinophilia in the bronchoalveolar lavage fluid (BALF) and the tissue, and goblet-cell hyperplasia. These findings, which underscore the importance of the airway microenvironment in the development of immune responses to airborne antigens, prompted us to investigate whether a Type 1 polarized cytokine milieu in the airway would modulate the allergic sensitization. To this end, we concurrently expressed GM-CSF and interleukin (IL)-12 in the airway, using an adenovirus-mediated gene transfer approach. Coexpression of IL-12 did not prevent the development of an antigen-specific immune inflammatory response, but altered its phenotype. Whereas a similar total cell number was observed in the BALF, airway eosinophilia was abrogated. Histologic evaluation of the tissue corroborated the findings in the BALF and demonstrated that IL-12 coexpression prevented goblet-cell hyperplasia. Expression of IL-12 decreased IL-4 and IL-5 content in the BALF by about 80 and 95%, respectively, and IL-5 in the serum by approximately 80%. In contrast, interferon (IFN)-gamma was increased in both BALF and serum. Similarly, we observed a Th2/Th1 shift in OVA-specific cytokine production in vitro. Recall challenge with OVA in vivo after resolution of the initial inflammatory response demonstrated that the effect of IL-12 was persistent. IL-12-mediated inhibition of airway eosinophilia was mainly IFN-gamma-independent, whereas inhibition of OVA-specific IgE synthesis was IFN-gamma-dependent. Our data underscore the importance of the airway microenvironment in the elicitation of immune responses to environmental antigens.

Bruton’s Tyrosine Kinase Deficiency in Macrophages Inhibits Nitric Oxide Generation Leading to Enhancement of IL-12 Induction

We show that macrophages of X-linked immunodeficient mice with a mutant nonfunctional Bruton’s tyrosine kinase produce less NO than wild-type macrophages in response to a variety of stimuli. Induction of the inducible NO synthase (iNOS) protein, the transcription factor IFN regulatory factor-1 involved in iNOS expression, and the transcription factor STAT-1 involved in regulating IFN regulatory factor-1 induction are all poorer in X-linked immunodeficient than in wild-type macrophages. On the other hand, induction of IL-12 is higher in X-linked immunodeficient than in wild-type macrophages. Macrophage IL-12 induction is enhanced by iNOS inhibitors such as aminoguanidine and thiocitrulline and is inhibited by NO generation via sodium nitroprusside. There is relative enhancement of IFN-γ production by immune T cells from mice immunized under aminoguanidine cover. Our data thus suggest that Bruton’s tyrosine kinase participates in signaling for iNOS induction via IFN regulatory factor-1 in macrophages and that NO is an inhibitor of IL-12 induction.

Anergy, IFN-γ Production, and Apoptosis in Terminal Infection of Mice with Mycobacterium avium

We have followed the course of experimental infection of mice with Mycobacterium avium over an extended period, assessing bacterial numbers and T cell responsiveness. When mice were infected intranasally, bacteria spread to the spleen and liver, but remained in highest numbers in the lungs. Both CD4+ and CD8+ T cells, assayed at any time from 6–28 wk after infection, produced IFN-γ. After initial rapid growth, bacterial numbers slowly increased from ∼107 at 6 wk to more than 5 × 108 at 28 wk, indicating that the resistance mechanisms so generated were not adequate to contain the infection. During infection, apoptosis of both CD4+ and CD8+ T cells, measured immediately ex vivo by staining with Annexin V, increased steadily. With some individual exceptions, there was a close correlation between apoptosis of CD4+ cells and level of IFN-γ production by cultured spleen cells. By 34 wk postinfection, there was an abrupt cessation of IFN-γ production. No IL-4 was detected, ruling out a switch to Th2 profile. Subsequently, bacterial numbers increased still further to &gt;5 × 109 per lung, and the mice lost body weight and would have died if not killed for experimental or humane reasons. The possibility that T cells exposed over this prolonged period to extremely high doses of Ag may become tolerant by a process of terminal differentiation is discussed.

