T4 cell activation by immobilized phytohemagglutinin: differential capacity to induce IL-2 responsiveness and IL-2 production

Soluble mitogens, such as PHA induce accessory cell (AC)-dependent T cell proliferation. One function of the AC is to create a stimulatory matrix. Therefore, experiments were carried out to determine whether PHA immobilized onto microtiter plates could stimulate T cells in the absence of AC. Peripheral blood T4 cells were cultured under limiting dilution conditions with either soluble or immobilized PHA with or without rIL-1 beta, rIL-2, r-TNF-alpha, an anti-CD28 mAb (9.3), or irradiated EBV-transformed B cells as AC. The frequency of proliferating T4 cells was assessed by examining wells microscopically, and the frequency of T4 cells producing IL-2 was assessed by examining the ability of supernatants to support CTLL-2 proliferation. The percentage of T4 cells growing and producing IL-2 was determined by a maximum likelihood procedure. Immobilized, but not soluble, PHA induced a mean of 20.0 +/- 2.6% of T4 cells to grow in the complete absence of AC in medium supplemented with rIL-2. Whereas rIL-1 beta, rTNF-alpha, and 9.3 were unable to support T4 cell growth in the absence of rIL-2, each enhanced the percentage of T4 cells responding to immobilized PHA in the presence of rIL-2. In contrast, both soluble and immobilized PHA were unable to induce T4 cell IL-2 production in the absence of AC, even when cultures were supplemented with rIL-1 beta or 9.3. In the presence of AC, a small percentage of T4 cells (5.4 to 11.7%) was stimulated to produce detectable amounts of IL-2 by either immobilized or soluble PHA. Moreover, in the presence of AC, a very small population (approximately 1%) of PHA-stimulated T4 cells proliferated without supplemental rIL-2. The data indicate that a matrix of immobilized PHA is sufficient for some T4 cells to be activated to respond to IL-2, whereas others require additional signals provided by rIL-1 beta, rTNF alpha, 9.3, or AC. In contrast, neither soluble nor immobilized PHA is sufficient to induce T cell IL-2 production. This response requires signals provided by intact AC.     

Enhancement of IL-2-induced T cell proliferation by a novel factor(s) present in murine spleen dendritic cell-T cell culture supernatants

The mechanism(s) underlying the potent accessory cell function of dendritic cells (DC) remains unclear. The possibility was considered that a soluble factor(s) released during the interaction of DC and T cells might contribute to the potent T cell activating function of DC. Culture supernatants were generated from mixtures of murine spleen DC and periodate-treated spleen T cells and were examined for the presence of known cytokine activities and factors capable of enhancing T cell responsiveness to IL-2. Serum-free supernatants from 24 h DC-T cell co-cultures exhibited high levels of IL-2, detectable levels of IL-3, and negligible levels of IL-1, -4, -5, -6, and TNF. A factor(s) was also identified with an apparent Mr of 12.5 to 17.0 kDa, henceforth designated IL-2 enhancing factor (IL-2EF), which enhanced the IL-2-induced proliferation of murine thymocytes, CTLL, and HT-2 cells by approximately three- to fourfold. This enhancement was also observed in the presence of neutralizing antibodies to murine IL-1 alpha, -1 beta, -3, -4, -5, -6, granulocyte-macrophage (GM)-CSF, TNF, and IFN-gamma. However, IL-2EF failed to enhance: 1) the activity of IL-1, -3, -4, -5, or -6 on cells responsive to these cytokines; 2) IL-2-augmented, IL-5-induced BCL1 proliferation; and 3) either PHA- or Con A-stimulated thymocyte proliferation. Moreover, neither IFN-gamma nor GM-CSF exhibited IL-2EF activity. When DC and T cells were cultured separately (after an initial 12 h co-culture period), IL-2EF activity resided predominantly in the T cell-derived supernatants. These and other data indicate that IL-2EF, a heat-labile T cell-derived 12.5 to 17.0 kDa protein, is distinct from IL-1 alpha, -1 beta, -2, -3, -4, -5, -6, TNF, IFN-gamma, GM-CSF, and previously described factors that co-stimulate thymocyte proliferation in the presence of Con A or PHA. It is suggested that IL-2EF functions to specifically enhance IL-2-driven T cell proliferation and contributes to the potent activation of T cells induced by DC.     

