The role of autocrine factors (AF) secreted by cytotoxic IL-2-dependent CTLL-2 cells along with pyruvate in cell defense from oxidative stress was investigated. The addition of conditioned medium (CM) containing pyruvate and AF into CTLL-2 cell cultures increased significantly cell survival under oxidative stress condition. The kinetics of hydrogen peroxide removal from cell cultures under oxidative stress in the case of CM addition has been obtained. The removal of H2O2 mostly by means of its reaction with pyruvate that is contained in CM has been shown at the beginning of oxidative stress (up to 15 min). Pyruvate content in CM was determined as 138 +/- 7 microM. Cell filtration on column with Bio-Gel P-10 was used for removal pyruvate from CM. Three fractions of CM (A, B and C) were obtained as a result of gel filtration. Pyruvate was not detected in any fraction. The fraction A was eluted from column as the first one and contained the largest molecules. Cell survival test showed the fraction B to have the highest ability to protect CTLL-2 cells under oxidative stress. The fraction A supported cell survival to a less degree and fraction C was shown to have no protective ability. The addition of the fraction B to the cell cultures resulted in preservation of significantly higher intracellular ATP level in the cells under oxidative stress than in the control ones. Moreover, AF of the fraction B was shown to react directly with hydrogen peroxide and inactivate it in the absence of cells. AF of the fraction A did not have such properties.