Human monoclonal IgMs with anti-Mycoplasma pneumoniae antibody activity

We have previously reported that IgM antibodies to Pep13 P1, the major immunogenic peptide of Mycoplasma pneumoniae (MP) P1 cytoadhesin involved in microorganism cytoadherence, is a part of the natural antibody repertoire expressed early in life. Hence, Pep13P1 belongs to the panel of self and non-self antigens recognized by the primitive B cell repertoire. Considering that antibody activity of human monoclonal IgM associated with lymphoproliferative diseases is representative of the immune repertoire, we analyze, in this study, the antibody reactivity to P1 of twenty human monoclonal IgMs. Interestingly, we show that 25% of them are of anti-Pep13P1 specificity: one is a MIgM with reactivity against intermediate filaments, two are MIgMs with anti-MAG specificity and two IgMs with previously unknown antibody activity. Our results indicate that anti-P1 IgM antibodies are parts of the autoreactive than the heteroreactive B cell repertoire and Pep13P1 may have structural similarities with an unknown self antigen as the corresponding physiologic ligand.