Immunological characterization of riboflavin carrier proteins using monoclonal antibodies

Monoclonal antibodies to chicken riboflavin carrier protein have been produced by fusing immunized mouse spleen cells with myeloma SP2/O-Ag 14. The three different monoclonal antibodies specifically bound 125I-labelled chicken riboflavin carrier protein and were characterized with respect to their affinities to bind the antigen, subclass and isotype. These three monoclonal antibodies had similar affinities for holo-, apo- and SDS-denatured riboflavin carrier protein but were unable to recognize the reduced and carboxymethylated protein indicating that they were directed to specific conformational epitopes on the native avian protein. Succinylation of the vitamin carrier protein while still retaining flavin binding characteristics totally abolished the cross-reactivity with all the three monoclonal antibodies indicating that lysine residues were involved at the antigenic sites of the protein. This shows that the antigenic loci may be distinct from the flavin binding sites in the protein. All three antibodies were able to recognize riboflavin carrier protein present in the sera of pregnant rats, monkeys and humans indicating that the epitopes to which they are directed are conserved throughout evolution. These antibodies can therefore be effectively used for radioimmunoassays and further studies on the functional aspects of this protein in higher mammals