The Interleukin-12–Mediated Pathway of Immune Events Is Dysfunctional in Human Immunodeficiency Virus–Infected Individuals

Interleukin-12 (IL-12) is a potentially critical factor in the immune response against human immunodeficiency virus (HIV) because it is important for regulating proliferation and interferon-γ (IFN-γ) production by T cells and natural killer (NK) cells, antigen presentation and accessory cell function by macrophages and dendritic cells, and cytolytic activities of cytotoxic T-lymphocyte cells and NK cells, which are all functions known to be dysfunctional in patients with acquired immune deficiency syndrome. Peripheral blood mononuclear cells (PBMC) from HIV-infected patients have been previously shown to be deficient in the ability to produce IL-12 in response to the bacterial pathogen Staphylococcus aureus Cowan. In this study, impaired IL-12 production in cells from PBMC of HIV-infected patients compared with healthy donors was observed across a broad panel of stimuli derived from infectious pathogens with or without priming with cytokines such as IFN-γ and IL-4, which amplify the IL-12 induction signal. Analysis of p40 and p35 mRNA accumulation showed that reductions in both subunits contribute to the lower IL-12 secretion of cells from HIV-infected individuals. PBMC from HIV-infected donors also failed to upregulate the IL-12 receptor β2 chain (IL-12Rβ2) in response to mitogenic stimuli. The expression of the IL-12Rβ2 gene could, however, be restored by in vitro exposure to rIL-12. Thus, it is possible that a primary IL-12 defect may lead to secondary deficiencies in expression of the genes for IL-12Rβ2 and IFN-γ, thus amplifying immune deficiency during HIV infection.

Decreased CD40 ligand induction in CD4 T cells and dysregulated IL-12 production during HIV infection

During HIV infection various cytokines are overproduced in early stages, whereas in advanced disease cytokines of the T helper 1 type (e.g. interferon-gamma (IFN-gamma)) are selectively deficient. During antigenic stimulation, the production of type-1 cytokines is enhanced by IL-12, secreted by antigen-presenting cells (APC) after their interaction with activated CD4 T cells. Two factors are essential in this process: priming APC with IFN-gamma and triggering the CD40 receptor on APC by CD40 ligand (CD40L). In view of the importance of this pathway, we compared its regulation in HIV-infected and control subjects. After cross-linking of the T cell receptor (TCR)/CD3 complex, the proportional expression of CD40L was similar on CD4+ T cells from controls and from patients with high circulating CD4 T counts (> 500/microl), but CD40L up-regulation was significantly reduced in patients with more advanced disease. Simultaneous triggering of the costimulatory receptor CD28 on T cells through its natural ligand CD80 partly corrected the CD40L defect in patients with intermediate CD4 T counts (200-500), but not in AIDS patients. Early production of IFN-gamma was preserved in lymphocytes from HIV+ patients. The expression of CD40 on peripheral monocytes from HIV+ subjects was increased in a disease stage-related fashion. Stimulation of mononuclear cells through cell-bound CD40L and soluble IFN-gamma induced significantly higher IL-12 in cultures from patients with > 200 circulating CD4 T cells, whereas IL-12 production was marginally decreased in cultures from patients with < 200 CD4 T cells, compared with healthy control cultures. In conclusion, our data suggest that impaired CD40L induction on CD4 T cells contributes to deficient type-1 responses through decreased IL-12 production in AIDS infection, whereas enhanced CD40-mediated IL-12 production in less advanced stages might contribute to increased levels of various cytokines in early disease

Expression of L-Selectin on Th1 Cells Is Regulated by IL-12

L-selectin has become established as a key molecule in the recirculation of naïve T cells from the blood to peripheral lymph nodes, yet little is known about its role in the migration of effector or memory cells. While differentiating naïve CD4+ T cells into Th1 and Th2 subsets in vitro, it was noted that L-selectin levels were maintained on the Th1 subset of cells. The expression of L-selectin on the Th1 cells appeared to be dependent on the presence of IL-12. Th2 cells, differentiated in the absence of IL-12, failed to maintain L-selectin expression. Coculture with IL-12, IL-18, IL-4, TNF-α, or IFN-α, -β, or -γ demonstrated a dependence on IL-12 alone for L-selectin expression. In addition, the inclusion of heat-killed Listeria monocytogenes in the cultures also maintained L-selectin expression on the Th1 cells. In all cultures, the maintenance of L-selectin on the T cell surface could be blocked by the inclusion of anti-IL-12 Abs. Analysis of the mRNA levels for L-selectin in T cells, differentiated in the presence or absence of IL-12, showed that the cytokine appears to exert its effect on L-selectin at the transcriptional level. Given the key role played by IL-12 in the differentiation of naïve T cells into the Th1 subset, the observation that IL-12 can also regulate L-selectin expression has implications for the migration of Th1 effector cells both through the lymphatic system and to sites of inflammation.

