Characterisation of gamma delta (γδ) T cell populations in patients with sepsis.

Gamma delta (γδ) T cells contribute to both innate and acquired immune responses during infection. In this pilot study, we measured the in vitro responses of γδT cell populations from patients with sepsis compared to cells from healthy subjects. We also measured production of interferon (IFN)γ. Mononuclear cells were isolated from 10 healthy control subjects and 20 patients with sepsis. Cells were cultured for 7 days with interleukin (IL)-2 plus the bisphosphonate zoledronic acid which results in indirect cell activation. Flow cytometry was used to characterise the γδT cells and enzyme immunoassay was used to measure IFNγ production. The median [range] proportion of γδT cells in healthy controls after activation was 19.2% [2.0-55.9%], compared to only 0.61% [0.1-3.6%] (P < 0.0001) in patients with sepsis. However, IFNγ levels in culture supernatants were similar in both the patients and healthy subjects. We therefore characterised the cells further by CD27 and CD45RA expression in a additional group of patients and found that the population of γδT cells was mainly CD27 negative which characterised these cells as non-proliferating effector cells. Our results suggest predominance of a non-proliferative effector subset of γδT cells in patients with sepsis, which retain functional activity and may contribute towards the host response to inflammation and infection.