Oxytocin does not attenuate the ex vivo production of inflammatory cytokines by lipopolysaccharide-activated monocytes and macrophages from healthy male and female donors

Background: Oxytocin (OT) is a neuropeptide shown to attenuate inflammatory responses in both humans and animals, but the specific mechanism underlying these actions has not yet been identified. Preliminary research in humans suggests that monocytes (MOs) and macrophages (MPs) could be the target of anti-inflammatory actions of OT. Here, we present a series of ex vivo experiments in human MOs and MPs, testing whether OT attenuates the cytokine responses of these cells to a common bacterial product, lipopolysaccharide (LPS). Methods: MO experiments were conducted using blood samples taken from healthy volunteers after obtaining informed consent. MPs were purchased frozen from a cell supplier. All samples were cultured under standard conditions: for 6 h at 37°C in a 5% CO₂ atmosphere. A number of variables were considered: volunteer sex, method of MO isolation, LPS concentration, OT concentration, preincubation with OT, cytokines measured, and method of cytokine measurement. Results: Regardless of the specific conditions, no attenuation of LPS-stimulated cytokine production by OT was observed in either MOs or MPs. Conclusion: OT does not attenuate MO or MP inflammatory cytokine production following LPS stimulation. The previously observed anti-inflammatory properties of OT may be attributable to effects on other classes of immune cells or actions in other lymphoid compartments. Alternatively, the effects of OT on inflammation could be secondary to other neurohormonal changes it elicits.