Inhibition of CCR5 Expression by IL-12 Through Induction of β-Chemokines in Human T Lymphocytes

IL-12 induces initiation of the differentiation of naive CD4+ T lymphocytes into Th1 cells and is important for the control of cell-mediated immunity. β-Chemokines serve to attract various types of blood leukocytes to sites of infection and inflammation. The specific receptor for the β-chemokines (macrophage-inflammatory protein (MIP)-1α, MIP-1β, and RANTES), CCR5, also functions as the primary coreceptor for macrophage-tropic isolates of HIV-1. IL-12, but not IL-4, IL-10, or IL-13, now has been shown to down-modulate the surface expression of CCR5 induced by IL-2 on both CD4+ and CD8+ T lymphocytes. Decreased CCR5 surface expression was not secondary to transcriptional inhibition, given that CCR5 mRNA was enhanced in cells cultured in IL-12/IL-2 compared with those cultured in IL-2 only. The effect of IL-12 in down-modulation of CCR5 surface expression was shown to be mediated by soluble factors secreted from the T cells. Rapid and transient intracellular Ca2+ mobilization was induced in monocytes by IL-12-induced supernatants, which desensitized the response of monocytes to MIP-1α, but not their response to stromal cell-derived factor-1α. Neutralization with specific Abs identified these factors as MIP-1α and MIP-1β from most donors. IL-4, IL-10, IFN-γ, and IL-18 primarily inhibited MIP-1β secretion and also weakly suppressed MIP-1α secretion. HIV-1 replication was inhibited in IL-2/IL-12-containing cultures that correlated with chemokine and chemokine-receptor levels. These data suggest that the effects of IL-12 on β-chemokine production and chemokine-receptor expression may contribute to the immunomodulatory activities of IL-12 and may have potential therapeutic relevance in controlling HIV-1 replication.

Specific Activated T Cells Regulate IL-12 Production by Human Monocytes Stimulated with Cryptococcus neoformans

IL-12 production mediated by a T cell-independent and/or T cell-dependent pathway was investigated in human monocytes responding to Cryptococcus neoformans. The data of this study showed that: 1) appreciable levels of IL-12 were observed when freshly isolated monocytes were exposed to acapsular C. neoformans or Candida albicans and secretion occurred within 24–48 h of incubation; 2) monocytes alone were poor producers of IL-12 when stimulated with encapsulated C. neoformans; 3) the presence of specific anti-glucuronoxylomannan mAb favored IL-12 secretion and Fc cross-linking could play a role; 4) monocytes were able to secrete consistent levels of IL-12 when cultured with activated T cells responding to C. neoformans; 5) the maximum secretion of IL-12 was observed at 5–7 days of culture and was strongly regulated by the presence of endogenous IFN-γ; and 6) the interaction between CD40 on monocytes and CD40 ligand on activated T lymphocytes responding to C. neoformans played a critical role in IL-12 secretion. These data highlight the mechanisms of IL-12 production by human monocytes exposed to C. neoformans, indicating a possible biphasic secretion of IL-12, dependent on the direct effect of fungal insult, and characterized by consistent secretion of IL-12 that is dependent on the interaction of CD40 with the CD40 ligand expressed on activated T cells responding to C. neoformans.

The Inflammatory Response to Nonfatal Sindbis Virus Infection of the Nervous System Is More Severe in SJL Than in BALB/c Mice and Is Associated with Low Levels of IL-4 mRNA and High Levels of IL-10-Producing CD4+ T Cells

SJL mice are susceptible to inflammatory autoimmune diseases of the central nervous system (CNS), while BALB/c mice are relatively resistant. To understand differences in immune responses that may contribute to autoimmune neurologic disease, we compared the responses of SJL and BALB/c mice to infection with Sindbis virus, a virus that causes acute nonfatal encephalomyelitis in both strains of mice. Clearance of virus was similar, but SJL mice developed a more intense inflammatory response in the brain and spinal cord and inflammation persisted for several weeks. Analysis of lymphocytes isolated from brains early after infection showed an absence of NK cells in SJL mice, while both strains of mice showed CD4+ and CD8+ T cells. During the second week after infection, CD4+ T cells increased in SJL mice and the proportion of CD8+ T cells decreased, while the opposite pattern was seen in BALB/c mice. Expression of IL-10 mRNA was higher and IL-4 mRNA was lower in the brains of infected SJL than in BALB/c mice, while expression of the mRNAs of IL-6, IL-1β, TNFα, and the Th1 cytokines IL-2, IL-12, and IFN-γ was similar. Lymphocytes isolated from the CNS of SJL mice produced large amounts of IL-10. CNS lymphocytes from both strains of mice produced IFN-γ in response to stimulation with Sindbis virus, but not in response to myelin basic protein. These data suggest that IL-10-producing CD4+ T cells are differentially recruited to or regulated within the CNS of SJL mice compared with BALB/c mice infected with Sindbis virus, a characteristic that may be related to low levels of IL-4, and is likely to be involved in susceptibility of SJL mice to CNS inflammatory diseases.

