Pro-inflammatory cytokines of a T helper-1-signature are known to promote insulin resistance (IR) in obesity， but the physiological role of this mechanism is unclear. It is also unknown whether and how viral infection induces loss of glycemic control in subjects at risk for developing diabetes mellitus type 2 (DM2). We have found in mice and humans that viral infection caused short-term systemic IR. Virally-induced interferon-γ (IFN-γ) directly targeted skeletal muscle to downregulate the insulin receptor but did not cause loss of glycemic control because of a compensatory increase of insulin production. Hyperinsulinemia enhanced antiviral immunity through direct stimulation of CD8 effector T?cell function. In pre-diabetic mice with hepatic IR caused by diet-induced obesity， infection resulted in loss of glycemic control. Thus， upon pathogen encounter， the immune system transiently reduces insulin sensitivity of skeletal muscle to induce hyperinsulinemia and promote antiviral immunity， which derails to glucose intolerance in pre-diabetic obese subjects. VIDEO ABSTRACT.