Induction of interleukin-1 in human monocytes by the superantigen staphylococcal enterotoxin A requires the participation of T cells

Nanogram quantities of the bacterial superantigen Staphylococcal Enterotoxin A (SEA) induced significant amounts of extracellular IL-1 alpha and IL-1 beta in human peripheral blood mononuclear cells. Induction of maximal IL-1 alpha and IL-1 beta levels by lipopolysaccharide (LPS) required microgram quantities. LPS induced detectable extracellular IL-1 content within 3-6 hr and maximal levels were detected already after 12 hr. Induction of IL-1 production by SEA showed a delayed release with peak values after 24-48 hr. IL-1 beta was the major species of IL-1 seen in both SEA- and LPS-stimulated culture supernatants. SEA was in general a relatively stronger inducer of extracellular IL-1 alpha than LPS. SEA-induced extracellular IL-1 production in human monocytes was entirely dependent on the presence of T cells, whereas addition of T cells to LPS-stimulated purified human monocytes only marginally enhanced the extracellular IL-1 production. The capacity to induce extracellular IL-1 production in monocytes in response to SEA was high in the CD4+ 45RO+ memory T cell subset, whereas CD4+ 45RA+ naive T cells and CD8+ T cells had lower IL-1-inducing capacity. The T cell help for IL-1 production could not be replaced by a panel of T cell-derived recombinant lymphokines added to SEA-stimulated monocytes, including IFN-gamma and TNF, indicating the participation of cell membrane-bound ligands or hitherto unidentified soluble mediators.     

Contribution of IL-1 beta and TNF-alpha to the initiation of the peripheral lung response to atmospheric particulates (PM10)

Alveolar macrophages (AM) play a key role in clearing atmospheric particulates from the lung surface and stimulating epithelial cells to produce proinflammatory mediators. The present study examines the role of "acute response" cytokines TNF-alpha and IL-1 beta released by AM exposed to ambient particulate matter with a diameter of <10 microm (PM(10)) in amplifying the proinflammatory mediator expression by A549 cells and human bronchial epithelial cells (HBEC). The results showed that supernatants from human AM incubated 24 h with PM(10) (100 microg/ml) contained more TNF-alpha, IL-1 beta, granulocyte-macrophage colony stimulating factor, IL-6, and IL-8 than nonexposed AM supernatants. The 3-h treatment of A549 cells with PM(10)-exposed AM supernatants increased TNF-alpha, IL-1 beta, IL-8, regulated on activation normal T-cells expressed and secreted (RANTES), and leukemia inhibitory factor mRNA compared with the treatment with nonexposed AM supernatants and, compared with untreated A549 cells, additionally increased ICAM-1 and monocyte chemotactic protein-1 mRNA. Preincubating PM(10)-exposed AM supernatants with anti-IL-1 beta antibodies reduced all the above mediators as well as VEGF mRNA expression (P < 0.05), while anti-TNF-alpha antibodies were less effective (P > 0.05), and the combination of the two antibodies most effective. When HBEC were treated similarly, anti-TNF-alpha antibodies had the greatest effect. In A549 cells PM(10)-exposed AM supernatants increased NF-kappa B, activator protein (AP)-1 and specificity protein 1 binding, while anti-TNF-alpha and anti-IL-1 beta antibodies reduced NF-kappa B and AP-1 binding. We conclude that AM-derived TNF-alpha and IL-1 beta provide a major stimulus for the production of proinflammatory mediators by lung epithelial cells and that their relative importance may depend on the type of epithelial cell target.     

Thymic microenvironment induces HIV expression. Physiologic secretion of IL-6 by thymic epithelial cells up-regulates virus expression in chronically infected cells

The hallmark of infection with HIV-1 is progressive depletion and qualitative dysfunction of the CD4+ Th cell population in infected individuals. Clinical trials of antiretroviral agents have shown that, despite suppression of virus replication, regeneration of the T cell pool does not occur. One proposed explanation for the defective regenerative capacity of the CD4+ T cell pool is infection of early T lymphocyte progenitors or stem cells. An additional explanation could be failure of cells of the intrathymic microenvironment (thymic epithelial (TE) cells) to carry out critical nurturing functions for developing thymocytes, i.e., secretion of thymocyte-trophic cytokines and expression of adhesion molecules. This study examines the effect of HIV on cultured TE cells and determines the role of TE cells in the regulation of viral expression in chronically HIV-infected cells. We found no evidence of infection of TE cells after exposure to HIV-1. However, normal human serum induced secretion of IL-6 by TE cells; induction of TE IL-6 was partially blocked by anti-IFN-gamma antibodies. Moreover, supernatants from TE cells maintained in normal human serum up-regulated HIV replication in chronically HIV-1-infected cells. Because intrathymic T cell precursors can be infected with HIV and T cell precursors come into close contact with TE cells in the thymus, IL-6 secreted by TE cells during normal intrathymic development may induce HIV expression in infected thymocytes in vivo and promote the intrathymic spread of HIV.     