Antibodies Against IL-12 Prevent Superantigen-Induced and Spontaneous Relapses of Experimental Autoimmune Encephalomyelitis

Immunization of (PL/J × SJL/J)F1 mice with myelin basic protein (MBP) induces relapsing experimental autoimmune encephalomyelitis (EAE). Relapses occur 7 to 10 days after recovery from the initial paralysis. Staphylococcal enterotoxins (SE) A or B, administered after recovery from the initial paralysis, induce immediate relapses. IL-12 is involved in the induction of EAE. Here, we show that SEA and SEB induce IL-12 in splenocytes from (PL/J × SJL/J)F1 mice in vitro and increase the level of IL-12 in the sera of mice treated with these superantigens. IL-12 administration mimics SE in inducing spontaneous relapses and in enhancing the severity and frequency of spontaneous relapses. IL-12 neutralization blocks SE-induced and subsequent relapses of EAE, and, when instituted after recovery from the initial attack, prevents spontaneous relapse. This is the first report of prevention of relapses of EAE with anti-IL-12 Ab, an approach which may prove useful in the prevention of exacerbations in multiple sclerosis.

IFN-α Priming of Human Monocytes Differentially Regulates Gram-Positive and Gram-Negative Bacteria-Induced IL-10 Release and Selectively Enhances IL-12p70, CD80, and MHC Class I Expression

Administration of IFN-γ and IFN-α may protect or induce autoimmune diseases. Although the in vitro regulation of monokine secretion by IFN-γ have been extensively studied, the regulatory function of IFN-α has not yet been elucidated. We compared IFN-α and IFN-γ, added alone or simultaneously before bacterial stimulation, for the control of monokine release and the expression of costimulatory molecules by human monocytes. Our data show that: 1) IFN-α primes monocytes for increased production of IL-10 in response to Staphylococcus aureus Cowan I strain (SAC) but not to LPS, leading to a lack of IFN-α priming for TNF-α secretion; 2) pretreatment of monocytes with IFN-α inhibits LPS- or SAC-induced IL-12p40 production but unexpectedly enhances the release of the biologically active form of IL-12 (IL-12p70); 3) IFN-α and IFN-γ exert an antagonistic effect on LPS- and SAC-induced IL-10 as well as IL-12p40 release, whereas they further enhance IL-12p70 production when added simultaneously; 4) in contrast to IFN-α, IFN-γ primes monocytes to enhance LPS- or SAC-induced TNF-α and IL-12 production, but surprisingly, it increases IL-10 production by monocytes following LPS but not SAC stimulation; and finally, 5) IFN-α pretreatment selectively up-regulates CD80 and MHC class I expression on monocytes. It is proposed that the outcome of the immune response at the site of inflammation may depend on both the type of bacterial injury (Gram-positive or -negative) and of locally produced IFNs, and that the differential and opposite effects of type I and type II IFNs on monocytes may account for the beneficial or detrimental effects of IFN-α therapy.

Active Wegener’s Granulomatosis Is Associated with HLA-DR+ CD4+ T Cells Exhibiting an Unbalanced Th1-Type T Cell Cytokine Pattern: Reversal with IL-10

Wegener’s granulomatosis (WG) is a granulomatous vasculitis that affects the upper respiratory tract, lung, and kidney. Since T cells make up a significant proportion of cells infiltrating granulomatous lesions in WG, we investigated the proliferative response and cytokine profile of T cells from these patients. PBMCs were isolated from 12 patients with active WG, 7 patients with inactive disease, and 12 healthy normal donors. PBMCs from clinically active WG patients exhibited increased proliferation following stimulation with either PMA/ionomycin or anti-CD2 and anti-CD28, when compared with normal donors. In addition, these PBMCs exhibited increased secretion of IFN-γ, but not of IL-4, IL-5, or IL-10. Furthermore, TNF-α production from PBMCs and CD4+ T cells isolated from patients with WG was elevated, when compared with healthy donors. In further studies, we investigated the ability of WG patients’ monocytes to produce IL-12 and showed that both inactive and active patients produced increased amounts of IL-12. Finally, the in vitro IFN-γ production by WG PBMC is inhibited in a dose-dependent manner by exogenous IL-10. These data suggest that T cells from WG patients overproduce IFN-γ and TNF-α, probably due to dysregulated IL-12 secretion, and that IL-10 may therefore have therapeutic implications for this disease.

