Disease due to infection is the result of interaction between a microorganism and the defence mechanisms of the body. The outcome of this interaction can range from no demonstrable effect to death, and will depend on the number and virulence of the organisms, the physiological and anatomical effects that they induce, and the effectiveness of the body's natural defences. There are strong genetic influences which determine the response to infection. Clear examples of this are the genetic polymorphisms in expression of cytokine release (e.g. tumour necrosis factor-alpha, TNF-α) and cytokine receptor expression (e.g. interferon-gamma, IFN-γ).