Human glioma-induced immunosuppression involves soluble factor(s) that alters monocyte cytokine profile and surface markers.
Patients with gliomas exhibit deficient in vitro and in vivo T cell immune activity, and human glioblastoma culture supernatants (GCS) inhibit in vitro T lymphocyte responses. Because APC are essential for initiating and regulating T cell responses, we investigated whether GCS would affect cytokines produced by monocytes and T cells from healthy donors of PBMC. Incubation of PBMC with GCS decreased production of IL-12, IFN-gamma, and TNF-alpha, and increased production of IL-6 and IL-10. The GCS-induced changes in IL-12 and IL-10 occurred in monocytes, and involved changes in IL-12 p40 and IL-10 mRNA expression. Incubation with GCS also resulted in reduced expression of MHC class II and of CD80/86 costimulatory molecules on monocytes. The immunosuppressive effects were not the result of IL-6 or TGF-beta1 that was detected in GCS. However, it was due to a factor(s) that is resistant to pH extremes, differentially susceptible to temperature, susceptible to trypsin, and has a minimum molecular mass of 40 kDa. Our findings show that glioblastoma-generated factors that are known to suppress T cell responses alter the cytokine profiles of monocytic APC that, in turn, inhibit T cell function. This model indicates that monocytes can serve as an intermediate between tumor-generated immune-suppressive factors and the T cell responses that are suppressed in gliomas. (+info)
Attachment ligands of viable Toxoplasma gondii induce soluble immunosuppressive factors in human monocytes.
Previous studies have demonstrated that surface antigen proteins, in particular SAG-1, of Toxoplasma gondii are important to this parasite as attachment ligands for the host cell. An in vitro assay was developed to test whether these ligands and other secretory proteins are involved in the immune response of human cells to toxoplasma. Human monocytes were infected with tachyzoites in the presence of antiparasite antibodies, and their effect on mitogen-induced lymphoproliferation was examined. The presence of antibody to either parasite-excreted proteins (MIC-1 and MIC-2) or surface proteins (SAG-1 and SAG-2) during infection neutralized the marked decrease seen in mitogen-induced lymphoproliferation in the presence of infected monocytes. Conversely, antibodies to other secreted proteins (ROP-1) and cytoplasmic molecules had no effect on parasite-induced, monocyte-mediated downregulation. Fluorescence microscope analysis detected microneme and surface antigen proteins on the monocyte cell surface during infection. These results suggest that microneme and surface antigen proteins trigger monocytes to downregulate mitogen-induced lymphoproliferation. (+info)
Suppression of feline immunodeficiency virus replication in vitro by a soluble factor secreted by CD8+ T lymphocytes.
Mitogen-activated lymphoblasts isolated from the blood and lymph nodes, but not the spleen, of domestic cats acutely infected with the Petaluma or Glasgow8 isolates of feline immunodeficiency virus (FIV), suppressed the replication of FIV in the MYA-1 T-cell line in a dose-dependent manner. This effect was not limited to the homologous isolate of FIV. The suppressor activity declined with progression to chronic infection, with lower levels of activity detectable only in the lymph nodes. Immunization of domestic cats with whole inactivated FIV vaccine elicited profound suppressor activity in both the blood and lymph nodes. The suppressor activity was associated with the CD8+ T-cell subpopulation, the effect did not appear to be major histocompatibility complex-restricted, and was mediated by a soluble factor(s). This activity may be associated with the control of virus replication during both the asymptomatic stages of FIV infection, and in the protective immunity observed in cats immunized with whole inactivated virus vaccines. (+info)
Biochemical analysis of the receptor for ubiquitin-like polypeptide.
