Impairment of antigen-presenting function of peripheral γδ T cells in patients with sepsis

Impairment of antigen-presenting functions is a key mechanism contributing to sepsis-induced immunosuppression. Recently, γδ T cells have been demonstrated as professional antigen-presenting cells (APCs); however, their role in sepsis remains unknown. In this in vitro study, the APC function of human peripheral γδ T cells was assessed using samples collected from 42 patients with sepsis and 27 age-matched healthy controls. The APC-related markers HLA-DR, CD27, CD80, and CCR7 on fresh γδT cells were significantly higher in patients with sepsis compared with matched controls; however, they responded poorly to 4-hydroxy-3-methyl-2-butenyl pyrophosphate (HMBPP) stimulation, characterized by the deactivation of these APC markers and impaired proliferation. Furthermore, the adhesion function of γδ T cells, essential for antigen presentation, was greatly reduced in patients with sepsis; for instance, in co-cultures with green fluorescent protein-expressing Escherichia coli, HMBPP-activated γδT cells from healthy individuals adhered to E. coli efficiently, whereas no such phenomenon was observed with respect to γδT cells from patients with sepsis. In line with these results, in co-cultures with isolated CD4(+) αβ T cells, HMBPP-activated γδT cells of healthy individuals promoted the efficient proliferation of CD4(+) αβ T cells, whereas γδT cells from patients with sepsis did not do so. In conclusion, our findings show that the antigen-presenting function of γδT cells is severely impaired in patients with sepsis and the mechanisms behind need further study.