Both groups of chimeras had comparable proportions and numbers of B, CD4+ and CD8+ T cells (data not shown)

Both groups of chimeras had comparable proportions and numbers of B, CD4+ and CD8+ T cells (data not shown). sequence-specific base pairing with target mRNAs initiating inhibition of Cambendazole translation or degradation of the mRNA. In animals, miRNAs are transcribed as primary miRNA (pri-miRNA). The pri-miRNA are processed in the nucleus to precursor miRNA (pre-miRNA) by the microprocessor complex prior to their transport into the cytoplasm. In the cytoplasm, they are further processed to mature miRNAs by Dicer and incorporated into the RNA-induced silencing complex. (reviewed by (Bartel, 2004)). T-cell specific deletion of Dicer has revealed a role for this enzyme in thymic development and the differentiation of T lymphocytes (Cobb et al., 2006; Cobb et al., 2005; Muljo et al., 2005; Neilson et al., 2007). Although these data imply miRNAs may be important in lymphocyte development, essential functions for individual miRNAs have not yet emerged. MiR-155 is contained within the non-coding B cell integration cluster (was first identified Cambendazole as a frequent site of integration for the avian leukosis computer virus and co-expression of bic with c-myc has Cambendazole been found to synergize for lymphomageneis (Tam et al., 1997). In humans, high expression of and miR-155 has been shown in Hodgkins lymphoma, primary mediastinal B-cell lymphoma and diffuse large B-cell lymphoma, while very low expression of and miR-155 were reported in adult Burkitt lymphoma (Eis et al., 2005; Metzler et Rabbit Polyclonal to CCRL2 al., 2004; van den Berg et al., 2003). When over-expressed as a transgene in B cells miR-155 gives rise to pre-B cell lymphomas (Costinean et al., 2006). In untransformed cells of the immune system Bic transcripts and miR-155 expression appear to be induced by antigenic stimulation (Haasch et al., 2002; Rodriguez et al., 2007). is also expressed by macrophages following Toll-like receptor and type-I interferon stimulation (OConnell et al., 2007); and in B cells following treatment with antibodies to surface IgM (van den Berg et al., 2003). Furthermore, a subset of human CD20 positive cells within the germinal center has been shown to express by RNA hybridization (van den Berg et al., 2003). Previous studies show that miR-155 mutant mice display defective B and T cell immunity and abnormal function of antigen presenting cells (Rodriguez et al., 2007; Thai et al., 2007). Moreover, a reduced number of germinal centre B cells was observed in miR-155 deficient mice, whereas its over-expression led to the opposite phenotype (Thai et al., 2007). Neither of these studies identified the cellular basis of the defects in vivo. Both studies used miR-155 germ line mice and the conditional expression of miR-155 was driven by Cre under the control of the CD21 promoter. Thus, expression of miR155 was targeted to both B cells and follicular dendritic cells (Victoratos et al., 2006). Here we show that defects in humoral immunity following primary and secondary immunization are intrinsic to B lymphocytes. Microarray analysis of B cells activated under conditions that promote class switching to IgG1 revealed miR-155 regulates expression of many genes, a substantial fraction of which are predicted to be direct targets of miR-155. One of these genes was (encoding the transcription factor Pu.1) which has a highly conserved functional miR-155 binding site in its 3UTR. Moreover, Pu.1 is highly expressed in miR-155 deficient B cells and Pu.1 over-expression in wild type B cells results in reduced numbers of IgG1 switched cells. Our results indicate that miR-155 plays a key role in antigen-driven B cell maturation and the persistence and/or differentiation of Ig class switched cells and that deregulation of Pu.1 is likely to be a contributing factor to the phenotype observed in miR-155-deficient mice. Results Deficiency in miR-155 leads to impaired primary and secondary immune response It has been previously shown that miR-155 is usually dispensable for lymphocyte development but necessary for the generation of T and B cell responses (Rodriguez et al., 2007; Thai et al., 2007). To further understand the role of miR-155 in regulating the function of B cells we studied the requirement of miR-155 for T-independent type-I (TI-1) responses by immunizing mice with the dinitrophenylated lypopolysaccharide (DNP-LPS). We observed defective switched antibody responses at day 7 after immunization (Physique 1A). By contrast, the production of antigen-specific IgM was normal. Open in a separate window Physique 1 miR-155 deficient mice produce reduced amounts of low affinity IgG1 antibodies(A) Wild type (open squares) or miR-155 deficient chimeric mice (filled triangles) were immunized with DNP-LPS and anti-DNP specific antibody titers were measured 7 days later. * corresponds to and the common cytokine receptor gamma chain (mice), as previously described (Huntington.