Molecular characterization of a human monoclonal antibody to B antigen in ABO blood type.

A human anti-B antibody of clone BT97 was obtained from a healthy individual of type A of the ABO blood group without immunization. Cloning was performed by means of heterohybridoma formation of cell fusion between human peripheral lymphocytes and mouse myeloma cells. The antibody selectively reacted with B-antigen in flow cytometry using red blood cells and enzyme-linked immunosorbent assay. The VH and VL genes of BT97 were derived from the germline genes of DP-47 and 3p.81A4, respectively, with a couple of somatic mutational events. Comparative analysis with other reported anti-A, B and H antibodies revealed that the amino acid sequence of the VH region was more homologous than that of the VL region. The sequence of BT97 showed complete identity with one anti-H natural antibody reported by Marks et al., with the exception of the CDR3 region. It is not known whether the homologies include the common properties of the natural antibodies; however, a particular germline gene potentially changes to anti-ABH antibodies. We think that this method is suitable for cDNA preparation of human monoclonal antibodies to blood group antigens and for sequence analysis.