A new SEMA7A variant found in Native Americans with alloantibody

Abstract

Background and objectives: John Milton Hagen (JMH) antigens are carried by Semaphorin 7A that plays important roles in the nervous system and the immune responses. Its role on the erythrocytes is unclear. Over the years, few samples were referred to our Immunohaematology Reference Laboratory to elucidate their JMH status.

Materials and methods: Seven blood samples with antibodies compatible with JMH1-negative red cells were studied at the molecular level to identify polymorphisms and explain the JMH diversity observed. Four samples were of Native American background and three were Caucasians. Molecular analyses of the SEMA7A were undertaken, and soluble form of recombinant Sema7A proteins was produced to characterize the antibodies.

Results: Sequencing of the cDNA showed a polymorphism in SEMA7A exon 9 at position 1040 (G>T) in the four Native American samples. Caucasians had a normal sequence. This polymorphism precludes a change at position 347 where an Arg is replaced by a Leu. Plasma was assayed in ELISA on wild-type Sema7AArg347 and variant Sema7ALeu347 proteins. Results clearly indicated a specific recognition of the antibody produced by the Native Americans for the wild-type Sema7AArg347 protein and not the variant one.

Conclusion: A new SEMA7A variant was identified in this study. The antibody present in the Native American plasma samples should be considered as an alloantibody because it recognizes the wild-type protein.