Activation of NK cells in patients with chronic bone and joint infection due to staphylococci expressing or Not the small colony variant phenotype.
Chronic bone and joint infections (BJI) are devastating diseases. Relapses are frequently observed, as some pathogens, especially
staphylococci, can persist intracellularly by expressing a particular phenotype called small colony variant (SCV). As natural killer
(NK) cells are lymphocytes specialized in the killing of host cells infected by intracellular pathogens, we studied NK cells of patients
with chronic BJI due to staphylococci expressing or not SCVs (10 patients in both groups). Controls were patients infected with
other bacteria without detectable expression of SCVs, and healthy volunteers. NK cell phenotype was evaluated from PBMCs by flow
cytometry. Degranulation capacity was evaluated after stimulation with K562 cellsin vitro. We found that NK cells were activated in
terms of CD69 expression, loss of CD16 and perforin, in all infected patients in comparison with healthy volunteers, independently
of the SCV phenotype. Peripheral NK cells in patients with chronic BJI display signs of recent activation and degranulation in vivo
in response to CD16-mediated signals, regardless of the type of bacteria involved. This could involve a universal capacity of isolates
responsible for chronic BJI to produce undetectable SCVs in vivo, which might be a target of future intervention
