ISOLATION AND CHARACTERIZATION OF A MONOCLONAL HUMAN THYROID PEROXIDASE AUTOANTIBODY OF LAMBDA-LIGHT CHAIN TYPE

Thyroid peroxidase (TPO) autoantibodies, a hallmark of human autoimmun e thyroid disease, may have kappa or lambda light chains. Monoclonal h uman TPO autoantibodies with kappa light chains have previously been d eveloped by cloning and expressing ''combinatorial'' libraries of immu noglobulin genes in bacteria. In the present study, an IgG1/lambda com binatorial library was generated from thyroid cDNA of a Graves' patien t whose serum contained lambda TPO antibodies. Screening the bacteriop hage library with I-125-TPO yielded one clone, TR1.41. The oligonucleo tide sequence of TR1.41 was determined and the nature of its interacti on with TPO was investigated. The affinity of TR1.41 for TPO is high ( K-d similar to 10(-9) M), comparable to that of monoclonal kappa TPO a utoantibodies derived from the same patient. The genes encoding the he avy and light chains of TR1.41 differ in a number of respects from the closest available germline genes. Such differences are consistent wit h somatic mutation in a high-affinity antibody. An important character istic of TR1.41 is its interaction with the immunodominant domain on T PO recognized by similar to 80% of serum TPO autoantibodies. The frequ ency of TPO-specific F(ab) generated from the thyroid gland of patient TR was much lower for F(ab) with lambda light chains (1:150 000) than for F(ab) with kappa light chains (1:13 000). Despite this low freque ncy, the high affinity of TR1.41 and its recognition of the immunodomi nant region on TPO indicate that lambda autoantibodies of this type ma y represent an important constituent of the TPO autoantibody response in man. In conclusion, this is the first report on the molecular cloni ng and characterization of a thyroid autoantibody of lambda L chain ty pe by the combinatorial library approach.