Naturally-occurring anti-Jka in infant twins.

Anti-Jka was detected by solid-phase red cell adherence (SPRCA) antibody detection and identification tests in the plasma of a 9-month-old female infant during a routine presurgical evaluation. The patient and her nonidentical twin sister, who also had anti-Jka in her plasma, were products of an uncomplicated in vitro fertilization, full-term pregnancy, and vaginal delivery. Neither twin had been transfused, recently infected, or treated with medication. Their mother had no prior pregnancies or transfusions. Red blood cells (RBCs) from the patient and her sister typed as Jk(a-b+) by direct hemagglutination, and this phenotype was confirmed by negative adsorption and elution studies. Both infants' plasma samples were strongly reactive with 20 examples of Jk(a+) RBCs and nonreactive with 20 examples of Jk(a-) RBCs by SPRCA assays. Anti-Jka was not detected in either twins' plasma by indirect antiglobulin tests by tube method in low-ionic- strength saline solution or polyethylene glycol, or with ficin- or papain-treated RBCs. Monocyte monolayer assays using Jk(a+) RBCs sensitized by either twins' serum were nonreactive (0%). RBCs from both parents typed as Jk(a+b+). Both parents' antibody detection test results by SPRCA assay were negative. The absence of a history of exposure to allogeneic RBCs or possible passive transfer of maternal or other alloantibody classifies these antibodies as naturally-occurring anti-Jka.