Production of IL-10 by Human Natural Killer Cells Stimulated with IL-2 and/or IL-12

Human NK cell activity can be augmented in vitro by stimulation with IL-2 or IL-12, both of which also induce the production of IFN-γ, TNF-α, and granulocyte-macrophage CSF by NK cells. For the first time, we demonstrate that freshly purified NK cells stimulated with IL-2 proliferated and produced IL-10 in a dose-dependent manner. IL-10 mRNA expression, as detected by semiquantitative reverse transcription-PCR, reached peak levels at 24 h. IL-10 protein was detectable on day 2 and further increased on days 3 and 6 as measured by ELISA. However, IL-12 alone induced neither substantial proliferation nor detectable IL-10 production by fresh NK cells, but it synergized with IL-2 in inducing IL-10 mRNA expression and protein synthesis. IL-10 production by activated NK cells was confirmed by intracytoplasmic cytokine staining by three-color immunofluorescence of CD16+ and/or CD56+ NK cells with anti-IL-10 antibody. IL-10 production by NK cells was further confirmed in the NK-like cell line, YT, which constitutively expressed IL-10 mRNA and protein. IL-12 alone did not induce NK proliferation, but it inhibited IL-2-induced proliferation. Neutralization of endogenously produced IL-10 with anti-IL-10 antibodies did not overcome the inhibition of IL-2-induced proliferation by IL-12. Together, these results demonstrate that IL-2 and IL-12 synergize to induce IL-10 production by human NK cells and that IL-12 inhibits IL-2 induced NK cell proliferation by an IL-10-independent mechanism.

Corticosteroids Enhance the Capacity of Macrophages to Induce Th2 Cytokine Synthesis in CD4+ Lymphocytes by Inhibiting IL-12 Production

We investigated the effects of corticosteroids on IL-12 production by mouse splenic adherent cells and the subsequent capacity of these cells to induce cytokine production by CD4+ T cells. To distinguish the effects of corticosteroids on APCs from those on T cells, only the APCs and not the T cells were exposed to corticosteroids. Treatment of splenic adherent cells with dexamethasone greatly inhibited production of IL-12, a cytokine known to enhance IFN-γ synthesis and decrease IL-4 synthesis by CD4+ T cells. The reduction in IL-12 production by corticosteroid-treated macrophages decreased their ability to induce IFN-γ and increased their ability to induce IL-4 synthesis in Ag-primed CD4+ T cells. Splenic adherent cells from mice treated in vivo with dexamethasone also displayed a reduced capacity to produce IL-12. These results help to resolve previous conflicting observations regarding the effects of corticosteroids on cytokine production by T cells, and indicate that while corticosteroids may directly inhibit Th1 and Th2 cytokine production in T cells, corticosteroids, by reducing IL-12 production in APCs, have the potential to indirectly enhance Th2 cytokine synthesis. Therefore, treatment of diseases such as allergy with chronic corticosteroids may indirectly exacerbate the course of the disease, which is caused primarily by the overproduction of Th2 cytokines in allergen-specific CD4+ T cells.

Alloantigen-Reactive Th1 Development in IL-12-Deficient Mice

IL-12p70, a 70- to 75-kDa heterodimer consisting of disulfide-bonded 35-kDa (p35) and 40-kDa (p40) subunits, enhances Th1 development primarily by its ability to induce IFN-γ production by NK and Th1 cells. Although homodimers of the p40 subunit of IL-12 are potent IL-12 receptor antagonists in some systems, we have reported that p40 homodimer may accentuate alloreactive CD8+ Th1 function. To test the role of endogenously produced p40 in alloimmunity, Th1 development was assessed in either IL-12 p35 knockout (p35−/−) mice, the cells of which are capable of secreting p40, or p40 knockout (p40−/−) mice. Compared with IL-12 wild-type controls, splenocytes obtained from both p35−/− and p40−/− mice produced markedly less IFN-γ after in vitro stimulation with Con A or alloantigens. Interestingly, in vivo-sensitized Th1 were detected in both p35−/− and p40−/− cardiac allograft recipients. However, in vivo Th1 development was enhanced in p35−/− recipients compared with p40−/− animals, suggesting that endogenous p40 produced in p35−/− mice may stimulate alloreactive Th1. Indeed, neutralizing endogenous p40 with anti-IL-12 p40 mAb reduced Th1 development in p35−/− allograft recipients to that seen in p40−/− mice. To determine whether Th1 development that occurred in the absence of IL-12p70 and p40 required IFN-γ, p40−/− allograft recipients were treated with anti-IFN-γ mAb. Neutralizing IFN-γ did not inhibit in vivo Th1 development in p40−/− recipients and resulted in a unique pathology of rejection characterized by vascular thromboses. Collectively, these data suggest that 1) endogenous p40 may substitute for IL-12p70 in alloantigen-specific Th1 sensitization in vivo and 2) in vivo alloreactive Th1 development may occur independent of IL-12 and IFN-γ, suggesting an alternate Th1-sensitizing pathway.