species encoded by different C H genes in the germline (Stavnezer-Nordgren and Sirlin, 1986; Yancopoulos et and Piotr Zelazowski* *Department of Pathology al., 1986). Germline C H RNAs are spliced products of distinct I exons, located 5Ј to every S region, and the The Uniformed Services University of the Health Sciences immediate 3Ј C H gene (Figure 1). Transcription initiates within a promoter 5Ј to the I exon, proceeds through Bethesda, Maryland 20814 † Department of Biochemistry and Cell Biology the S region, and terminates at the 3Ј end of the C H gene.

SumrlrlaryA number of distinct functional abnormalities have been observed in B ceils derived from pS0/ NF-KB or c-rel knockout mice. RelB, another member of the NF-KB/Rel family of transcription factors, is expressed during the latter stages of B cell maturation and can bind to regulatory sites within the Ig heavy chain locus. Therefore, we tested the ability of B ceils from relB knockout mice (relB -/-) to proliferate, undergo maturation to IgM secretion, and switch to the expression of downstream Ig isotypes in response to distinct activators including LPS, anti-CD40 mAb or CD40 ligand, and/or dextran anti-IgD antibodies in combination with various cytokines, including IL-4, IL-5, IFN-3', and TGF-13. B cells lacking RelB showed up to 4-fold reductions in DNA synthesis in response to LPS, CD40, and membrane Ig-dependent activation relative to controls. However, relB -/-B cells were comparable to control B cells in their ability to undergo maturation to IgM secretion and switch to the expression of IgG3, IgG1, IgG2b, IgG2a, IgE, and/or IgA under all activation conditions tested. Thus, RelB, like c-Rel and p50/NF-KB, plays a role in B cell proliferation. However, in contrast to c-Rel and p50/ NF-KB, it is not critically involved in maturation to Ig secretion or expression oflg isotypes.

A role for IL-10 in regulating Ig isotype switching directly at the level of the murine B cell has not been previously reported. In this report we show that IL-10 selectively up-regulated IgM to IgG3 class switching in lipopolysaccharide (LPS)-activated cultures through a direct effect on membrane (m) IgM+IgG3(-)B cells in vitro. IL-10 stimulated a 3- to 4-fold enhancement (from 6-8 to 20-30%) in membrane mIgG3(+) cells and a significant increase in Smu-Sgamma3 DNA rearrangement events as measured by digestion-circularization PCR (DC-PCR) over that observed with LPS alone. IL-10 induction of switching to IgG3 was not accompanied by a corresponding increase in the steady-state levels of germline CHgamma3 RNA. By contrast, IL-10 strongly inhibited the transforming growth factor-beta-mediated generation of mIgA+ cells and Smu-Salpha DNA rearrangement events in LPS-, but not CD40 ligand (CD40L)-activated B cells. This effect was not accompanied by changes in the steady-state levels of germline CHalpha RNA. IL-10 had no effect on IL-4-mediated switching to either IgG1 or IgE in either LPS- or CD40L-activated B cells. Thus, IL-10 can either enhance or suppress switching to particular murine Ig isotypes but it differs from most other murine cytokines in that its effects on switching do not appear to be associated with changes in the corresponding steady-state levels of germline CH RNA.

No abstract

No abstract