“Leptin deficiency, a reduced leptin signalling and an increased expression of SOCS-3, all reported in obesity, hypertriglyceridemia, insulin resistance and malnutrition, represent risk factors in host immunity.” “Viral infections cause elevated SOCS-3 expression, which inhibits leptin signalling.” It results in immunosuppression by T-regulatory cells and the host defence system fails to manage the aggression of pathogens, inducing infections and diminished vaccine-specific antibody response.[28]. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.