Retinoid metabolism in human leucocytes.

Leucocytes from subjects from 0 to 80 years old were separated into mononuclear and granulocyte fractions and the retinoids and retinoid-binding fractions were examined. Both leucocyte fractions were found to contain retinol, retinoic acid and an additional retinoid; retinoic acid comprised 40% of retinoids in some samples. The protein fractions containing retinoids included a 200 kDa protein and several 14-18 kDa proteins. Plasma concentrations of retinol changed little with increasing age. In contrast, leucocyte concentrations of retinoids and retinoid-binding proteins increased quadratically with age. However, in granulocytes from young children retinoids were almost undetectable.