Splenic and inguinal lymph node T cells of aged mice respond differently to polyclonal and antigen-specific stimuli.

Numerous changes have been reported to occur in T cell responsiveness of mice with increasing age. However, most of these studies have examined polyclonal stimulation of spleen cells from a limited number of mouse strains. This study investigated the influence of genetic background, source of lymphocytes, and type of stimulus on age-associated changes in T cells response. Con A-induced proliferation and IL-2 and IFN-gamma production by splenic lymphocytes (SL) was significantly greater in CBA/Ca mice compared to C57BL/6 mice, regardless of age. SL of both strains exhibited the predicted age-dependent decline in proliferative response and an increase in IFN-gamma production in response to Con A. In contrast, however, only SL from C57BL/6 mice demonstrated the predicted age-dependent decline in Con A-induced IL-2 production; Con A-induced SL of young and aged CBA/Ca mice produced comparable amounts of IL-2. Differences in age-associated responses to Con A were also observed between SL and inguinal lymph node (ILN) cells of CBA/Ca mice. In contrast to SL, ILN cells demonstrated an increased proliferative response to Con A. However, lymphokine production by Con A-stimulated ILN cells from aged CBA/Ca mice was similar to that of Con A-stimulated SL from aged CBA/Ca mice. To determine if aged ILN T cells respond similarly to polyclonal and antigen-specific stimuli, keyhole limpet hemocyanin (KLH) responses of T cells isolated from ILN of aged and young CBA/Ca mice were examined. KLH-specific T cells from aged mice cultured with KLH-pulsed macrophages (M phi) from aged mice were significantly reduced in their ability to proliferate compared to KLH-specific T cells of young mice cultured with young KLH-pulsed M phi. In contrast to the expected results, the defect was not at the level of the T cells; proliferation of young T cells cultured with aged KLH-pulsed M phi was equivalent to the proliferation of aged T cells cultured with aged M phi. These results suggest that aging has differential effects on polyclonal and antigen-specific T cell proliferation and on polyclonal stimulation of T cells isolated from different lymphoid organs and from different strains of mice.     

Enhancement of antigen-presenting function of dendritic cells with culture supernatants of mouse peritoneal macrophages stimulated with certain particulate substances

The production from murine resident peritoneal macrophages (M phi) of a soluble factor, which was capable of enhancing the antigen-presenting (AP) function of dendritic cells (DC), was examined. The supernatants of peritoneal M phi (M phi sup) were prepared by culturing peritoneal M phi with particles, i.e., zymosan A, latex, and sheep red blood cells (SRBC), or antigen-antibody (Ag-Ab) complexes such as keyhole limpet hemocyanin (KLH)-anti-KLH, ovalbumin (OVA)-anti-OVA, and SRBC-anti-SRBC complexes. When exposed to M phi sup during antigen pulsing DC induced a marked antigen-specific T cell proliferation, relative to DC treated with the supernatants from M phi cultured without stimuli (control sup). On the other hand, M phi sup-treated splenic M phi stimulated antigen-specific T cell activation to almost the same extent as did splenic M phi treated with control sup. These results indicated that peritoneal M phi elaborated a soluble factor which preferentially enhanced the AP capacity of DC when stimulated with particles or Ag-Ab complexes. Analytical gel filtration of M phi sup revealed that the factor had an apparent molecular weight of 27,000 daltons which was distinct from interleukin 1.     

Inhibition of macrophage-induced antigen-specific T lymphocyte proliferation by poly I:C: strain and antigen independence

We have previously demonstrated that IFN-alpha/beta, poly I:C (an inducer of IFN-alpha/beta), and IFN-gamma can inhibit the ability of KLH-pulsed peritoneal macrophages to induce proliferation of syngeneic, KLH immune T lymphocytes in CBA/J mice. In this study, we show that this IFN-induced immunosuppression is not restricted to CBA/J (H-2k) mice but is also seen in BALB/cJ (H-2d) mice. A similar inhibition of proliferation is observed with the KLH-specific T cell hybridoma BDK, 100, which requires KLH-pulsed macrophages for optimum proliferation and IL-2 production. The immunosuppression produced by IFN was also independent of the antigen employed. Inhibition of T lymphocyte proliferation was observed when casein, instead of KLH, was used to immunize T cells and to pulse peritoneal macrophages in vivo. Utilizing KLH and casein, the antigen specificity of the inhibition was demonstrated. Therefore, the inhibition by the IFN-inducer poly I:C of macrophage-induced, antigen-specific T cell proliferation is not limited by H-2 type of the mice or to one antigen.     

