Abstract:
Follicular helper T (Tfh) cells, a newly characterized effector T helper cell subset, are mainly found in B cell follicles of secondary lymphoid organs. Tfh cells are effector cells which provide help for antibodies production and for B cell differentiation. Tfh subset can be distinguished from other helper T cell subsets by the use of CXCR5 and ICOS expression. Notch signaling pathway is a well conserved pathway operating in various organisms and functioning in controlling many cellular processes. Previous study on gene expression in Tfh cells by microarray analysis showed that these cells expressed Notch signaling related genes. However, the expression profiles of Notch receptors and the effect of inhibition of Notch signaling on the effector functions in Tfh cells have not been studied. In this study, we investigated the expression profiles of Notch receptors and its target genes in Tfh cells isolated from human tonsils. Expression of Notch1-4 and two Notch target genes were investigated by quantitative RT-PCR. Notch1-3, DTX1 and Hes1 were expressed in Tfh cells but the expression of Notch4 was not detectable. More importantly, Notch1, Notch3 and Hes1, are found to be expressed significantly higher than the control non-Tfh population. Next, we investigated the effect of inhibition of Notch signaling on Tfh cells function using gamma secretase inhibitor (GSI). Expressions of Bcl-6, one of essential genes regulating Tfh functions were significant lower in GSI treated cells than the control. We next investigated the ability of Tfh cells subset to induce IgG secretion of B cells. We found no difference in IgG production between GSI treated Tfh and the control group. Taken together, these results strongly suggested that Notch signaling is involved in effector function of human Tfh.