Decreased IL-7 Responsiveness Is Related to Oxidative Stress in HIV Disease

HIV disease results in decreased IL-7 receptor expression and IL-7 responsiveness in T cells. To explore mechanisms of these deficiencies, we compared CD127 expression and IL-7 induction of P-STAT5 in T cells from HIV-infected persons with serum concentrations of cytokines (IL-7, IL-6 and IL-15), markers of microbial translocation (sCD14 and LPS), and with an indicator of oxidative stress (malondialdehyde (MDA) adducts). CD127 expression was directly related to IL-7 responsiveness in most CD8+ T cell subsets but not in CD4+ T cells from HIV-infected persons. MDA adducts were increased in serum of HIV-infected patients and were inversely related to IL-7 responsiveness in CD8+ T cells and in central memory CD4+ T cells. Incubation of T cells from healthy controls with hydrogen peroxide resulted in impairments in IL-7 induction of P-STAT5. These findings suggest that oxidative stress that is characteristic of HIV disease could contribute to impairments in IL-7 responsiveness and disrupt T cell homeostasis.     

The Characteristics of Th1/Th2 Cytokine Receptors on Monocytes in Untreated Patients of Long Term Nonprogressor or Chronic HIV Infection

Monocytes/macrophages play crucial roles in immunity to microorganisms and are one of the important targets for human immunodeficiency virus (HIV) infection. The phenotypes and function of monocytes in HIV-infected patients were poorly determined. We herein detected the expression of Th1/Th2 cytokine receptors on monocyte subsets in the untreated HIV-infected patients of either long term nonprogressor (LTNP) or chronic infection (CHI). CD14+CD16- monocytes were significantly increased and CD14+CD16+ monocytes were reduced in patients of LTNP or CHI compared with healthy control. IL-6R expression on CD14+CD16- monocytes were decreased in patients of LTNP or CHI, whereas IL-4R and IL-10R expression on both CD14+CD16- and CD14+CD16+ monocyte subsets were increased in patients with LTNP or CHI, as determined by flow cytometry and real time PCR assays. The decreased IL-6R expression and enhanced IL-4R and IL-10R expression were also observed on CD4+ T cells of these patients, indicating that these changes in monocytes are not cell-specific. CD14+CD16- monocytes of HIV-infected patients produced less TNF-α and IL-1β but identical levels of IL-6, and IL-12 as the control after IFN-γ/LPS stimulation. However, in the presence of IL-4 or IL10, CD14+CD16- monocytes of HIV-infected patients produced more TNF-α, IL-6, IL-12 or Il-1β after IFN-γ/LPS stimulation than the healthy control, supporting the impaired IL-4R and IL-10R signal pathways in patients with LTNP and CHI. Therefore, our present study offered the basic information for the Th1/Th2 cytokine receptor expression and function on monocyte subsets in untreated HIV-infected individuals.     

Differential requirement for accessory cells in polyclonal T-cell activation

Highly purified rat Ia-negative (OX-6-) and Ia-positive (OX-6+) T cells were employed to examine the requirement for accessory cells (AC) and/or soluble factors in the activation of resting T cells with Con A, PHA, sodium periodate, or antigen. A variety of cells were employed as AC, including Ia-positive and Ia-negative macrophages (M phi), gamma-irradiated (2000 rad) or non-irradiated OX-6+ T cells, and several Ia-negative adenovirus-transformed rat embryo fibroblast cell lines. Our results suggested that for the expression of IL-2 receptors (IL-2R) and proliferation of OX-6- T cells in response to Con A, PHA, or antigen, there was an obligatory requirement for the presence of AC which could not be overcome by the addition of IL-1 and/or IL-2. Activation of OX-6- T cells with antigen required the presence of Ia+ AC, while activation with mitogens could be initiated with Ia- AC. M phi were efficient in AC function in all responses tested, while the AC function of OX-6+ T cells (TAPC) proved discriminatory under different conditions. The optimal response to PHA required much higher concentrations of TAPC as AC than for the Con A response. TAPC failed to stimulate sodium periodate-treated T cells under any conditions tested. Furthermore, when TAPC were employed as AC, their antigen-presenting ability was radiosensitive, while their AC function for Con A and PHA was radioresistant. These results suggest that molecules involved in T cell-AC interactions may differ, depending on the source of AC and/or type of the proliferative stimulus provided to T cells. This data has been discussed in the context of T-cell activation.     

