Characterisation of T follicular helper cells (Tfh) in human nasopharynx-associated lymphoid tissue and effect of CpG-DNA on TFH-mediated antibody production

Considering the importance of T follicular helper cells (T_FH) for B cell antibody response, novel adjuvants to boost T_FH function may be an attractive vaccination strategy. Adenotonsillar tissues are major component of nasopharynx-associated lymphoid tissue(NALT) and important in mediating immunity to respiratory pathogens. We studied T_FH in human NALT and effect of CpG-DNA on T_FH-mediated B cell immunity. Adenotonsillar MNC were stained for T_FH markers including CD4⁺ CXCR5^high ICOS^high by and intracellular cytokine staining. Purified T_FH and non-T_FH cells were co-cultured with B cells in the presence of influenza antigen and CpG-DNA. Purified pDC were added to T_FH-B cell co-culture to study their importance in T_FH cell-mediated response. Haemagglutinin (HA)-specific antibody production was analysed. We have found a prominent number of T_FH in human NALT considerably higher than in PBMC. There was an age-associated decrease in T_FH frequency in NALT. T_FH in NALT were shown to express IL-4, IL-10 and IL-21. A good correlation between GC B cell and T_FH cell was seen. Co-culture of purified T_FH but not non-T_FH with B cells promoted antibody production. Stimulation by CpG-DNA increased T_FH and that was correlated with HA-specific antibody production following influenza antigen stimulation. Co-incubation T_FH-B cell with pDC enhanced the antibody production. Blocking IL-21R reduced T_FH that was correlated with reduction of HA-specific antibody production. Enhancing vaccine immunogenicity through modulation of T_FH numbers or function in human NALT using modern adjuvants such as CpG-DNA may be an effective vaccination strategy against respiratory pathogens.