Catalase and lipopolysaccharide enhance proliferation in the rat mixed lymphocyte reaction

Proliferation of rat spleen cells in a mixed lymphocyte culture was amplified fivefold or more in the presence of 2000 units of catalase/ml, as measured by [3H]thymidine incorporation. A similar effect was observed with 1 microgram of lipopolysaccharide (LPS)/ml. Addition of polymyxin B abrogated the promotional effect of LPS, but not that of catalase. These results indicate that the hydrogen peroxide generated by some cells in the rat spleen cell mixed lymphocyte culture suppresses the proliferative response. The demonstration that removal of plastic adherent cells (reducing the percentage of monocytes/macrophages by 75-80%) also results in a 5- to 10-fold increase in a subsequent MLR, indicates that some of the adherent cells may be the producers of hydrogen peroxide, which at higher concentrations suppresses the T-cell proliferation. The enhanced proliferation was not mainly due to increased interleukin 2 (IL-2) production, since the IL-2 concentrations of catalase and LPS-containing cultures were lower than those of control cultures.