Use of recombinant viruses to deliver cytokines influencing the course of experimental bacterial infection

The feasibility of using viral constructs expressing cytokine genes to influence the course of bacterial infection was tested in mice. The mice were first infected with vaccinia or fowlpox viruses expressing the cytokine of interest, then challenged with the facultative intracellular bacterial pathogen Listeria monocytogenes. The course of infection was assessed by subsequent bacterial counts. Expression of IFN-gamma or TNF was protective. Vaccinia virus was more efficient at delivering IFN-gamma-mediated protection than was fowlpox virus, which is unable to proliferate in mammalian cells. The effect of vaccinia-IFN-gamma was more apparent in the liver, where vaccinia proliferates to high titres (> 109), than in the spleen, where only 103 vaccinia were isolated. Vaccinia virus expressing IL-4 exacerbated infection. Interleukin-4 exacerbation was T cell independent and was reflected in the failure of macrophage activation, possibly due to suppression of NK cells, which are a source of IFN-gamma early in infection. The clear indication of protection by some cytokines in this prophylactic model appears to justify further study of the therapeutic effects of cytokine-expressing viruses in chronic bacterial infections, especially where a cytokine defect is suspected.

Delayed Clearance of Filarial Infection and Enhanced Th1 Immunity Due to Modulation of Macrophage APC Functions in xid Mice

Bruton’s tyrosine kinase (Btk) mutant CBA/N mice show delayed clearance of injected microfilaria (mf) compared with wild-type CBA/J mice. Anti-mf T cells from CBA/N mice make relatively more IFN-γ than those from CBA/J mice. The anti-mf T cell proliferative responses are also greater in CBA/N mice. This CBA/N immune phenotype is not restricted to filarial Ags, because immunization with pure proteins also yields T cell responses of greater proliferative magnitude skewed away from Th2 cytokines in CBA/N compared with CBA/J mice. The increased magnitude of CBA/N T cell proliferative responses is reflected in increases in both precursor frequencies and clonal burst sizes of responding Ag-specific T cells, and is independent of the source of re-stimulating APCs. Transfer of CBA/J peritoneal resident cells (PRCs) into CBA/N mice before pure protein immunization leads to a wild-type immune phenotype in the recipient CBA/N mice, with a reduction in the proliferative response and a relative decrease in the IFN-γ produced. When wild-type PRC subpopulations are similarly transferred, the wild-type immune phenotype is transferred by macrophages rather than by B cells. Transfer of wild-type PRCs into CBA/N mice before injection of mf also causes similar changes in the anti-mf T cell responses and enhances the clearance of mf. Thus, Btk is involved in critical macrophage APC functions regulating priming of T cells, and can modulate these responses in pathophysiologically relevant fashion in vivo.

Susceptibility or resistance to Leishmania infection is dictated by the macrophages evolved under the influence of IL-3 or GM-CSF

Although enhanced monocytopoiesis is a hallmark of leishmaniasis, its significance in determining the course of the disease has not been addressed. While the number of granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting cells increases in the draining lymph nodes in a resistant mouse strain (C57BL/6) during disease, in a susceptible strain (BALB/c) the number of interleukin-3 (IL-3)-secreting cells increases. Treatment of BALB/c mice with anti-IL-3 antibody significantly reduces the disease score. Bone marrow macrophages derived under stimulation with IL-3 (IL-3-Mphi) or GM-CSF (GM-Mphi) differ functionally. GM-Mphi are significantly more responsive to IFN-gamma-induced augmentation and more refractory to IL-4-mediated suppression of anti-leishmanial activity than IL-3-Mphi. LPS-induced IL-12 and TNF-alpha secretion by both the susceptible and resistant strain-derived macrophage subsets are down-regulated. Despite down-regulation of IL-12 secretion, GM-Mphi favor expansion of IFN-gamma-secreting cells and IL-3-Mphi favor IL-6-dependent expansion of the IL-4-secreting Th subset. Adoptive transfer of leishmanial antigen-pulsed IL-3-Mphi and GM-Mphi prior to infection either aggravated or reduced the disease score, respectively, in BALB/c mice. Anti-IL-6 treatment reverted the Th subset profile not only in vitro but also in vivo, resulting in a reduced disease score in both infected BALB/c mice and IL-3-Mphi recipients. The disease score in IL-3-Mphi recipients is also reduced significantly after anti-IL-4 treatment.

