Background: The role of T follicular helper (Tfh) cells in schistosome infection is not fully defined. In a previous study, a higher frequency of circulating PD-1(+)CXCR5(+)CD4(+) Tfh cells was observed in patients with chronic schistosomiasis relative to healthy controls (HCs) and it correlated positively with the level of soluble egg antigen (SEA) specific antibodies in serum. However, the function of Tfh cells in patients with acute schistosomiasis remains elusive; this was investigated in the present study.
Methods: The frequency of circulating Tfh cells and the expression of inducible T cell co-stimulator (ICOS), programmed cell death 1 (PD-1) and B cell subsets were analyzed in 12 patients with acute schistosomiasis and 10 HCs by flow cytometry. The expression of Bcl6, c-Maf and IL-21 mRNA were detected by quantitative real-time reverse transcriptase PCR (qRT-PCR). The concentration of serum IL-21 and IgG specific to Schistosoma japonicum antigen were then determined by enzyme linked immunosorbent assay (ELISA). Correlations between PD-1(+)CXCR5(+)CD4(+) Tfh cells, memory B cells and IgG specific to S. japonicum were analyzed by Spearman's rank correlation.
Results: The frequency of PD-1(+)CXCR5(+)CD4(+) Tfh and memory B cells was increased in acute schistosomiasis patients relative to HCs. Moreover, the levels of IL-21 in serum and the expression of IL-21 mRNA were higher in acute schistosomiasis patients. However, there was no significant correlation between PD-1(+)CXCR5(+)CD4(+) Tfh cells, memory B cells and IgG specific to S. japonicum antigen in patients with acute schistosomiasis.
Conclusions: PD-1(+)CXCR5(+)CD4(+) Tfh cells in peripheral blood are involved in the immune response of patients with acute schistosomiasis. Understanding the immunological mechanism is helpful for the development of vaccination strategies to control schistosomiasis.
Keywords: Acute schistosomiasis; IL-21; PD-1; T follicular helper cells.