Sun, Jie

Abstract IFN regulatory factor 4 (IRF4) is a key transcription factor that promotes effector CD8+ T cell differentiation and expansion. The roles of IRF4 in regulating the CD8+ T cell response to cytokines have not been explored. In this article, we show that IL-2 and IL-15 signaling and STAT5 activation regulate IRF4 expression in CD8+ T cells. Gene-expression profile analysis has also revealed that IRF4 is required for expression of the receptors of IL-2 family cytokines CD122 and CD127. We found that IRF4 binds directly to CD122 and CD127 gene loci, indicating that it may directly promote CD122 and CD127 gene transcription. As a consequence, IRF4-deficient CD8+ T cells show diminished sensitivity to IL-2, IL-15, and IL-7 treatment in vitro. Furthermore, we found that IRF4-deficient CD8+ T cells had lower expression of CD122 and CD127 in vivo during influenza virus infection. These data suggest that IRF4 regulates the sensitivity of CD8+ T cells to IL-2 family cytokines, which correlates with the diminished effector and memory CD8+ T cell responses in IRF4-deficient CD8+ T cells.

Abstract Follicular Th (Tfh) cells are a distinct subset of Th cells that help B cells produce class-switched antibodies. Studies have demonstrated that Tfh cells are highly prone to HIV infection and replication. However, the molecular mechanisms underlying this phenomenon are largely unclear. Here, we show that murine and human Tfh cells have diminished constitutive expression of IFN-stimulated genes (ISGs) inclusive of antiviral resistance factor MX dynamin-like GTPase 2 (MX2) and IFN-induced transmembrane 3 (IFITM3) compared with non-Tfh cells. A lower antiviral resistance in Tfh was consistent with a higher susceptibility to retroviral infections. Mechanistically, we found that BCL6, a master regulator of Tfh cell development, binds to ISG loci and inhibits the expression of MX2 and IFITM3 in Tfh cells. We demonstrate further that inhibition of the BCL6 BR-C, ttk, and bab (BTB) domain function increases the expression of ISGs and suppresses HIV infection and replication in Tfh cells. Our data reveal a regulatory role of BCL6 in inhibiting antiviral resistance factors in Tfh cells, thereby promoting the susceptibility Tfh cells to viral infections. Our results indicate that the modulation of BCL6 function in Tfh cells could be a potential strategy to enhance Tfh cell resistance to retroviral infections and potentially decrease cellular reservoirs of HIV infection.

SUMMARYANCA directed against PR3 are highly specific for Wegener's granulomatosis and microscopic polyangiitis, and have been implicated in the pathogenesis of small vessel vasculitis. Most PR3-ANCA are directed against conformational epitopes on PR3. This study was designed to determine whether the cleavage of the N-terminal activation dipeptide of PR3 is required for the binding of PR3-ANCA. Recombinant PR3 (rPR3) variants were expressed in the epithelial cell line, 293. As confirmed by radiosequencing, the rPR3 secreted into the 293 cell culture supernatant is N-terminally unprocessed. Two enzymatically inactive rPR3 mutants were expressed in 293 cells: rPR3-S176A and δ-rPR3-S176A. rPR3-S176A contains the N-propetide Ala-2-Glu-1, δ-rPR3-S176A does not. Culture supernatants of rPR3-S176A and δ-rPR3-S176A expressing 293 cells were used as sources of target antigen for PR3-ANCA testing by capture ELISA. Forty unselected consecutive PR3-ANCA+ sera were tested. With δ-rPR3-S176A as antigen all 40 were recognized, compared with only 34 of 40 when rPR3-S176A served as target antigen. The majority of the serum samples contained a mixture of antibodies reacting with epitopes accessible on the mature and on the proform of PR3. In conclusion, the cleavage of the N-terminal activation dipeptide of PR3 is not an absolute requirement for recognition by all PR3-ANCA. However, a substantial proportion of PR3-ANCA recognize (a) target antigen(s) exposed only after the conformational change of PR3 associated with the N-terminal processing. In 15% of sera this PR3-ANCA subset occurred exclusively. PR3-ANCA subtypes can be differentiated using specifically designed rPR3 variants as target antigens, and non-haematopoietic mammalian cells without regulated secretory pathway can be used for their expression.