Regulation of mucosal B cell immunoglobulin secretion by intestinal epithelial cell-derived cytokines

Intestinal epithelial cells (IEC) secrete a variety of cytokines and, because of their close proximity to B cells in the lamina propria, may affect local antibody production via these cytokines. However, studies have not yet addressed which and to what extent these IEC-derived cytokines may affect B cell antibody production. In this study, rat mesenteric lymph node B cells were cultured with culture supernatants from the rat IEC-6 intestinal epithelial cell line to determine their effect on immunoglobulin (Ig) secretion. Unstimulated IEC-6 cells were found to secrete sufficient levels of IL-6 to enhance IgA, IgG and IgM secretion by unstimulated B cells. However, culture of lipopolysaccharide (LPS)-stimulated B cells with the unstimulated IEC-6 supernatant resulted in an enhancement of IgA secretion while IgM secretion was significantly suppressed. Depletion of the IEC-6 supernatant using cytokine specific antibodies revealed that both interleukin 6 (IL-6) and transforming growth factor beta (TGF-beta) were responsible for the enhanced IgA secretion while TGF-beta suppressed IgM secretion. More importantly, culture supernatants from LPS stimulated IEC-6 cells contained enhanced levels of IL-6 which enhanced both IgG and IgA production and partially overcame the suppressive effect of TGF-beta on IgM secretion. These results suggest that intestinal epithelial cells may secrete IL-6 and TGF-beta to regulate local B cell antibody secretion and their effect may be highly dependent upon the activation state of the epithelial cells.     

Immunostimulatory action of AC II--an ayurvedic formulation useful in HIV

Immunostimulatory activity of AC II, a registered ayurvedic preparation prepared at Amala Ayurvedic Research Centre for treating HIV and AIDS is reported. AC II administration could significantly enhance the mitogen-induced proliferation of lymphocytes of spleen cells. It was also found to increase cell-mediated immune responses in normal and tumor-bearing control animals. Oral administration of AC II significantly enhanced Natural Killer cell activity in normal and tumor-bearing animals on the 7th day, which was observed earlier than the tumor-bearing control animals and normal animals. Antibody dependent cellular cytotoxicity (ADCC) was also increased in AC II treated normal and tumor-bearing animals. An early enhancement of antibody-dependent complement-mediated cytotoxicity was also observed by the administration of AC II in normal as well as tumor-bearing animals. Treatment with AC II elevated the levels of IL-2, TNF-alpha and IFN-gamma in normal mice. Administration of AC II was also found to increase the cytotoxic T lymphocyte production in EL4 treated mice. These studies support the use of this immune stimulatory preparation in HIV patients.     

Impaired TCR-mediated induction of Ki67 by naive CD4+ T cells is only occasionally corrected by exogenous IL-2 in HIV-1 infection

Perturbations in naive T cell homeostasis and function may play a major role in the immunodeficiency that accompanies HIV infection. By examining naive CD4(+) T cell function on a single cell basis, we provide evidence that these cells have significant qualitative defects in HIV disease. Ki67, a molecule expressed during cell cycle progression, is induced less efficiently among naive CD4(+) T cells from HIV-infected individuals following activation with anti-TCR Ab. The impairment in Ki67 expression is evident even when a separate function, CD62L down-modulation, is within normal ranges. Moreover, the defects in Ki67 induction are only sometimes corrected by the addition of rIL-2 to cell cultures. An initial assessment of IL-2 unresponsiveness in cells from selected HIV-infected individuals suggests that the defect is not a consequence of impaired IL-2R expression or IL-2R signaling capability. Qualitative defects in naive T cells that cannot be routinely corrected by IL-2 have significant implications for disease pathogenesis and for strategies using IL-2 as a vaccine adjuvant in HIV disease.     