Modulation of Ia-like antigen expression and antigen-presenting activity of human monocytes by endotoxin and zymosan A

The environmental agents E. coli endotoxin and zymosan A modulated antigen-specific T cell proliferation in vitro, assessed by 3H-TdR uptake. In the continual presence of these agents, human mononuclear leukocyte responses to the antigens tuberculin PPD, Candida albicans, and mumps were significantly reduced. Treatment of adherent cell-depleted T cells with the agents did not affect their subsequent reactivity to soluble antigens in the presence of normal M phi. However, cultures consisting of pretreated M phi, normal T cells, and soluble antigen gave responses that were only 7 to 38% of control values, indicating that the function of the antigen-presenting cell, not the T cell, was inhibited. This effect was observed only when treatment with endotoxin or zymosan A preceded antigen stimulation by at least 24 hr, suggesting that a gradual inhibition of antigen presentation had occurred. When various ratios of normal antigen-pulsed and agent-treated M phi were cultured with normal T cells, antigen-specific responses were not significantly different from control cultures; this indicated that M phi-mediated suppression was not involved. It did not appear that the inhibition was due to enhanced antigen degradation by the treated M phi because responses were not reconstituted in the presence of excess antigen. After endotoxin or zymosan A treatment of the M phi population the proportion of Ia+ cells was reduced significantly, and surface expression of Ia antigen correlated with the ability of the cell population to present antigens to immune T cells. This suggested that endotoxin and zymosan A induce a loss of surface Ia antigen on antigen-presenting cells that inhibits immune T cell activation.     

Role of macrophages as modulators but not as autonomous accessory cells in the proliferative response of immune T cells to soluble antigen

The role of murine macrophages (M phi) and that of splenic dendritic cells (DC) were investigated in the antigen-specific proliferative response of memory T cells of mice primed with key-hole limpet hemocyanin (KLH) 6 weeks or more before. Peritoneal M phi, whether expressing Ia antigens or not, did not function as autonomous accessory cells (A cells). A-cell activity of the spleen adherent cell population, which comprised M phi in the majority and DC in the minority, was abolished by eliminating DC with a DC-specific monoclonal antibody and complement, and regained by the addition of a small number of DC. Though M phi did not function as autonomous A cells, they augmented the proliferative response in the presence of a small number of DC. This occurred not only in the presence of free antigen, but also when DC and/or M phi were pulsed with antigen. A culture supernatant of M phi having interleukin-1 activity was effective in enhancing the proliferation of T cells which responded to antigen-pulsed DC. On the other hand, interleukin-2 did not replace DC even in the presence of antigen-pulsed Ia+ M phi. We also investigated recently primed T cells, but no evidence was obtained in favor of the competence of M phi as autonomous A cells.     

The capacity of murine alveolar macrophages to stimulate antigen-dependent T-lymphocyte activation and proliferation

To define the antigen-presenting capacity of alveolar macrophages (AM phi), their ability to activate antigen-specific T cells was determined. It was found that AM phi s are at least as potent as spleen cells at presenting alloantigen or soluble protein antigen plus I-region determinant to cloned T-cell hybridomas. Activation of those hybridomas, shown by interleukin 2 (IL-2) secretion, further indicated the presence on AM phi s of functional products of the I-A and I-E subregions. In addition, it was found that AM phi s are at least as potent as spleen cells and peritoneal macrophages at inducing, in a restricted fashion, specific proliferation of primed, propagated lymph node T cells. AM phi s are thus potent accessory cells in vitro, whose in vivo significance in this capacity remains to be defined.     

