Leptin is a hormone secreted by adipocytes which stimulates inflammatory response, indicating that it is an important link between nutrition and the immune system.

The aim of the study was to evaluate the influence of leptin on the human peripheral blood monocytes to secrete interleukin-1β (IL-1β), interleukin 1 receptor antagonist (IL-1Ra), cachectin (TNFα) and lymphocytes to release interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-10 (IL-10), interferon γ (IFNγ) in vitro.

We evaluated (by ELISA method) the effect of recombinant human leptin (0.5; 5.0; 50.0 and 500.0 ng/ml) on IL-1β, IL-1Ra and TNFα secretion from human peripheral blood monocytes (activated or not by LPS) and Il-2, Il-4, IL-10, IFNγ from from lymphocytes (activated or not by PHA) cultured in vitro during 24 hrs.

Leptin, at the concentration of 500 ng/ml, potentiated the release of TNFα (139.2±37.8 vs 82.8±33.2 pg/ml; p<0.05) from resting and IL-1β (523.5±26.7 vs.407.0±26.7 pg/ml; p<0.05) from LPS activated monocytes and inhibited the secretion of IL-4 from PHA activated lymphocytes (444.5±173.5 vs. 601.6±248.7; p<0.05).

In conclusion, leptin at very high concentration can potentiate the secretion of some proinflammatory cytokines from monocytes and modulate the Th1/Th2 balance by inhibition of Th2 function.