The mechanism of non-immune inhibition of biological activity of IL-2 by IgG or its immune complexes was studied using serological analysis on the model of IL-2-dependent proliferation of Con A-induced blast cells obtained from a mouse spleen. The mechanism investigated is realized through formation of a complex between IL-2 and an effector part of IgG molecule. It is suggested that this mechanism can participate in immune regulation, formation of individual and population resistance to infections, and pathogenesis of infectious and non-infectious diseases with antigen persistence.