Rapid detection of JMH antibodies with recombinant Sema7A (CD108) protein and the particle gel immunoassay.

BACKGROUND: At present, identification of antibodies against the high-prevalence JMH antigen is difficult and limited to reference laboratories having panels of rare red blood cell (RBC) specimens in stock. Here, a novel method is described for detection of anti-JMH with particles coated with recombinant semaphorin 7A (Sema7A, CD108), the protein that carries the JMH blood group antigens. STUDY DESIGN AND METHODS: Recombinant Sema7A protein was generated and coupled onto superparamagnetic particles coated with streptavidin. The coated particles were tested in the presence of different serum and plasma samples (11 anti-JMH, 20 other antibodies, and 50 samples from nonimmunized blood donors) with the particle gel immunoassay and flow cytometry. RESULTS: Sema7A-coated particles reacted with all 11 samples containing anti-JMH, but not with samples lacking anti-JMH. In addition, the anti-JMH agglutination scores were higher with Sema7A-coated particles than with JMH-positive RBCs in all cases. CONCLUSION: Recombinant blood group proteins have the potential to replace RBCs as antigen carriers for identification of certain RBC alloantibodies.