Viable Coxiella burnetii induces differential cytokine responses in chronic Q fever patients compared to heat-killed Coxiella burnetii

Abstract

Cytokine responses of chronic Q fever patients to the intracellular bacterium Coxiella burnetii have mostly been studied using ex-vivo stimulation of immune cells with heat-killed C. burnetii due to the extensive measures needed to work with viable BioSafety Level 3 agents. Whether research with heat-killed C. burnetii can be translated to immune responses to viable C. burnetii is imperative for the interpretation of previous and future studies with heat-killed C. burnetii Peripheral blood mononuclear cells (PBMCs) of chronic Q fever patients (n=10) and healthy controls (n=10) were stimulated with heat-killed or viable C. burnetii of two strains, Nine Mile and the Dutch outbreak strain 3262 for 24 hours, 48 hours and 7 days, in the absence or presence of serum containing anti-C. burnetii antibodies. When stimulated with viable C. burnetii, PBMCs of chronic Q fever patients and controls produced less pro-inflammatory cytokines (IL-6, TNFα, IL-1β) after 24 hours compared to stimulation with heat-killed C. burnetii. In the presence of Q fever seronegative serum, IL-10 production was higher after stimulation with viable as compared to heat-killed C. burnetii, however when incubating with anti-C. burnetii antibodies serum, the effect on IL-10 production was reduced. Adaptive, merely T-cell derived, cytokine (IFNγ, IL-17, IL-22) and CXCL9 production were not different between heat-killed and viable C. burnetii stimulatory conditions. Results of previous and future research with heat-killed C. burnetii should be interpreted with caution for innate cytokines, but heat-killed C. burnetii-induced adaptive cytokine production is representative of stimulation with viable bacteria.