Plant Polyphenolic-Protein Conjugates Activate Murine Spleen Cells and Bind to Multiple Cell Surface Components

Abstract

Abstract

Previous studies have shown that a flavonoid-phenolic-rich glycoprotein (TGP) is a mitogen to murine B cells. To test the hypothesis that this could be duplicated by a protein conjugate of the phenolic moiety, the response to rutin (R)-BSA was studied. It was demonstrated that: (i) R-BSA, like TGP, activates mouse B cells to proliferate; (ii) the kinetics of proliferation induced by R-BSA and TGP are similar; (iii) the mitogenic effects of neither R-BSA nor TGP are inhibitable by free flavonoids or phenolics; (iv) there is no age-dependent decrease in the proliferative response to either R-BSA or TGP; (v) both R-BSA and TGP induce spleen cells to secrete IL-6 by 2 hr of culture. They differ in that the proliferative response of congenially athymic mice to R-BSA, but not to TGP, is significantly lower than that of euthymic mice, and in that TGP seems to stimulate a small subpopulation of T cells to enter cell cycle.

The importance of the phenolic moiety in the response to TGP is supported by the observation that R-BSA immunoprecipitates cell surface components that seem to be identical to those precipitated by TGP. The apparent molecular sizes of the bands are ~110, 70, 55, 43, 34, 29, and 25-23 kDa. The 2-D analyses of the TGP and R-BSA precipitates are also striking in their similarity. The isoelectric point (pi) of the 28-kDa band is between pH 6.3 to 6.6. A band at ~23 kDa has a pi of 6.0, one band at −25 kDa has a pi of −5.4, and five bands ranging in size from ~26 to ~110 kDa all have a pi in the pH range of 4.6 to 5.4. The presence of multiple binding sites suggests that these compounds might activate cells via multiple distinct pathways.