Production of antigen-specific immunoglobulins in tissues is controlled by follicular helper T (Tfh) cells, which are recognized as memory Tfh cells in peripheral blood. Recent studies have revealed that inducible T-cell co-stimulator (ICOS) and programmed death 1 (PD-1) are activation molecules in blood Tfh cells. However, the role of blood Tfh cells expressing such molecules in the pathogenesis of birch pollen allergy remains unknown.
Patients with birch pollen allergy (n = 34) and healthy controls (n = 21) were recruited in this study. Expression of ICOS and PD-1 in blood Tfh cells from subjects in pollen and pollen-free seasons (i.e. before and after the periods with pollens) was examined by flow cytometry. Correlations between results of flow cytometry and clinical parameters were also analyzed.
Levels of ICOS+ and/or PD-1+ in blood Tfh cells in the patients were similar to those in the controls throughout the pollen-free seasons, whereas the percentages of ICOS+ blood Tfh cells during the pollen season were temporarily increased in the patients compared to those in the controls. We also found that total symptom scores were significantly correlated with percentage of ICOS+ blood Tfh cells. Moreover, differential levels of ICOS+ blood Tfh cells in pollen- and pollen-free seasons were significantly correlated with those of birch pollen-specific IgE.
Our findings suggest that increase in ICOS+ blood Tfh cells in response to exposure to birch pollen may underlie the pathogenesis of birch pollen allergy.