SummaryInterleukin 10 (IL-10) and viral Ibl0 (v-IL-10) strongly reduced antigen-specific proliferation of human T cells and CD4 + T cell clones when monocytes were used as antigen-presenting cells. In contrast, IL-10 and v-Ibl0 did not affect the proliferative responses to antigens presented by autologous Epstein-Barr virus-lymphoblastoid cell line (EBV-LCL). Inhibition of antigen-specific T cell responses was associated with downregulation of constitutive, as well as interferon 3'-or Ib4-induced, class II MHC expression on monocytes by IL-10 and v-Ibl0, resulting in the reduction in antigen-presenting capacity of these ceUs. In contrast, IL-10 and v-Ibl0 had no effect on class II major histocompatibility complex (MHC) expression on EBV-LCL. The reduced antigenpresenting capacity of monocytes correlated with a decreased capacity to mobilize intracellular Ca 2 + in the responder T cell clones. The diminished antigen-presenting capacities of monocytes were not due to inhibitory effects of II.-10 and v-Ibl0 on antigen processing, since the proliferative T cell responses to antigenic peptides, which did not require processing, were equaUy well inhibited. Furthermore, the inhibitory effects of Ibl0 and v-IL-10 on antigen-specific proliferative T cell responses could not be neutralized by exogenous Ib2 or Ib4. Although IL-10 and v-IL-10 suppressed IL-lc~, IL-1B, tumor necrosis factor ot (TNF-c~), and IL-6 production by monocytes, it was excluded that these cytokines played a role in antigen-specific T cell proliferation, since normal antigenspecific responses were observed in the presence of neutralizing anti-Ibl, -IL-6, and -TNF-tx mAbs. Furthermore, addition of saturating concentrations of IL-lot, IL-I~, IL-6, and TNF-o~ to the cultures had no effect on the reduced proliferative T cell responses in the presence of Ibl0, or v-Ibl0. Collectively, our data indicate that IL-10 and v-IL-10 can completely prevent antigen-specific T cell proliferation by inhibition of the antigen-presenting capacity of monocytes through downregulation of class II MHC antigens on monocytes.

Interleukin 10 (IL-10), originally identified as a TH2 helper T-cell product able to inhibit cytokine production by THI cells, is highly homologous to BCRF1

In these studies, IFN gamma-inducing factor (IGIF), unlike IL-12, did not drive Th1 development in BALB/c or C57BL/6 mice, but like IL-1alpha, potentiated IL-12-driven Th1 development in BALB/c mice. IGIF and IL-12 synergized for IFN gamma production from Th1 cells. Unlike IL-1alpha, IGIF had no effect on Th2 cells. IGIF signaled through IRAK, IL-1 receptor-associated kinase, to induce nuclear translocation of p65/p50 NFkappaB in Th1 cells. IL-1alpha had no effect on proliferation, cytokine production, or NFkappaB activation in Th1 cells but activated NFkappaB and proliferation in Th2 cells. Thus, Th1 and Th2 cells may differ in responsiveness and receptor expression for IL-1 family molecules. IGIF and IL-1alpha may differentially amplify Th1 and Th2 effector responses, respectively.

We have demonstrated the existence of human cytokine synthesis inhibitory factor (CSIF) [interleukin 10 (IL-10)]. cDNA clones encoding human IL-10 (hIL-10) were isolated from a tetanus toxin-specific human T-cell clone. Like mouse IL-10, hIL-10 exhibits strong DNA and amino acid sequence homology to an open reading frame in the EpsteinBarr virus, BCRFI. hIL-lO and the BCRFI product inhibit cytokine synthesis by activated human peripheral blood mononuclear cells and by a mouse Thl clone. Both hIL-10 and mouse IL-1O sustain the viability of a mouse mast cell line in culture, but BCRFI lacks comparable activity in this assay, suggesting that BCRFI may have conserved only a subset of hIL-10 activities.

SummaryHighly purified, small dense splenic B cells from unstimulated mice showed increased expression ofclass II major histocompatibility complex (MHC) antigens and enhanced viability when cultured with affinity-purified recombinant interleukin 10 (HIA0), compared with B cells cultured in medium alone. These responses were blocked by a monoclonal antibody (mAb) specific for 11,10, but not by an isotype-matched control antibody. IL10 did not upregulate the expression of Fce receptors (CD23) or class I MHC antigens on small dense B cells or induce their replication as monitored by [3H]thymidine incorporation. While these B cell-stimulatory properties of IWO are also mediated by ID4, the two cytokines appear to act independently in these assays ; anti-IL10 antibodies blocked 1140 but not I14-mediated B cell viability enhancement, and vice versa. Similarly, since IIr4 upregulates CD23 on small dense B cells, the inability of IIr10 to do so argues against its acting via endogenously generated 114. Finally, IIA0 did not upregulate class II MHC antigens on B cells from X chromosome-linked immunodeficiency (XID) mice, while the same cells showed normal upregulation of class II antigens in response to 11.4. This report also extends our understanding of the relationship between IIA0 and the highly homologous Epstein-Barr virus (EBV)-encoded Barn HI fragment C rightward reading frame no. 1 (BCRFI) protein. It has previously been shown that BCRFI protein exhibits the cytokine synthesis inhibitory activity of IL10. This report indicates that BCRFI protein also enhances in vitro B cell viability, but does not upregulate class II MHC antigens on B cells. One explanation for these data is that 111,10 contains at least two functional epitopes, only one ofwhich has been conserved by EBV Blymphocytescontribute to the immune response by their production of specific antibodies in response to antigenic stimuli. This process is regulated by a subset of soluble glycoproteins collectively termed cytokines (1-3). The precise number of cytokines involved and their modes of action require further clarification. 11,10 (originally designated cytokine synthesis inhibitory factor [CSIF]l; 4) is a cytokine produced by activated type 2 T helper (Th2) cells (4, 5) and B cells (6, 7), which has the property ofsuppressing cytokine production by type 1 T helper (Thl) cells (4). Isolation of the cDNA for mouse RAO (8) revealed a striking homology between ' Abbreviations used in this paper: BCRFI, BamHI fragment C rightward reading frame no. 1 ; CSIF, cytokine synthesis inhibitory factor; MTT, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide; SA, streptavidin; Thl/Th2, type 1/type 2 T helper cells; XID, X chromosome-linked immunodeficiency. this cytokine and a previously uncharacterized open reading frame, designated BamHI fragment C rightward reading frame no. 1 (BCRFI), in the EBV genome. Subsequent expression and testing of the protein encoded by BCRFI revealed that this molecule also mediated suppression of Thl cytokine production (...