Structural study of clones isolated from a human lens epithelial cell cDNA library with human antibody probes from a patient with cataract

Purpose: Previous work demonstrated that serum antibodies (JgG and IgM) from cataract patients killed lens epithelial cells (LECs) in culture. The goal of this study is to identify the lens antigens (Ag) to which these antibodies (Ab) are directed. Methods: A cDNA library constructed from mRNAs of 100 human capsulotomy specimens containing LECs was screened with human sera from cataract patients. The sequences of these cDNAs were determined. The proteins encoding by these clones were expressed in E. coli. Abs were raised by immunization with partially purified protein expressed in E. coli emulsified with CFA in mice. Tissue specificity of these proteins was studied by immunohistochemistry. The cidal potency of Abs on LECs in culture was confirmed by the trypan blue exclusion test. Results: We have obtained more than 20 different individual cDNA clones. The entire DNA sequences of two clones encoding a 48-kDa-protein and MP70 were determined and protein sequences were deduced. No sequence homology was found between 48-kDa-protein and any known proteins in the data bank. MP70 in human LECs has the highest sequence homology with mouse connecxin (MP70). Immunocytochemistry with antibody probes and northern blots with cDNA probes indicated that these proteins are predominantly expressed in lens cells. The Abs against MP70 or 48-kDa-protein killed mouse LECs in culture. Conclusions: Sera from cataract patients contain auto-Abs against 48-kDa-protein and MP-70 and these Abs killed LECs.