Innate and adaptive immune responses co-operate to protect cattle against Theileria annulata

For many years it was assumed that Theileria annulata resembled T. parva, parasitizing lymphocytes and causing lymphoproliferative disease, with the two species being controlled by similar protective immune responses. Patricia Preston et al. here review the evidence that has led to a different view of T. annulata. It is now thought that the schizonts of T. annulata inhabit macrophages and B cells, and that tropical theileriosis is not a lymphoproliferative disease. Both innate and adaptive responses contribute to recovery from infection and resistance to challenge and cytokines produced by infected and uninfected cells influence the outcome of infection. Partial protection has been stimulated recently by defined recombinant antigens; efficacy depended upon the delivery system.

Interleukin 10-mediated immunosuppression by a variant CD4 T cell epitope of Plasmodium falciparum

The immunodominant CD4 T cell epitope region, Th2R, of the circumsporozoite protein of Plasmodium falciparum is highly polymorphic. Such variation might be utilized by the parasite to escape from or interfere with CD4 T cell effector functions. Here, we show that costimulation with naturally occurring altered peptide ligands (APL) can induce a rapid change from IFNgamma production to the immunosuppressive mediator interleukin 10 (IL-10). This mechanism may contribute to the low levels of T cell responses observed to this pathogen in malaria-endemic areas.

Bacterium-dependent induction of cytokines in mononuclear cells and their pathologic consequences in vivo

Viridans streptococci are a heterogeneous group of gram-positive bacteria that are normal inhabitants of the mouth. These organisms are thought to contribute significantly to the etiology of infective endocarditis, although recently they have been implicated in serious infections in other settings. Another group of oral bacteria, gram-negative anaerobes, is associated with chronic dental infections, such as periodontal diseases or endodontic lesion formation. We evaluated the ability of the oral pathogens Streptococcus mutans and Porphyromonas endodontalis to induce a pathogenic response in vivo, with the goal of quantifying the inflammatory response in soft tissue by measuring leukocyte recruitment and hard tissues by measuring osteoclastogenesis. S. mutans induced a strong inflammatory response and was a potent inducer of osteoclast formation, while P. endodontalis was not. To further study the mechanisms by which P. endodontalis and S. mutans elicit significantly different levels of inflammatory responses in vivo, we tested the capacity of each to induce production of cytokines by mononuclear cells in vitro. S. mutans stimulated high levels of interleukin-12 (IL-12), gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha), all of which are associated with inflammation, enhanced monocyte function, and generation of a Th1 response. In contrast, P. endodontalis stimulated production of IL-10 but not of TNF-alpha, IL-12, or IFN-gamma. These results demonstrate that oral pathogens differ dramatically in their abilities to induce inflammatory and immunoregulatory cytokines. Moreover, there is a high degree of correlation between the cytokine profile induced by these bacteria in vitro and their pathogenic capacity in vivo.

Susceptibility of B-cell deficient C57BL/6 (microMT) mice to Neospora caninum infection

Neospora caninum is a coccidian parasite of veterinary importance by causing abortion or stillbirth in cattle among other problems in diverse animal species. We assessed an experimental murine model for its suitability to study the immune response to N. caninum infection. Thus, wild-type (wt) C57BL/6 mice and B-cell (and consequently antibody)-deficient microMT mice were infected with N. caninum tachyzoites and sacrificed at days 10, 24 and 29-44 post infection (dpi). Various organs were collected for parasitological and pathological analysis, spleen and serum for immunological investigations. Splenocytes were in vitro-stimulated with N. caninum (NC)- and T. gondii-antigens for assessing T cell proliferation and cytokine production. While wt mice were resistant to disease, microMT mice died starting from 29 dpi onwards. Histological examination of brain tissue from microMT mice exhibited a high infection intensity with multifocal necrotic cerebral lesions, which were absent in the brains of wt mice. NC antigen-stimulated spleen cells of both wt and microMT mice infected with N. caninum showed a marked proliferative depression at 10 dpi. At 24 dpi, this immunosuppression was still maintained in microMT mice whereas it was restored in wt mice. Stimulated splenocytes of infected microMT mice secreted significantly less IFN-gamma and less IL-10 than corresponding wt splenocytes. For IL-10, this difference increased with time. The susceptibility of microMT mice appeared associated to B-cell deficiency, allowing the persistent spread of the parasite causing immunosuppression and finally resulting in a lethal outcome of infection.

