Annamalai and Selvaraj have reported in birds that following receipt of a coccidial vaccine, the mRNA level of CXCR5 in some specific organs increased substantially [29]. Also Guo et al. have shown that fusion of a vaccine antigen directly to CXCL13 could enhance DNA vaccine potency [30].

Thus, the GSK1120212 in vivo linkage of CXCR5, CXCL13 polymorphisms to HBV vaccine efficacy is consistent with these other studies indicating that TfH cells played a critical role in antibody production. The majority of previous studies have suggested that circulating CXCR5+CD4+ T cells have the essential features similar to the TfH cells from lymphoid organs [31] and [32]. So we compared the CXCR5 positive populations in CD3+CD4+ T cells or CD3−CD19+ B cells in peripheral blood from different genotype populations. In an attempt to demonstrate an association between the SNPs in the 3′-UTR (rs3922 and rs676925) and

gene expression level, 29 healthy volunteers were recruited and genotyped. This was necessary because of the paucity of RNA or PBMCs from the responders and non-responders to HBV vaccination making up the study cohort. Individuals with rs3922 “GG” genotype had a higher CXCR5 expression level in the blood OSI-906 mouse than “non-GG” groups. This observation was concordant with our luciferase assays and hence the data suggested that “G” allele may correlate with a relative high gene expression. In the current study, a role for miR-558 was excluded and the detailed mechanism by which the “G” allele favors CXCR5 gene expression remains unknown. It appears counter-intuitive that the “G” allele, which is associated with the non-responder phenotype, should isothipendyl correspond to a higher expression of CXCR5. However, it remains unclear whether higher CXCR5 expression on TfH cells will enhance their B cell help function. In fact, Bentebibel et al. have reported that, in human tonsils, the CD4+ subset (CXCR5loCD4+) expressing low levels of CXCR5 secreted more IL-21 and IL-10 than the high expression subset (CXCR5hi). They also appeared to provide more efficient help for the differentiation of naive B cells into Ig-producing cells outside the germinal

center [33]. Overall, this study supports the idea that polymorphisms in CXCR5 and CXCL13, two of TfH associated genes, are closely related to the non-responsiveness to HBV vaccination. The restricted number of non-responsive individuals in our cohort population and the consequent limitation in the availability of blood samples precluded further investigation of how the polymorphisms in CXCR5 and CXCL13 might affect the functioning of these genes. Therefore, how the expression levels of these genes can affect the efficacy of HBV vaccination is still a puzzle. However, achieving a better understanding of the functions of CXCR5 and CXCL13, particularly in response to HBV vaccination, may provide clues that can facilitate optimization of HBV vaccines.