Erythrocyte-dependent mitogenic activity of epigallocatechin gallate on mouse splenic B cells

We previously reported that epigallocatechin gallate (EGCg), the main constituent of tea catechins, displays mitogenic effect on mouse splenic B cells. During research into the mechanism(s), it was found that the mitogenic activity of EGCg was dependent on the presence of red blood cells (RBC). When RBC in T cell-depleted spleen cells were removed, EGCg did not enhance the proliferation of B cells and even showed toxic effect at 25-50 micrograms/ml. When mouse, rabbit or sheep RBC as well as RBC-ghosts were added into the cultures, EGCg showed the mitogenic activity at a range of 1-50 micrograms/ml. Thereafter, we preincubated RBC with EGCg at 4 degrees C for various times and then washed the RBC to remove free EGCg in the suspensions. The EGCg-preincubated RBC also enhanced B cell proliferation. As short as ten minutes was sufficient for EGCg to bind to RBC membrane. These results indicate that EGCg first attached to the membrane of RBC and then stimulated B cell proliferation. The above results suggest an important immunoregulatory function of RBC.