IL-12, IFN-γ, and T Cell Proliferation to Measles in Immunized Infants

Measles infection in infants is associated with severe complications, and secondary infections are attributed to generalized immunosuppression. Measles binding to its monocyte receptor down-regulates IL-12 which is expected to diminish Th1-like cytokine responses, including IFN-γ. Whether young infants can be immunized effectively against measles is an important public health issue. We evaluated Ag-specific IL-12, IFN-γ, and T cell responses of infants at 6 (n = 60), 9 (n = 46), or 12 mo (n = 56) of age and 29 vaccinated adults. IL-12 and IFN-γ release by PBMC stimulated with measles Ag increased significantly after measles immunization in infants. IL-12 and IFN-γ concentrations were equivalent in younger and older infants, but IL-12 concentrations were significantly lower in infants than in adults (p = 0.04). IL-12 production by monocytes was down-regulated by measles; the addition of recombinant human IL-12 enhanced IFN-γ production by PBMC stimulated with measles Ag, but infant T cells released significantly less IFN-γ than adult T cells under this condition. Of particular interest, the presence of passive Abs to measles had no effect on the specific T cell proliferation or IFN-γ production after measles stimulation. Cellular immunity to measles infection and vaccination may be limited in infants compared with adults as a result of less effective IFN-γ and IL-12 production in response to measles Ags. These effects were not exaggerated in younger infants compared with effects in infants who were immunized at 12 mo. In summary, infant T cells were primed with measles Ag despite the presence of passive Abs, but their adaptive immune responses were limited compared with those of adults.

IL-4 Inhibits the Production of TNF-α and IL-12 by STAT6-Dependent and -Independent Mechanisms

IL-4 promotes allergic responses and inhibits the production of proinflammatory cytokines by monocytes and macrophages. The promotion of allergic responses by IL-4 has been shown to be absolutely dependent on the transcription factor STAT6. We report here that the inhibitory effects of IL-4 on the production of TNF-α or IL-12 by macrophages had both STAT6-dependent and -independent components, depending on the stimuli. IL-4 failed to inhibit the release of TNF-α or IL-12 from STAT6 null macrophages stimulated with LPS alone. However, IL-4 still induced significant inhibition of the production of TNF-α and IL-12 from STAT6 null macrophages that were stimulated with the more physiologically relevant combination of LPS and IFN-γ. These data show that STAT6 is required for the IL-4-mediated inhibition of the production of TNF-α and IL-12 stimulated by LPS alone, but that IL-4 also activates distinct, STAT6 independent mechanism(s) that inhibit the IFN-γ-mediated enhancement of IL-12 and TNF-α production.

Differential Cytokine and Chemokine Gene Expression by Human NK Cells Following Activation with IL-18 or IL-15 in Combination with IL-12: Implications for the Innate Immune Response

NK cells constitutively express monocyte-derived cytokine (monokine) receptors and secrete cytokines and chemokines following monokine stimulation, and are therefore a critical component of the innate immune response to infection. Here we compared the effects of three monokines (IL-18, IL-15, and IL-12) on human NK cell cytokine and chemokine production. IL-18, IL-15, or IL-12 alone did not stimulate significant cytokine or chemokine production in resting NK cells. The combination of IL-18 and IL-12 induced extremely high amounts of IFN-γ protein (225 ± 52 ng/ml) and a 1393 ± 643-fold increase in IFN-γ gene expression over those in resting NK cells. IL-15 and IL-12 induced less IFN-γ protein (24 ± 10 ng/ml; p &lt; 0.007) and only a 45 ± 19-fold increase in IFN-γ gene expression over those in resting NK cells. The CD56bright NK cell subset produced significantly more IFN-γ following IL-18 and IL-12 compared with CD56dim NK cells (p &lt; 0.008). However, the combination of IL-15 and IL-12 was significantly more potent than that of IL-18 and IL-12 for NK cell production of IL-10, macrophage inflammatory protein-1α, macrophage inflammatory protein-1β, and TNF-α at the protein and transcript levels. Granulocyte-macrophage CSF was optimally induced by IL-15 and IL-18. Resting CD56+ NK cells expressed IL-18R transcript that was up-regulated by IL-12 or IL-15. Our results show that distinct cytokine and chemokine patterns are induced in NK cells in response to different costimulatory signals from these three monokines. This suggests that NK cell cytokine production may be governed in part by the monokine milieu induced during the early proinflammatory response to infection and by the subset of NK cells present at the site of inflammation.

