Plant polyphenolic-protein conjugates activate murine spleen cells and bind to multiple cell surface components

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 congenitally 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 approximately 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 approximately 23 kDa has a pI of 6.0, one band at approximately 25 kDa has a pI of approximately 5.4, and five bands ranging in size from approximately 26 to approximately 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.