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Substances isolated from natural sources showing a character of endogenous regulators may have a circular meaning. One example is yolkin, which can be useful as a natural therapeutic agent for treating immunological disorders. In the present work we studied the effect of degree of deglycosylation on the biological activity of yolkin polypeptides. For this purpose, yolkin from hen egg yolk was fractionated by gel permeation chromatography (Sephacryl S 100 - HR and Zorbax GF- 250 columns) and enzymatically deglycosylated. The immunoregulatory activity of yolkin fractions (ysec, y4 and y9) were estimated by their induction of proinflammatory factors. The induction of cytokines IL-6, IL-10, and TNF-α in human whole blood cell cultures and nitric oxide from bone-marrow mouse macrophages BMDM were measured. The obtained results showed that all of the yolkin polypeptides, irrespective of size, exerted a strong cytokine and nitric oxide induction, indicating that all of the yolkin constituents possess these activities. The results indicated that the presence of carbohydrate in yolkin polypeptides is unnecessary to preserve cytokine inducing activity and NO generation. Furthermore the removal of carbohydrates from the yolkin by PNGase F led to a significant increase in the level of secretion of nitric oxide from the macrophages. [ABSTRACT FROM AUTHOR]