Activation of T Cells by Autoantigen Immobilized by Specific Antibodies

A convenient microtiter-plate assay that uses immobilized antibody to capture specific antigens for presentation to T cells has been developed. Initial experiments used KLH as the antigen, immune antisera and draining lymph node cells from immunized NOD mice as the source of antibody and T cells, and spleen cells from naive NOD mice as the source of antigen-presenting cells (APCs). The resulting proliferation of the T cells was shown to be antibody- and antigen-specific, suggesting that the APCs had internalized and processed the captured antigen, presenting it to the T cells in the form of peptide/MHC complexes. The approach was also tested for an autoimmune disease as part of an effort to identify autoantigens responsible for the proliferation of T cells in the synovial fluid of rheumatoid arthritis patients. When immunoglobulin from autologous synovial fluid was captured on plates coated with anti-human immunoglobulin antibodies, the addition of HLA-DR4 peripheral blood mononuclear cells as APCs and synovial fluid-reactive HLA-DR4-restricted T-cell clones resulted in significant proliferation, indicating that the specific antigen in the crude synovial fluid was human immunoglobulin. This response was also shown to be antigen-specific and HLA-DR4-restricted. This assay format should permit the definition of autoantigens by capturing with antibodies to crude autoantigen extracts, followed by the addition of the appropriate APC and T-cell populations.     

Tumor modulation of autoreactivity: decreased macrophage and autoreactive T cell interactions

The autologous mixed lymphocyte reaction (AMLR) is an in vitro measure of autoreactivity, a key mechanism in immune homeostasis. In this system, macrophages (M phi) act as accessory cells to autoreactive L3T4+ T cells by presenting self-Ia and releasing soluble modulators. During tumor growth, changes occur in M phi and T cells. Tumor-bearing host (TBH) M phi have a reduced ability to act as accessory cells. In fact, TBH M phi suppressed autoreactivity by 60-70%. The decrease in TBH M phi or T-cell abilities was not due to differences in cell numbers or incubation time. Because tumor growth causes increased prostaglandin E2 (PGE2) production by M phi, indomethacin was used to assess the contribution of prostaglandins. Normal and TBH T-cell reactivity increased nearly 50% when stimulated by normal host M phi, while normal and TBH T-cell reactivity increased nearly 100% when stimulated by TBH M phi. Thus increased prostaglandin production is partly responsible for the increased TBH suppressor M phi activity and in the normal host, suppressor M phi may be responsible for maintaining immune regulation. To assess the direct role of prostaglandins in T-cell hyporesponsiveness, PGE2 was titrated into the cultures. PGE2 suppressed normal and TBH T-cell responsiveness in a dose-dependent manner. Normal host T cells were suppressed to a greater extent than TBH T cells by PGE2 (66% versus 42% suppression, respectively). Reduced Ia expression and active suppressor mechanisms are not the only mechanisms mediating hypoautoreactivity during tumor growth. TBH autoreactive L3T4+ T cells were less responsive to self-Ia; they were only 60-80% as reactive as their normal counterparts. To address whether the helper T (TH)-cell defect involved cytokines, T cells were treated with interleukin (IL)-1, IL-2, and IL-4. In all cases, the TBH T-cell response to the factors was decreased (only 60-75% as reactive as normal T cells). Because TBH M phi-mediated suppression can override the addition of IL-1, IL-2, and IL-4, indomethacin was also added with the exogenous interleukins. This coaddition significantly enhanced normal host autoreactivity above control levels while TBH autoreactivity (the combination of TBH T cells and TBH M phi) only returned to normal host unstimulated levels. Tumor growth modulates the immune response at least by (i) decreasing the accessory cell abilities of TBH M phi through decreased Ia expression and increased production of suppressive molecules such as prostaglandins; and (ii) decreasing the responsiveness to immune enhancing factors by TH cells.     

