Anti-DNA antibodies. Their idiotypes and SLE

Affinity maturation of an antibody for the UV-induced DNA lesions 6,4 pyrimidine-pyrimidones

DNA lesions, associated mostly with minor changes in DNA structure, may induce permanent change in heritable coding information. Biochemically, these minor structural changes are difficult to be explored for generating high-affinity antibodies to detect specific DNA lesions in varying sequence contexts. Herein, we established a platform of bacterial display to facilitate antibodies to be matured with high affinity and high specificity against DNA lesions. To achieve this goal, we, for the first time, developed a two-round mutation/screening strategy: (1) using multiple lesion-containing DNA probes for primary maturation and (2) using single lesion-containing DNA probes for second maturation. Specifically, we capitalized on 64M-2 as a parental template to improve affinity for 6-4PP by 710-fold, compared with the model one. In addition, the matured antibody (9c3) is found to be much less dependent on the bases surrounding 6-4PPs than the model one. The mechanistic study from both computational simulation and reverse mutations revealed the critical roles of the two-round mutations in the enhanced binding affinity and independence of surrounding bases. This selection strategy opens a new way to improve affinity and specificity of antibodies for other DNA lesions.

Idiotype usage by polyclonally activated B cells in experimental autoimmunity and infection

Both in animal models and in human systemic lupus erythematosus (SLE) the occurrence of nephritogenic autoantibodies bearing dominant idiotypes has been described. In this study we investigate the relation between the induction pathway of polyclonal B cell activation and the production and glomerular deposition of nephritogenic antibodies with shared dominant idiotype(s). Polyclonal B cell activation was induced in several experimental models characterized by glomerular immune deposit formation. We monitored the occurrence of dominant idiotypes among immunoglobulins deposited in the glomeruli. In addition, we studied the species specificity of the dominant idiotypes, by monitoring their presence in kidney sections of patients with an immunologically mediated kidney disease. Anti-idiotype antisera against two monoclonal anti-DNA autoantibodies were used, derived from MRL-lpr/lpr mice, i. e. clone H241 and clone H130. Autoantibodies with the H241 idiotype were present in immune complex depositions in all experimental models but not in humans. We therefore conclude that the presence of this dominant idiotype is independent of the induction pathway of polyclonal B cell activation. However, autoantibodies bearing the H130 idiotype were only detected in kidney sections of mice with spontaneous lupus.