There is increasing interest recently in developing intranasal vaccines against respiratory tract infections. Antibody response is critical in vaccine-induced protection and TFH is considered important in mediating antibody response. Most data supporting the role for TFH in antibody response are from animal studies, and direct evidence from humans is limited, apart from TFH-like cells in blood. We studied activation and induction of TFH and its role on anti-influenza antibody response by live-attenuated influenza vaccine(LAIV) in human nasopharynx-associated lymphoid tissue(NALT). TFH activation in adenotonsillar tissues were analysed by flow-cytometry, and anti-hemagglutinin(HA) antibodies examined following LAIV stimulation of tonsillar mononuclear cells(MNC). Induction of antigen-specific TFH by LAIV was studied by flow-cytometry for induced TFH and CD154 expression. LAIV induced TFH proliferation which correlated with anti-HA antibody production, and TFH was shown critical for antibody response. Induction of TFH from na?ve T cells by LAIV was shown in newly induced TFH expressing BCL6 and CD21, which was followed by the detection of anti-HA antibodies. Antigen specificity of LAIV-induced TFH was demonstrated by the expression of antigen-specific T cell activation marker CD154 upon challenge by H1N1 virus antigen or HA. LAIV-induced TFH differentiation was inhibited by BCL6, IL21, ICOS and CD40 signalling blocking respectively, and that diminished anti-HA antibody production.

CONCLUSION: We demonstrate for the first time the induction of antigen-specific TFH by LAIV in human NALT that provide critical support for anti-influenza antibody response. Promoting antigen-specific TFH in NALT by intranasal vaccines may provide an effective vaccination strategy against respiratory infections in humans.IMPORTANCE. Airway infection such as influenza is common in humans. Intranasal vaccination has been considered a more biologically relevant and effective way of immunization against airway infection. Vaccine-induced antibody response is crucial for protection against infection. Recent data from animal studies suggest one type of T cells, named TFH is important for the antibody response. However, data on whether this TFH-mediated help for antibody production operates in humans is limited, due to the lack of access to human immune tissue containing the TFH In this study, we demonstrated the induction of TFH cells by an intranasal influenza vaccine in human immune tissue that provide critical support for anti-influenza antibody response. Our findings provide direct evidence that TFH cells play a critical role in vaccine-induced immunity in humans, and suggest a novel strategy to promote such cells by intranasal vaccines against respiratory infections.