Clonal analysis of antigen-specific interactions between T cells and genetically engineered B cells

In order to investigate T cell-B cell interactions we constructed monoclonal, antigen-specific T- and B-cell populations. The Ia+ B-cell lymphoma A20-2J was transfected with trinitrophenyl (TNP)-specific heavy (mu) and light (kappa) chain Ig genes. A hapten-carrier complex (TNP-keyhole limpet hemocyanin (KLH)) bound to the surface Ig expressed on the transfectant and was presented to carrier-specific T-cell hybridoma clones at markedly low doses of antigen (0.01 microgram/ml) and in an Ia-restricted fashion. Two responses were elicited in the responding T-cell clones: (i) high levels of IL-2 secretion (320 units/ml), and (ii) cytotoxicity directed against the antigen-presenting B cell. This cytotoxicity was inhibited by D-mannose and was directed against innocent bystander cells, unlike cytotoxicity mediated by NK cells or alloreactive cytotoxic T lymphocyte. Helper and cytotoxic functions were often present in different T-cell hybridomas but some clones exhibited both activities. One representative T-cell hybridoma exhibited strong helper function for TNP-primed splenic B cells as detected in a plaque-forming cell assay, but was cytotoxic toward antigen-presenting B cells. Such monoclonal assay systems for studying cognate interactions of heterogeneous T cells and specific antigen-presenting cells will provide us with valuable new approaches for the study of antigen-specific T-cell regulation of B-cell activation in immune responses.     

结核杆菌感染T细胞介导免疫应答研究的新进展

结核病对免疫学家构成了巨大的挑战,因为它是一种慢性传染性疾病,病原体具有持久性特点.在对人和动物进行实验时,检测到结核分枝杆菌适应性免疫应答的特点之一为感染早期T细胞免疫应答延迟.新近研究揭示了此种延迟应答的机制:通过结核杆菌抑制免疫细胞(CD4+和CD8+T细胞及DC)凋亡延迟应答,通过特异性Treg细胞抑制作用延迟应答.结核杆菌慢性感染期间存在IFNγ信号调节网络和ESAT-6抗原的慢性刺激作用,抗原特异性PD-1+ CD4+T细胞具有高度增殖分化为更多终末效应性T细胞的潜能,以此可调节和维持免疫应答.深入了解抗原特异性T细胞调节与维持适应性免疫应答的机制,有益于抗结核疫苗的设计和研制.     

Regulatory T cells secreting IL-10 dominate the immune response to EBV latent membrane protein 1

Viruses exploit a number of strategies to evade immune recognition. In this study, we describe a novel mechanism by which EBV, rather than avoiding detection, subverts the immune response by stimulating regulatory T cells that secrete IL-10. Human PBMC from all EBV-seropositive, but not -seronegative, donors responded to both purified latent membrane protein 1 and the corresponding immunodominant peptides with high levels of IL-10 secretion by CD4(+) T cells. These IL-10 responses, characteristic of T regulatory 1 cells, inhibited T cell proliferation and IFN-gamma secretion induced by both mitogen and recall Ag. It was confirmed that the inhibition was IL-10 dependent by the use of neutralizing Ab. The deviation of the immune response toward suppression is likely to be important in maintaining latency and EBV-associated tumors.     

A comparison of the stimulatory activities of lymphoid dendritic cells and macrophages in T proliferative responses to various antigens

The identities of murine accessory cells and the mechanism by which they process antigen and stimulate T cell proliferation have been examined with cell separation techniques and specific agents to block antigen catabolism. Using preparations of splenic dendritic cells (DC) and macrophages (M phi) with minimal cross-contamination, we found that only DC could induce syngeneic mixed leukocyte reaction (MLR), whereas both DC and M phi could initiate allogeneic MLR. This observation may have significant implications for syngeneic MLR as a manifestation of self Ia recognition, and for the cell type that defines self Ia during ontogeny. DC and M phi could present soluble antigens such as purified protein derivative of tuberculin (PPD) and Salmonella flagellin about equally well to antigen-specific T cell lines. M phi, however, were much more effective than the non-phagocytic DC at inducing T cell proliferation to whole Corynebacterium parvum organisms. These differences could not be attributed to differences in antigen uptake. The results suggest that the bacteria must be ingested and processed by phagocytes before T cell activation. Using the lysosomotropic agent chloroquine to inhibit antigen catabolism in accessory cells, we found that the presentation of large antigens by M phi and DC was abolished by chloroquine treatment, whereas T cell activation by antigens (such as PPD or integral membrane Ia for MLR) that apparently required no processing was relatively insensitive to chloroquine. Thus, in addition to differences between cells, discrete functions within each cell type can also be distinguished.     

