CIRCULATING ANTI-(XANTHINE OXIDOREDUCTASE) ANTIBODIES IN HEALTHY-HUMAN ADULTS

Levels of free anti-(xanthine oxidoreductase) (XOR) antibodies in the serum of normal healthy human subjects were determined, using both hum an and bovine enzyme as antigen, in an enzyme-linked immunosorbent ass ay (ELISA). Levels of IgM class anti-(human XOR) antibodies were found to be particularly high (mean values representing approximately 3% of total IgM) and to be significantly higher than levels of IgM anti(bov ine XOR) antibodies, indicating that endogenous XOR, rather than inges ted bovine milk XOR, is the immunogen. IgM anti-XOR antibody levels we re significantly higher in women under 50 years than in age-matched me n, or in older women. Levels of IgG class anti-XOR antibodies were muc h lower and showed no correlation with gender or age. Affinity-purifie d anti-(human XOR) antibodies only partially inhibited enzymic activit ies of XOR. The majority of both IgM and IgG anti-(human XOR) antibodi es in serum occurred as immune complexes, suggesting that the specific antibodies have a protective role in removing potentially damaging XO R from the circulation.