CDR3 REGIONS IN THE PREIMMUNE V-H B-CELL REPERTOIRE OF LPR MICE

Previous studies have suggested that the CDR3 genetic element of the h eavy chain variable region of autoantibodies is important in determini ng reactivity against self antigens, particularly against DNA. The lpr mutation was recently found to encode for a defective form of the fas protein, a molecule important for the transmission of the apoptotic s ignal into cells. Our aim was to determine whether CDR3 elements simil ar to those described for autoantibody-producing hybridomas derived fr om lupus-prone strains could be found in the preimmune repertoire of B cells in mice with the lpr mutation. The analysis of the junctions of the V-H-C-mu functional rearrangements derived by polymerase chain re action (PCR) amplification of RNA obtained from splenic small, resting cells stimulated with lipopolysaccharide (LPS) from male lpr mice sho wed that a large proportion of them expressed D genes in the unusual r eading frames 2 and 3. Two of the lpr joints were formed by D-D fusion s. Similarly, nearly half of the lpr sequences had arginines, an amino acid which promotes binding to dsDNA and is seldom observed in normal junctions. Our results show that the preimmune repertoire of lpr anim als has abnormal CDR3 elements which may result from a failure at diff erent levels of selection. The antigen-dependent selection of such ele ments that leads to the expansion of specific, high-affinity anti-dsDN A antibody-producing clones might depend on other genetic factors not found in the C57B1/6-lpr strains but in the MRL-lpr.