Growth of single B cell clones is enhanced by products of a T cell line

In this paper we show the presence of a B cell growth-promoting activity in T cell replacing factor (TRF) supernatants from a monoclonal T cell line and polyclonally activated splenic T cells. The target cell of this activity is indisputably shown to be the B cell, which indicates that T cell-derived factors can act directly on B cells. The effect of monoclonal TRF-containing supernatant from the C.C3.11.75 Dennert cell line, (DL)TRF, which demonstrates B cell growth-promoting activity, is to increase the frequency of B cell clones stimulated by mitogens as opposed to increasing B cell clone sizes. (DL)TRF B cell growth enhancement is observed when B cells are activated by fetal calf serum mitogens, lipopolysaccharide (LPS), dextran sulfate (DXS), or LPS + DXS. The growth-promoting activity of (DL)TRF appears to be that of a costimulator rather than a classical growth factor because (DL)TRF alone is not sufficient to maintain clonal growth of activated B lymphoblasts.     

Decreased stimulation of CD4+ T cell proliferation and IL-2 production by highly enriched populations of HIV-infected dendritic cells

APC infection and dysfunction may contribute to the immunopathogenesis of HIV disease. In this study, we examined immunologic function of highly enriched populations of HIV-infected monocyte-derived dendritic cells (DC). Compared with uninfected DC, HIV-infected DC markedly down-regulated surface expression of CD4. HIV p24(+) DC were then enriched by negative selection of CD4(+)HIV p24(-) DC and assessed for cytokine secretion and immunologic function. Although enriched populations of HIV-infected DC secreted increased IL-12p70 and decreased IL-10, these cells were poor stimulators of allogeneic CD4(+) T cell proliferation and IL-2 production. Interestingly, HIV-infected DC secreted HIV gp120 and the addition of soluble (s) CD4 (a known ligand for HIV gp120) to DC-CD4(+) T cell cocultures restored T cell proliferation in a dose-dependent manner. By contrast, addition of antiretroviral drugs did not affect CD4(+) T cell proliferation. Furthermore, recombinant HIV gp120 inhibited proliferation in uninfected cocultures of allogeneic DC and CD4(+) T cells, an effect that was also reversed by addition of sCD4. In summary, we show that HIV gp120 produced by DC infected by HIV in vitro impairs normal CD4(+) T cell function and that sCD4 completely reverses HIV gp120-mediated immunosuppression. We hypothesize that HIV-infected DC may contribute to impaired CD4(+) T cell-mediated immune responses in vivo and that agents that block this particular immunosuppression may be potential immune adjuvants in HIV-infected individuals.     

Complex effects of interferon-alpha on the cytokine network in HIV infection--possible contribution to immunosuppression

Since interleukin (IL-)2, IL-10 and IL-12 may contribute to the pathogenesis of human immune deficiency virus (HIV) infection we examined the effect of interferon (IFN)-alpha on these cytokines in cultures of various subsets of peripheral blood mononuclear cells (PBMC) in ten HIV-infected patients and ten healthy controls. Our main findings were: (1) IFN-alpha markedly enhanced IL-10 levels in a dose-dependent manner in both lipopolysaccharide (LPS)- and phytohaemagglutinin (PHA)-stimulated PBMC, as well as in anti-CD3- and anti-CD3/anti-CD28-stimulated T cells in both HIV-infected patients and controls. (2) In contrast, IFN-alpha had a downregulatory effect on IL-10 levels in Candida -stimulated PBMC,with particularly strong suppressive effect in HIV-infected patients. (3) Furthermore, IFN-alpha had a significant but modest stimulatory effect on IL-2 levels in PHA- and Candida -stimulated PBMC and anti-CD3-stimulated T cells. (4) IFN-alpha enhanced IL-12 levels in a dose-dependent manner in LPS-stimulated PBMC in both patients and controls. Our findings that IFN-alpha markedly enhanced IL-10 and modestly enhanced IL-2 and IL-12, suggest a net immunosuppressive effect of IFN-alpha in HIV-infected patients, possibly contributing to progression of immunodeficiency in these patients.     

HIV infection of placental macrophages: effect on the secretion of HIV stimulatory cytokines.

Vertical transmission of HIV-1 can occur at three different stages: during gestation, delivery and breast feeding. To determine the role of cytokines in vertical transmission of HIV during gestation, we studied the secretion of IL-1beta, TNF-alpha and IL-6 from in vitro infected and Mock-infected placental macrophages (Hofbauer cells) in comparison to blood monocyte derived macrophages (MDM). Hofbauer cells stimulated with lipopolysaccharide (LPS) secreted lower levels of HIV stimulatory cytokines (6-8 ng/ml) in the supernatants than MDM (26 ng/ml, p<0.005). Cytokine levels in MDM decreased upon HIV infection to 7 ng/ml. IL-6 was the major cytokine produced after LPS stimulation by the two cell populations (p<0.005), being MDM the major cytokine producer. In vitro infection studies with a M-tropic virus (HIV-BaL) indicated that MDM were 10x more susceptible to HIV than placental macrophages (p=0.001). Our results indicate that although macrophages from term placenta secrete lower amount of HIV stimulatory cytokines than MDM, there was no correlation between the levels of cytokines and HIV production by both cells.     

