Serum components influence antibody reactivity to glycan and DNA antigens

We previously generated three types of anti-glycan monoclonal IgM antibodies that react with certain structures on the glycans of glycosphingolipids and glycoproteins. As the nucleotide sequences for the variable regions of these IgM antibodies showed homology with those of anti-DNA antibodies deposited in public databases, we analyzed the reactivity of the anti-glycan IgM antibodies to DNA by ELISA. We found that anti-α2,6-sialyl LacNAc IgM in the supernatant of a hybridoma culture cross-reacted with DNA, and after purification of the IgM by zirconia column chromatography, the highly purified IgM showed increased cross-reactivity to DNA. As most of the contaminating bovine serum proteins in the culture supernatant were removed by the purification process, it is likely that a part of the removed components influences antibody reactivity to DNA. Purified anti-DNA antibodies prepared from lupus model NZB/W F1 and MRL/lpr mouse sera and normal human serum were then analyzed, and similar results showing increased reactivity to DNA were obtained. Furthermore, ELISA using these purified antibodies and various carbohydrate antigens showed that the antigen-binding specificity of these antibodies was altered by the purification process from serum-containing antibody preparations. Our results indicate that mammalian serum contains components that strongly influence antibody reactivity to carbohydrate antigens, including DNA.