The heavy (H) and light (L) chain V-region sequences of eight human autoreactive immunoglobulin M (IgM) monoclonal antibodies (mAbs: BY-4, BY-7, BY-12, IRM-3. IRM-7, IRM-8, IRM-10 and CDC-1) were determined at the cDNA level. All V-H and V-L families were identified. Four different VH families were represented, V(H)3 being the most common as five of the mAbs (BY-7, BY-12, IRM-3, IRM-8 and CDC-1) used genetic elements of this family, whereas V(H)1, V(H)2 and V(H)4 were only present in IRM-7, BY-4 and IRM-IO, respectively. BY-4, BY-7, BY-12, IRM-7 and IRM-10 reacted with a variety of self as well as non-self antigens, thus exhibiting polyreactive behaviour. Comparison of the gene segments utilized by these mAbs with their germline counterparts revealed that the gene segments were close to germline configuration. The length of H-CDR3 was found to be relatively long (27-60 nucleotides) among the polyreactive mAbs and the presence of Tyr and Trp residues in this region seems to be of vital importance for polyreactivity. We have analysed the utilization of gene elements and the presence of amino acid residues in regions particularly important for antigen binding, such as CDR. Common molecular features relating to the function of the mAbs are discussed.
