CHOLERA-TOXIN STIMULATES HUMAN B-CELL DR ANTIGEN BIOSYNTHESIS AT THE LEVEL OF TRANSLATION

Cholera toxin (CT) exerts many diverse regulatory effects on cells of the immune system and is considered a potent adjuvant on gut mucosal i mmune responses to orally presented antigens. It has been previously d escribed that CT induces surface DR expression in human resting B-cell s. As a further step toward understanding this phenomenon, the molecul ar mechanisms underlying the regulation of DR expression were investig ated. By the use of Western analysis, it is shown that CT increases th e total levels of DR protein in highly purified human tonsillar cells. [S-35]Methionine incorporation studies show that the aforementioned i ncrease is due to de novo biosynthesis of DR protein at as early as 6 hr after CT stimulation and is completed by 24 hr. [H-3]Uridine uptake experiments, nuclear transcription runoff assays, and Northern analys is show that CT does not exert its effect at a transcriptional level, indicating translational regulation. Anti-IgM, which mimics B-cell ant igen binding, behaves in a manner similar to CT. The B subunit of CT ( B-CT) and prostaglandin E-2, either alone or in combination, do not in duce DR protein biosynthesis nor do they exert any effect on the trans cription of DR beta 1 gene. These results show that cAMP elevation as well as binding of B-CT to GM-1 ganglioside, by themselves, do not lea d to DR protein biosynthesis suggesting that other activation pathways may be involved. (C) 1997 Academic Press.