Immunogenic and Antigenic Epitopes of Ig. XXV. Monoclonal Antibodies That Differentiate the Mcg+/Mcg- and Oz+/Oz- C Region Isotypes of Human Lambda L Chains

The C region of human lambda L chains is specified by multiple C lambda genes of which three--C lambda 1, C lambda 2, and C lambda 3--encode for the isotypes designated Mcg+, Kern- Oz-, and Kern- Oz+, respectively. The Mcg, Kern, and Oz factors have been characterized by sequence differences involving specific C lambda amino acid residues. They have also been recognized serologically by polyclonal antisera but, with rare exception, these reagents are no longer available. We have obtained two murine anti-human lambda-chain mAb, 14G1 and 14D1, that recognize antigenic determinants specific for the C lambda isotypes Mcg and Oz, respectively. These antisera have been used to classify as Mcg+/Mcg- or Oz+/Oz- monoclonal lambda-chains (Bence Jones proteins) and intact Ig lambda proteins. There was complete concordance between the chemical and serologic assignment of lambda-chains as Mcg+/Mcg- or as Oz+/Oz-; no single protein expressed both isotypes. There was no evident association between the C region isotype Mcg or Oz and the V region subgroup of the protein tested. However, our finding that four of seven amyloid-associated lambda VI Bence Jones proteins were Oz+ suggests a predominant expression of the C lambda 3 gene product among proteins of this uncommon V lambda subgroup.