Anti-Lu9: the finding of the second example after 25 years

The first and only reported example of anti-Lu9 (an antibody directed at a low-incidence antigen in the Lutheran blood group system and allelic to the high-incidence antigen Lu6) was described in 1973 in the serum of a white female, Mrs. Mull. Her serum also contained anti-Lu1 (-Lua), and subsequently, an anti-HLA-B7 (-Bga) was identified. We report the second example of anti-Lu9 in a white male (GR), found 25 years later. The GR serum was reactive in the indirect antiglobulin test with Lu:-1,2,6,9 antibody-screening red blood cells (RBCs) using either a low-ionic-saline additive solution or polyethylene glycol for enhancement. Lu:6,9 RBCs were reactive with the serum when ficin- or EDTA/glycine-acid-treated, but nonreactive when trypsin- or a-chymotrypsin-treated. Six known examples of Lu:9 RBCs were reactive with the GR serum. His serum did not contain anti-Lua, anti-HLA-B7 (-Bga) or antibodies to 34 low-incidence antigens tested. We have identified the second example of anti-Lu9 that was likely stimulated by transfusion. Because only one of 200 donors was found to be Lu:9, our study suggests that the incidence of the Lu9 antigen may be less than originally thought.