T follicular helper (TFH) cells are a subset of CD4+ T cells that produce IL-4 and IL-21 and drive B cell maturation and clonal expansion into antibody-secreting plasma cells, the key to IgE-mediated allergic responses. TFH and B cell interactions are regulated by T follicular regulatory (TFR) cells. Although effective in grass pollen allergics (GPA), allergen-specific immunotherapy (AIT), administered subcutaneously (SCIT) or sublingually (SLIT) is associated with adverse events. Thus, warranting the need for alternative approaches. This thesis aims to evaluate the role of and enumerate circulating CXCR5+PD-1+ TFH cells and TFR cells in GPA, non-atopic healthy controls (NAC) and AIT-treated patients. Isolated naïve and memory B cells were stimulated with IL-4 and IL-21 to investigate their effect on germinal centre (GC) reactions, B cell class-switching and differentiation.
TFH cells were shown to be distinct from TH2 and TH2A cells and capable of secreting IL-4 and IL-21. IL-4 alone promotes GC responses and B cell class-switching; and drives plasma cell differentiation and IgE+ cells in the presence of IL-21. Enumeration of TFH cell subsets in a cross-sectional study demonstrated high TFH cells in GPA compared to NAC, which was lower in SCIT and SLIT. Furthermore, TFR cells were induced in SCIT and SLIT and differential chromatin accessibility was observed in TFH and TFR cells from all groups. In a separate RDBPC study, the administration of short-course peptide immunotherapy attenuated proportion of TFH cell subsets and induced TFR cells, which persisted until the end of the grass pollen season. Additionally, in vitro stimulation study of depigmented (DPG Phl p) and DPG-polymerised (DPG-POL Phl p) depigoids, demonstrated a lower proliferation of TFH cell subsets in response to DPG-POL Phl p compared to the native protein and DPG Phl p.
Collectively, these findings demonstrated the role of TFH cells in the pathomechanism of seasonal allergic rhinitis (SAR) and TFR cells induction following SCIT and SLIT, underscored by changes in the chromatin landscape. Peptide immunotherapy and polymerised depigoids are associated with modulation of TFH and TFR cells, highlighting their potential use that is safe and effective.