Functional gamma delta T-lymphocyte defect associated with human immunodeficiency virus infections.

BACKGROUND: Antiviral cellular immune responses may influence immunological homeostasis in HIV-infected persons. Recent data indicate that V gamma 9/V delta 2 T lymphocytes display potent cytotoxic activities against human cells infected with certain viruses including HIV. Understanding the role of gamma delta T cells in the course of HIV infection may be helpful for designing novel treatment strategies for HIV-associated disorders. MATERIALS AND METHODS: The constitutive recognition of Daudi cells and monoethyl pyrophosphate (Etpp) by peripheral blood V gamma 9/V delta 2 T cells was assessed using a proliferation assay. The cytotoxicity of Daudi-stimulated lymphocyte populations was measured by chromium release assays. The HIV infectivity for gamma delta T cell clones was determined by measuring the levels of HIV p24 in cell supernatants. The effect of in vitro HIV-infection on cytokine mRNA production by gamma delta T cell clones was assessed by PCR. RESULTS: The constitutive proliferative responses of peripheral blood V gamma 9/V delta 2 T cells and the lytic functions of Daudi-expanded lymphoid cells from HIV+ persons were substantially diminished in comparison with those of HIV-seronegative persons. These alterations were present in asymptomatic HIV+ persons prior to substantial alpha beta CD4+ T cell loss. Productive HIV infection of gamma delta T cells in vitro had no measurable effect either on their proliferative response to Daudi stimuli or on the expression of cytokine mRNAs for IFN-gamma, IL-2, IL-4, IL-5, IL-6, IL-10, and IL-13. CONCLUSIONS: The constitutive responsiveness of V gamma 9/V delta 2 T lymphocytes to Daudi and Etpp is severely altered in HIV+ persons. HIV infection of gamma delta T cells in vitro does not substantially change their cytokine expression or antigenic response.     

IL-6 production by human T lymphocytes. Expression in HTLV-1-infected but not in normal T cells

IL-6 is an important regulator of humoral and cellular immunity. Although this cytokine is produced by diverse cell types, it is not known whether it is produced by T lymphocytes under physiologic conditions or which agents can induce T cell expression of IL-6. We analyzed the production of IL-6 by human peripheral blood T cells, human thymocytes, and human T cell lines. In pure populations of these cells, stimulated with different combinations of various mitogens and cytokines, IL-6 activity could not be detected. Analysis of purified T-alpha beta and T-gamma delta cells showed that neither T cell subset produced IL-6. Similarly, IL-6 mRNA was not detected in T cell or thymocyte populations for up to 48 h after stimulation. With the use of a PCR assay, IL-6 mRNA in T cells was found to be virtually negligible, and did not change after T cell activation. By in situ hybridization it was shown that the cells expressing IL-6 mRNA after mitogen activation of PBMC do not belong to the T cell lineage. To analyze whether human T cells express IL-6 in vivo, we examined lymphoid tissues by in situ hybridization. In normal human thymus there was no detectable signal for IL-6. Tonsils showed only few positive cells within the parenchyma, but strong expression of IL-6 by epithelial cells in crypts. In contrast to normal lymph node, which contained only rare cells positive for IL-6, a lymph node from a patient with Castleman's disease showed IL-6 expression in cells occupying the marginal sinus and interfollicular areas. Screening of various human T cell lines showed that all cell lines infected with HTLV-1 secrete IL-6 activity and express IL-6 mRNA. In addition, in vitro infection of peripheral blood T cells with HTLV-1 induced de novo synthesis and secretion of IL-6. Furthermore, IL-6 expression in HTLV-1-infected cells was enhanced by stimulation with IL-1 beta or TNF-alpha. In contrast, IL-6 was not detectable in non-infected T cell lines. These studies indicate that IL-6 may not be a physiologic product of human T lymphocytes and that infection of T cells with HTLV-1 results in aberrant expression of this cytokine.     

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.