Monoclonal nonspecific suppressor factor (MNSF), a lymphokine produced by murine T cell hybridoma, possesses pleiotrophic antigen-nonspecific suppressive functions. A cDNA clone encoding MNSF-beta, an isoform of the MNSF, has been isolated and characterized. MNSF-beta cDNA encodes a fusion protein consisting of a ubiquitin-like segment (Ubi-L) and ribosomal protein S30. Ubi-L appears to be cleaved from the ribosomal protein and released extracellularly in association with T cell receptor-like polypeptide. In the current study we have characterized the biochemical nature of the Ubi-L receptor on D.10 G4.1, a murine T helper clone type 2. Biotinylated Ubi-L bound preferentially to concanavalin A-stimulated but not to unstimulated D.10 cells. Detergent-extracted membrane proteins were applied to an immobilized Ubi-L column. SDS-polyacrylamide gel electrophoresis of eluted fraction revealed a band of Mr = 82,000. Biotinylated Ubi-L specifically recognized this band, confirming that the 82-kDa protein is the Ubi-L receptor. A complex of Mr = 90,000 was visualized by immunoprecipitation of 125I-Ubi-L cross-linked to the purified receptor followed by SDS-polyacrylamide gel electrophoresis and autoradiography. In addition, a 105-kDa protein was coimmunoprecipitated by anti-Ubi-L receptor (82-kDa polypeptide) antibody, indicative of the association of this protein with the Ubi-L receptor complex. Amino acid sequence analysis of the 82-kDa polypeptide revealed that the Ubi-L receptor may be a member of a cytokine receptor family. (+info)
Target cells for an immunosuppressive cytokine, glycosylation-inhibiting factor.
Receptors for bioactive glycosylation-inhibiting factor (GIF) were demonstrated using a bioactive mutant of recombinant human (rh) GIF, which is comparable to the suppressor T (Ts) cell-derived bioactive GIF in its affinity for the receptors on helper T (Th) hybridoma cells. Both naive T and B cells in normal mouse spleen lacked GIF receptors. However, presentation of specific antigen to naive T cells resulted in the expression of the receptors on activated T cells. Furthermore, activation of small resting B cells with F(ab')2 fragments of anti-mouse IgM plus IL-4, lipopolysaccharide (LPS) plus IL-4 or LPS plus dextran sulfate induced the expression of the receptors within 48 h of B cell stimulation. It was also found that NK T cells freshly isolated from mouse spleen, but not conventional NK cells, expressed receptors for GIF. CD4(+) and CD4(-) subpopulations of NK T cells showed a similar binding capability. Mature dendritic cells derived from bone marrow did not bear the receptors. The dissociation constant (Kd) of the interaction between the bioactive rhGIF mutant and the high-affinity receptors was 10-100 pM, whereas inactive wild-type rhGIF failed to bind to the receptors. A bioactive derivative of rhGIF suppressed both IgG1 and IgE synthesis by purified B cells activated by LPS and IL-4, indicating that the binding of bioactive GIF to its receptors on activated B cells results in suppression of their differentiation. (+info)
Depletion of IL-10- and TGF-beta-producing regulatory gamma delta T cells by administering a daunomycin-conjugated specific monoclonal antibody in early tumor lesions augments the activity of CTLs and NK cells.
It has been demonstrated that gamma delta T cells accumulating in early tumor lesions and those purified from spleen cells of tumor-bearing mice attenuate the activity of CTLs and NK cells. We, therefore, investigated whether depletion of gamma delta T cells from early lesions of tumors results in restoration of CTL and NK cell activities and subsequent regression of tumors. A daunomycin-conjugated anti-gamma delta TCR mAb UC7-13D5 (Dau-UC7) was prepared to efficiently deplete gamma delta T cells. An in vitro study revealed that Dau-UC7 specifically lysed gamma delta TCR+ cells and effectively inhibited splenic gamma delta T cells from tumor-bearing mice to produce cytotoxic cell-suppressive factors. Furthermore, intralesional injections of Dau-UC7 at an early stage of tumor development led to augmentation of tumor-specific CTL as well as NK cell activities and to the resultant regression or growth inhibition of the tumors. On analysis of cytokine profile, gamma delta T cells transcribed mRNAs for IL-10 and TGF-beta, but not IL-4 or IFN-gamma, suggesting the T regulatory 1-like phenotype. Finally, a blocking study with mAbs showed that the inhibitory action of gamma delta T cells on CTLs and NK cells was at least partly mediated by IL-10 and TGF-beta. These results clearly demonstrated the novel mechanism by which T regulatory 1-like gamma delta T cells suppress anti-tumor CTL and NK activities by their regulatory cytokines in early tumor formation. (+info)
Regeneration and tolerance factor: a correlate of human immunodeficiency virus-associated T-cell activation.
