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

The effect of human recombinant interleukin 4 (IL-4) on antibody production by normal peripheral blood mononuclear cells enriched for B cells was investigated.

CD40 is an integral membrane protein found on the surface of B lymphocytes, dendritic cells, follicular dendritic cells, hematopoietic progenitor cells, epithelial cells, and carcinomas. It is a 45-50 kDa glycoprotein of 277 aa, which is a member of the tumor necrosis factor receptor superfamily. The CD40 gene maps to human chromosome 20q11-2-q13-2. CD40 binds to a ligand (CD40-L) which is an approximately 35 kDa glycoprotein of 261 aa, a member of the tumor necrosis factor superfamily. The CD40-L gene maps to human chromosome Xq24. This CD40-L is expressed on activated T cells, mostly CD4+ but also some CD8+ as well as basophils/mast cells. The CD40-L is defective in the X-linked hyper-IgM syndrome. Cross-linking of CD40 with immobilized anti-CD40 or cells expressing CD40-L induces B cells to proliferate strongly, and addition of IL-4 or IL-13 allows the generation of factor-dependent long-term normal human B cell lines and the secretion of IgE following isotype switching. Addition of IL-10 results in very high immunoglobulin production with limited cell proliferation. IL-10 induces naive B cells to produce IgG3, IgG1, and IgA1, and further addition of TGF beta permits the secretion of IgA2. Several evidences suggest that CD40-dependent activation of B cells is important for the generation of memory B cells within the germinal centers: (i) CD40 activated germinal center B cells cultured in the presence of IL-4 acquire a memory B cell phenotype, (ii) CD40 activated B cells can undergo isotype switching, (iii) the deficit of CD40-L results in the hyper-IgM syndrome characterized by lack of germinal centers in secondary lymphoid organ follicles and lack of IgG, IgA, and IgE, and (iv) CD40-L positive T cells are present in secondary follicles. Thymic epithelial cells, activated monocytes, and dendritic cells express CD40 antigen which may be involved in an enhanced cytokine production by these cells, allowing an amplification of T cell proliferation. Finally, as other members of the tumor necrosis factor receptor family have been shown to bind several ligands, it is possible that CD40 may bind other ligands that may trigger CD40 on different cell types such as hematopoietic cells or epithelial cells.

We investigated the involvement of mitogen-activated protein kinases (MAPKs) in the maturation of CD83− dendritic cells (DC) derived from human blood monocytes. Maturating agents such as LPS and TNF-α induced the phosphorylation of members of the three families of MAPK (extracellular signal-regulated kinase l/2, p46/54 c-Jun N-terminal kinase, and p38 MAPK). SB203580, an inhibitor of the p38 MAPK, but not the extracellular signal-regulated kinase l/2 pathway blocker PD98059, inhibited the up-regulation of CD1a, CD40, CD80, CD86, HLA-DR, and the DC maturation marker CD83 induced by LPS and TNF-α. In addition, SB203580 inhibited the enhancement of the allostimulatory capacity and partially prevented the down-regulation of FITC-dextran uptake induced by LPS and TNF-α. Likewise, SB203580 partially prevented the up-regulation of IL-1α, IL-1β, IL-lRa, and TNF-α mRNA upon stimulation with LPS and TNF-α, as well as the release of bioactive TNF-α induced by LPS. DC maturation induced by the contact sensitizers 2,4-dinitrofluorobenzene and NiSO4, as seen by the up-regulation of CD80, CD86, and CD83, was also coupled to the phosphorylation of p38 MAPK, and was inhibited by SB203580. The irritants SDS and benzalkonium chloride that do not induce DC maturation did not trigger p38 MAPK phosphorylation. Together, these data indicate that phosphorylation of p38 MAPK is critical for the maturation of immature DC. These results also suggest that p38 MAPK phosphorylation in DC may become useful for the identification of potential skin contact sensitizers.

SummaryIn the present report, we have investigated the in vitro differentiation of surface(s) slgD + and slgD-human B cells into Ig-secreting calls in response to various stimuli, slgD + B cells homogeneously expressed some of the antigens identifying mantle zone B cells, but lacked expression of germinal center markers, thus confirming that the B cell populations positively selected on the basis of slgD expression were highly enriched for naive B lymphocytes. Conversely, slgD-B cells expressed some of the antigens spedfically associated with germinal center B cells. T cell-independent differentiation of slgD + and sIgD-B cells could be achieved by simultaneous crosslinking of sIgs and CD40 in the presence of a mouse Ltk-cell line stably expressing human CDw32/Fc'yPdI (CDw32 L cells). In this experimental system, sIgD + B cells were exclusively proned for IgM synthesis, whereas sIgD-B ceils produced IgG, IgM, and IgA. Both the human and viral forms of interleukin 10 (ILd0) strongly increased the Ig secretion by sIgD + and slgD-B cells simultaneously activated through slgs and CD40. IgM and IgG constituted the predominant Ig isotype produced by slgD + and slgD-B cells, respectively, in response to IL-10. slgD + B cells could be induced for IgA synthesis upon co-culturing with transforming growth factor (TGF-~) and II.-10, in the presence of an anti-CD40 monodonal antibody presented by the CDw32 L cells. In contrast, TGF-~ suppressed the IL-10-mediated IgG, IgM, and IgA secretions by slgD-B cells, slgD + B cells could not be induced for IgA synthesis by TGF-~ and Ibl0 after crosslinking of their slgs, suggesting that ligation of CD40 was one of the obligatory signals required for commitment of naive B cells to IgA secretion. Limiting dilution experiments indicated that the IgA-potentiating effect of TGF-B was due to its capacity to increase the frequency of IgA-producing cells, most likely as a consequence of class switching. Taken together, our data strongly suggest that TGF-B is involved in the regulation of IgA isotype selection in humans.