Interferon-mediated protection of B16 melanoma cells from cytotoxicity by activated macrophages

Corynebacterium parvum-activated macrophages (M phi), purified by adherence, were cytotoxic for B16 melanoma cells maintained in vitro. Pretreatment of the melanoma cells for 18 hr with interferon-alpha/beta or -gamma (IFN-alpha/beta or -gamma) caused a reduced susceptibility of the B16 cells to M phi-mediated cytotoxicity. The IFN-induced protective effect of B16 cells from cytotoxic M phi was found to be dose dependent. In addition, IFN-gamma was more protective than IFN-alpha/beta. The protective effect observed with partially purified IFN was reproduced by using highly purified IFN-alpha/beta or recombinant IFN-gamma. Monoclonal antibodies to IFN-gamma neutralized the protective effect provided by IFN-gamma. These results show that the susceptibility of a tumor cell line to killing by activated M phi can be altered by IFN pretreatment.     

IgM induction in murine B hybridomas with Ia-restricted T cell clones: a monoclonal model for T and B cell interactions in antibody response

The mechanism of MHC-restricted T and B cell interactions in antibody response was studied with IgM-inducible B hybridomas and antigen-specific helper T cell clones. B hybridomas were prepared by fusion between splenic B cells from (CBA/N (H-2k) X BALB/c (H-2d)) F1 (NBF1) male mice and a B lymphoma cell line, M12.4.5. A B hybridoma clone, 1M70, which expressed I-Ad but not I-Ak determinants was chosen in the present study. IgM secretion was induced in 1M70 when it was cocultured with a "resting" KLH-specific and H-2d restricted helper T cell clone in the presence of KLH. A "resting" KLH-specific and H-2k restricted T cell clone did not induce IgM secretion in 1M70 even in the presence of KLH. However, when these KLH-specific T cell clones were activated by KLH and appropriate antigen presenting cells, both H-2d and H-2k restricted T cell clones induced IgM secretion in 1M70 even in the absence of KLH. A monoclonal anti-I-Ad antibody inhibited IgM secretion induced by a "resting" H-2d restricted T cell clone, but not by an "activated" T cell clone. These results indicated that T cell clones recognized antigens in the context of Ia molecules on B hybridomas in a MHC-restricted manner and were activated to produce B cell stimulatory factors which in turn acted on B hybridomas in a non-MHC-restricted manner and induced differentiation of B hybridomas into IgM secreting cells.     

Recombinant modified vaccinia virus Ankara expressing antigen 85A boosts BCG-primed and naturally acquired antimycobacterial immunity in humans

Protective immunity against Mycobacterium tuberculosis depends on the generation of a T(H)1-type cellular immune response, characterized by the secretion of interferon-gamma (IFN-gamma) from antigen-specific T cells. The induction of potent cellular immune responses by vaccination in humans has proven difficult. Recombinant viral vectors, especially poxviruses and adenoviruses, are particularly effective at boosting previously primed CD4(+) and CD8(+) T-cell responses against a number of intracellular pathogens in animal studies. In the first phase 1 study of any candidate subunit vaccine against tuberculosis, recombinant modified vaccinia virus Ankara (MVA) expressing antigen 85A (MVA85A) was found to induce high levels of antigen-specific IFN-gamma-secreting T cells when used alone in bacille Calmette-Guerin (BCG)-naive healthy volunteers. In volunteers who had been vaccinated 0.5-38 years previously with BCG, substantially higher levels of antigen-specific IFN-gamma-secreting T cells were induced, and at 24 weeks after vaccination these levels were 5-30 times greater than in vaccinees administered a single BCG vaccination. Boosting vaccinations with MVA85A could offer a practical and efficient strategy for enhancing and prolonging antimycobacterial immunity in tuberculosis-endemic areas.     

