Two human neonatal IgM antibodies encoded by different variable-region genes bind the same linear peptide: Evidence for a stereotyped repertoire of epitope recognition

Two monoclonal IgM Abs have been produced from lymphocytes isolated from tw o human umbilical cord bloods, These mAbs recognize a conformational epitop e present in a CNBr digestion fraction of lactoferrin, Linear epitopes reco gnized by each mAb were selected from several phage display peptide librari es. In each case, phages displaying a peptide with a moth defined by [WF],G ,[EQS],N were recovered. Phages displaying that moth bound equally well to either mAb but did not bind to control IgM, A peptide bearing this moth com peted with the phage-displayed peptides for binding to either mAb, The same peptide also competes with a component of the CNBr digestion fraction of l actoferrin for Ab binding in ELISA. The Abs use different families of V-H, J(H), and V-K gene cassettes but use the same J(K) cassette. All segments a re virtually identical to their germline gene counterparts. This work provi des further evidence that certain innate specificities are stereotyped amon g individuals.