UCSF

The studies in this work are centered around two projects. The first two chapters are composed of background and primary research on the role of microRNAs (miRNAs) in B cell class switch recombination. MiRNAs regulate cell fate decisions by post-transcriptionally tuning networks of mRNA targets. We utilized miRNA-directed pathway discovery to reveal a regulatory circuit that influences B cell activation and immunoglobulin class switch recombination (CSR). We developed a system to deplete mature, activated B cells of miRNAs, and performed a rescue screen that identified the miR-221/222 family as a positive regulator of CSR. Endogenous miR-221/222 regulated B cell proliferation and CSR to IgE and IgG1 in vitro, and miR-221/222-deficient mice exhibited defective IgE production in allergic airway challenge and polyclonal B cell activation models in vivo. We combined comparative Ago2-HITS-CLIP and gene expression analyses to identify mRNAs bound and regulated by miR-221/222 in primary B cells. Interrogation of these putative direct targets uncovered functionally relevant downstream genes. Genetic depletion or pharmacological inhibition of Foxp1 and Arid1a confirmed their roles as key modulators of CSR to IgE and IgG1. The third chapter is in the study of TLR9 co-signaling in the germinal center (GC) B cell response. It was previously unknown how co-signaling events through innate immune system receptors in B cells positively influenced the generation of GC B cells. In this chapter we addressed this question through transcriptomics to find that signaling and activation from TLR9-containing antigen increased Myc and mTORC signatures that bolstered the GC B cell response.