Human cytomegalovirus, MHC class I and inhibitory signalling receptors: more questions than answers

The human cytomegalovirus UL18 protein, an MHC class I homologue, has been shown to bind to leucocyte immunoglobulin-like receptor (LIR)-1, a member of a family of nine closely related immunoglobulin superfamily receptors expressed on leucocytes. The LIRs are related to the natural killer (NK)-cell immunoglobulin-like receptors and to several other immunoreceptors. Three groups of LIR molecules have been defined: those containing cytoplasmic domain inhibitory signalling motifs, those with short cytoplasmic domains and a charged residue within the transmembrane domain, and a secreted molecule. LIR-1 and LIR-2 bind to a broad spectrum of cellular MHC class I antigens, including HLA-A, -B and -C alleles. LIR-2 is expressed by all monocytes and dendritic cells, whereas LIR-1 is additionally expressed by B cells and subsets of T and NK cells. Upon tyrosine phosphorylation, LIR-1 and LIR-2 associate with the tyrosine phosphatase, SHP-1, and have been shown to inhibit Fc gamma RI signalling when co-crosslinked in monocytes. Evidence for and against a role of UL18 as an inhibitor of NK-cell function is discussed, as are possible functional outcomes of UL18-LIR-1 interactions in monocytic cells.

CD40 ligation prevents Trypanosoma cruzi infection through interleukin-12 upregulation

Because of the critical role of the CD40-CD40 ligand (CD40L) pathway in the induction and effector phases of immune responses, we investigated the effects of CD40 ligation on the control of Trypanosoma cruzi infection. First, we observed that supernatants of murine spleen cells stimulated by CD40L-transfected 3T3 fibroblasts (3T3-CD40L transfectants) prevent the infection of mouse peritoneal macrophages (MPM) by T. cruzi. This phenomenon depends on de novo production of nitric oxide (NO) as it is prevented by the addition of N-nitro-L-arginine methyl ester, a NO synthase inhibitor. NO production requires interleukin (IL)-12-mediated gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) synthesis as demonstrated by inhibition experiments using neutralizing anti-IL-12, anti-IFN-gamma, and anti-TNF-alpha monoclonal antibodies (MAb). We found that an activating anti-CD40 MAb also directly stimulates IFN-gamma-activated MPM to produce NO and thereby to control T. cruzi infection. To determine the in vivo relevance of these in vitro findings, mice were injected with 3T3-CD40L transfectants or 3T3 control fibroblasts at the time of T. cruzi inoculation. We observed that in vivo CD40 ligation dramatically reduced both parasitemia and the mortality rate of T. cruzi-infected mice. A reduced parasitemia was still observed when the injection of 3T3-CD40L transfectants was delayed 8 days postinfection. It was abolished by injection of anti-IL-12 MAb. Taken together, these data establish that CD40 ligation facilitates the control of T. cruzi infection through a cascade involving IL-12, IFN-gamma, and NO.

IL-5 and Eosinophils Are Essential for the Development of Airway Hyperresponsiveness Following Acute Respiratory Syncytial Virus Infection

Viral respiratory infections can cause bronchial hyperresponsiveness and exacerbate asthma. In mice, respiratory syncytial virus (RSV) infection, which induces an immune response dominated by IFN-γ, results in airway hyperresponsiveness (AHR) and eosinophil influx into the airways, both of which are prevented by pretreatment with anti-IL-5 Ab. To delineate the role of IL-5, IL-4, and IFN-γ in the development of RSV-induced AHR and lung eosinophilia, we tested the ability of mice deficient in each of these cytokines to develop these symptoms of RSV infection. Mice deficient in either IL-5, IL-4, or IFN-γ were administered infectious RSV intranasally, and 6 days later, airway responsiveness to inhaled methacholine was assessed by barometric body plethysmography, and numbers of lung eosinophils and production of IFN-γ, IL-4, and IL-5 by mononuclear cells from peribronchial lymph nodes were monitored. RSV infection resulted in airway eosinophilia and AHR in both IL-4- and IFN-γ-deficient mice, but not in IL-5-deficient mice. Reconstitution of IL-5-deficient mice with IL-5 restored these responses and enhanced the responses in IL-4-deficient mice. Anti-VLA-4 (very late Ag-4) treatment prevented lung eosinophilia and AHR following RSV infection and IL-5 reconstitution. We conclude that in response to RSV, IL-5 is essential for the influx of eosinophils into the lung and that eosinophils in turn are critical for the development of AHR. IFN-γ and IL-4 are not essential for these responses to RSV infection.