An apparent anti-Jka reacting only in the presence of methyl esters of hydroxybenzoic acid.

An apparent anti-Jka, reacting only in the presence of methyl esters of hydroxybenzoic acid (HBA), was detected in an individual with Jk (a+) red blood cells. The antibody was first detected when a commercial low-ionic-strength-solution preparation containing the preservative methyl paraben (a methyl ester of hydroxybenzoic acid) was used in compatibility testing. Negative reactions were obtained when regular saline, albumin, and enzyme technics were employed. The positive indirect antiglobulin tests were due to cell-bound complement; no IgG was detected. The patient had no clinical or hematologic evidence of hemolytic anemia and was transfused with Jk(a+) red blood cells with no ill effects. It is postulated that immune complexes formed between the antibody and the chemical may result in a site complementary to some aspect of the Jka antigen. When this complex binds to Jk(a+) cells, complement is activated and some complement components remain on the cells. We do not know why only Jk(a+) cells were involved in these reactions.