Development and characterization of interleukin-2-independent antigen-specific human T cell clones that produce multiple lymphokines

The development of antigen-specific T lymphocyte lines and clones has greatly facilitated the investigation of T-cell recognition of and response to foreign antigens. In the present study, human antigen-specific helper T cell lines and clones which are completely independent of exogenous interleukin-2 (IL-2) have been developed by cyclic restimulation with the soluble antigen keyhole limpet hemocyanin (KLH) to which the T cell donor had previously been immunized. These T cells uniformly bear the OKT4 phenotype and were shown to require both histocompatible antigen-presenting cells (APC) and antigen for optimal proliferation. The T cell line was composed of a highly antigen-specific and clonable T cell population. Following four cycles of antigen stimulation, limiting dilution cloning analysis showed a Poisson distribution of clonable T cells with a precursor frequency of 0.62, and from 88 to 92% of viable clones were specific for the stimulating antigen. Individual clones were obtained which recognized KLH with either DR 1 (one parental Ia haplotype of the donor) or DR 2 (the other parental Ia haplotype) allogeneic APC, but not both. Following stimulation with KLH, the T cell clones produced IL-2. Peak amounts of IL-2 were assayable in the first 6 to 24 hr after stimulation. In contrast, virtually no IL-2 was detectable in supernatants at 72 to 96 hr, suggesting autoutilization by the proliferating T cells. In addition, some clones were also capable of producing both B cell growth factor and IL-2 following KLH stimulation. These IL-2-independent T cells appeared to be derived from a discrete Leu 8-negative subclass of T4⁺ cells and expressed the full complement of Ia antigen of the donor. Thus, soluble antigen-specific human helper T cell clones have been produced which can be maintained in the absence of exogenous IL-2, elaborate their own growth factors and other immunoregulatory lymphokines, and show fine DR-related restriction to either one or the other parental DR haplotypes in antigen-stimulated proliferative responses.     

Tumor-derived macrophage migration inhibitory factor (MIF) inhibits T lymphocyte activation

Macrophage migration inhibitory factor (MIF) is a multi-functional cytokine that is considered a pro-inflammatory cytokine. However, our studies show that MIF, when produced in super-physiological levels by a murine neuroblastoma cell line (Neuro-2a) exceeding those normally seen during an immune response, inhibits cytokine-, CD3-, and allo-induced T-cell activation. MIF is also able to inhibit T cells that have already received an activation signal. The T-cell inhibitory effects of culture supernatants from neuroblastoma cells were reversed when the cells were transfected with dicer-generated si-RNA to MIF. When T cells were activated in vitro by co-culture with interleukin (IL)-2 and IL-15 and analyzed for cytokine production in the presence or absence of MIF-containing culture supernatant, inhibition of T-cell proliferation and induced cell death were observed even as the treated T cells produced high levels of interferon-gamma (IFN-gamma). The inhibitory effects of MIF were partially reversed when lymphocytes from IFN-gamma knockout mice were tested. We propose that the high levels of MIF produced by neuroblastoma cause activation induced T-cell death through an IFN-gamma pathway and may eliminate activated T cells from the tumor microenvironment and thus contribute to escape from immune surveillance.     

Signals involved in T cell activation. I. Phorbol esters enhance responsiveness but cannot replace intact accessory cells in the induction of mitogen-stimulated T cell proliferation