Human immunodeficiency virus (HIV) infection causes extensive phenotypic alterations in lymphocytes. Cellular markers that are normally absent or expressed at low levels on quiescent cells are upregulated throughout the disease course. The transmembrane form of regeneration and tolerance factor (RTF) is expressed at negligible levels on resting T cells but is quickly upregulated following in vitro stimulation and activation. Recently, we reported that expression of RTF was significantly higher in cells from HIV-seropositive (HIV(+)) individuals than in cells from HIV-seronegative (HIV(-)) individuals. Because T cells from HIV(+) individuals express markers reflecting chronic activation, we hypothesized that these in vivo-activated cells would coexpress RTF. Flow cytometry was used to assess RTF expression on activated (CD38(+) and HLA-DR(+)) CD4(+) and CD8(+) T cells. HIV(+) individuals had higher percentages of RTF(+) CD38(+) (P < 0.0001) or RTF(+) HLA-DR(+) (P = 0.0001) CD4(+) T cells than HIV(-) individuals. In HIV(+) individuals, increased percentages of CD4(+) T cells that were RTF(+), RTF(+) CD38(+), and RTF(+) HLA-DR(+) correlated inversely with the absolute number and percentage of CD4(+) T cells and correlated positively with plasma beta(2)-microglobulin concentrations. HIV(+) individuals had higher percentages of CD8(+) T cells that were RTF(+) CD38(+) (P = 0.0001) or RTF(+) HLA-DR(+) (P = 0.0010). In HIV(+) individuals, increased percentages of CD8(+) T cells that were RTF(+) HLA-DR(+) correlated inversely with the percentage of CD4(+) T cells, and high percentages of CD8(+) T cells that were RTF(+) CD38(+) correlated positively with plasma beta(2)-microglobulin levels. These findings strongly suggest that increased RTF expression is a correlate of HIV-associated immune system activation. (+info)
Differential loss of T cell signaling molecules in metastatic melanoma patients' T lymphocyte subsets expressing distinct TCR variable regions.
In this study we tested the hypothesis that loss of T cell signaling molecules in metastatic melanoma patients' T cells may affect differently T cell subsets characterized by distinct TCR variable regions. By a two-color immunofluorescence technique, expression of zeta-chain, lck, and ZAP-70 was evaluated in CD3+ T cells and in three representative T cell subsets expressing TCRAV2, TCRBV2, or TCRBV18. Partial loss of lck and ZAP-70 was found in CD3+ T cells from PBL of most melanoma patients, but not of healthy donors. The extent of zeta-chain, lck, and ZAP-70 loss depended on the TCRV region expressed by the T cells, and this association was maintained or increased during progression of disease. Coculture of patients' or donors' T cell with melanoma cells, or with their supernatants, but not with normal fibroblasts or their supernatants, down-modulated expression of zeta-chain, lck, and ZAP-70 in a TCRV region-dependent way. Immunodepletion of soluble HLA class I molecules present in tumor supernatants, but not of soluble ICAM-1, blocked the suppressive effect on T cell signaling molecule expression. T cell activation with mAbs to a single TCRV region and to CD28 led to significant and TCRV region-specific re-induction of zeta-chain expression. These findings indicate that extent of TCR signaling molecules loss in T lymphocytes from metastatic melanoma patients depends on the TCRV region and suggest that tumor-derived HLA class I molecules may contribute to induce such alterations. (+info)