The role of accessory cells (AC) in the initiation of mitogen-induced T cell proliferation was examined by comparing the effect of intact macrophages (M phi) with that of 4-beta-phorbol 12-myristate 13-acetate (PMA). In high-density cultures, purified guinea pig T cells failed to proliferate in response to stimulation with phytohemagglutinin (PHA), concanavalin A (Con A), or PMA alone. The addition of M phi to PHA or Con A but not PMA-stimulated cultures restored T cell proliferation. The addition of PMA to high-density T cell cultures stimulated with PHA or Con A also permitted [3H]thymidine incorporation, but was less effective than intact M phi in this regard. This action of PMA was dependent on the small number of AC contaminating the T cell cultures as evidenced by the finding that PMA could not support mitogen responsiveness of T cells that had been depleted of Ia-bearing cells by planning, even when these cells were cultured at high density. When PMA was added to T cell cultures supported by optimal numbers of M phi, catalase-reversible suppression of responses was noted. Even in cultures containing catalase, PMA failed to enhance responsiveness above that supported by optimal numbers of M phi. A low-density culture system was used to examine in greater detail the possibility that PMA could completely substitute for M phi in promoting T cells activation. In low-density cultures, mitogen-induced T cell proliferation required intact M phi. PMA could not support responses even in cultures supplemented with interleukin 1-containing M phi supernatants or purified interleukin 2 alone or in combination. Similar results were found in high-density cultures of T cells depleted of Ia-bearing cells. These results support a model of T cell activation in which AC play at least two distinct roles. The initiation of the response requires a signal conveyed by an intact M phi, which cannot be provided by either a M phi supernatant factor or PMA. The response can be amplified by additional M phi or M phi supernatant factors. PMA can substitute for M phi in this regard and can provide the signal necessary for amplification of T cell proliferation supported by small numbers of intact AC.     

Interferon-gamma reduces macrophage-suppressive activity by inhibiting prostaglandin E2 release and inducing interleukin 1 production

Normal peritoneal M phi of C3H/HeN mice were able to suppress lymphocyte proliferation in a dose-dependent fashion when added to Con A-pulsed spleen cell cultures. However, M phi-suppressive activity could be partially or completely reduced by in vitro pre-exposure to nonimmune IFN-alpha or immune recombinant IFN-gamma. For both IFN-alpha and IFN-gamma, reduction of M phi suppression was marginal at 10(1) U/ml and became highly significant at 10(2) to 10(3)/ml. The ability of IFN-alpha and IFN-gamma to modulate M phi suppression appears to be related to distinct mechanisms. In fact, impairment of M phi suppression by IFN-alpha occurred in parallel to the decrease of M phi capacity to produce PGE2 and the oxygen intermediate O2-, two molecules responsible for M phi-suppressive activity. In contrast, M phi exposed to IFN-gamma showed only impairment of PGE2 production, whereas O2- release was not significantly affected. Furthermore, at variance with IFN-alpha, IFN-gamma directly stimulated M phi to synthesize and release IL 1, a monokine known to promote lymphocyte proliferation.     

Tumor cell lysate-pulsed dendritic cells are more effective than TCR Id protein vaccines for active immunotherapy of T cell lymphoma

TCR Id protein conjugated to keyhole limpet hemocyanin (KLH) (TCR Id:KLH) and injected with a chemical adjuvant (QS-21) induces a protective, Id-specific immune response against the murine T cell lymphoma, C6VL. However, Id-based immunotherapy of C6VL has not demonstrated therapeutic efficacy in tumor-bearing mice. We report here that C6VL lysate-pulsed dendritic cells (C6VL-DC) vaccines display enhanced efficacy in both the prevention and the therapy of T cell lymphoma compared with TCR Id:KLH with QS-21 vaccines. C6VL-DC vaccines stimulated potent tumor-specific immunity that protected mice against lethal challenge with C6VL and significantly enhanced the survival of tumor-bearing mice. Tumor-specific proliferation and secretion of IFN-gamma indicative of a Th1-type immune response were observed upon ex vivo stimulation of vaccine-primed lymph node cells. Adoptive transfer of immune T cell-enriched lymphocytes was sufficient to protect naive recipients from lethal tumor challenge. Furthermore, CD8(+) T cells were absolutely required for tumor protection. Although C6VL-DC and control vaccines stimulated low levels of tumor-specific Ab production in mice, Ab levels did not correlate with the protective ability of the vaccine. Thus, tumor cell lysate-pulsed DC vaccines appear to be an effective approach to generate potent T cell-mediated immune responses against T cell malignancies without requiring identification of tumor-specific Ags or patient-specific Id protein expression.