Lupus-derived human monoclonal IgM anti-DNA antibody displays monospecificity, high affinity and private idiotype specificity

A pharmacologically active monoclonal antibody against the human melanocortin-4 receptor: effectiveness after peripheral and central administration

The hypothalamic melanocortin-4 receptor (MC4R) is a constituent of an important pathway regulating food intake and energy expenditure. We produced a monoclonal antibody (mAb) directed against the N-terminal domain of the MC4R and evaluated its potential as a possible therapeutic agent. This mAb (1E8a) showed specific binding to the MC4R in human embryonic kidney 293 cells expressing the human MC4R and blocked the activity of the MC4R under basal conditions and after stimulation with alpha-melanocyte-stimulating hormone (alpha-MSH). The inverse agonist action of Agouti-related protein was significantly enhanced in the presence of mAb 1E8a. After a single intracerebroventricular injection into the third ventricle, mAb 1E8a (1 microg) increased 24-h food intake in rats. After 7 days of continuous intracerebroventricular administration, mAb 1E8a increased food intake, body weight, and fat pad weight and induced hyperglycemia. Because the complete mAb was ineffective after intravenous injection, we produced single-chain variable fragments (scFvs) derived from mAb 1E8a. In pharmacokinetic studies it was demonstrated that these scFvs crossed the blood-brain barrier and reached the hypothalamus. Consequently, the scFv 1E8a increased significantly food intake and body weight in rats after intravenous administration (300 mug/kg). The pharmacological profile of mAb 1E8a and the fact that its scFv was active after peripheral administration suggest that derivatives of anti-MC4R mAbs may be useful in the treatment of patients with anorexia or cachexia.

V gene sequences of lupus-derived human IgM anti-ssDNA antibody: implication for the importance of the location of DNA-binding amino acids

Binding and structural characteristics of human IgMk anti-ssDNA antibody 7B3 were determined. 7B3 was derived from Epstein-Barr virus-transformed peripheral blood B cells of a lupus nephritis patient. Purified 7B3 bound ssDNA from various species, but not dsDNA or structurally unrelated antigens. The relative avidity of 7B3 was high in comparison with IgM anti-DNA antibodies previously described by other investigators. Sequence analysis showed that 7B3 used VH26/D35/JH3 and Humkv328h5/JK1 germline genes, and had a few mutations in the complementarity determining regions (CDRs). No arginine was expressed in the heavy-chain CDR3. However, the putative DNA contact sites, based on the previous crystallographic and computer modeling studies, were occupied by mutated or germline-derived basic and polar amino acids. These results suggest that a minimally mutated IgM anti-ssDNA antibody with a paucity of arginines could display monospecificity and high avidity if DNA-binding amino acids are enriched at the critical DNA contact sites.

Cationic and high affinity serum IgG anti-dsDNA antibodies in active lupus nephritis

To investigate differences between cationic anti-dsDNA antibodies during active and inactive nephritis, low- and high-affinity IgG anti-dsDNA antibodies were prepared from sera of a lupus patient and compared for their binding affinity, spectrotype, and idiotype expression. The ratio of high-affinity to low-affinity anti-DNA antibodies and the relative avidity of the high-affinity anti-DNA antibodies decreased when active nephritis became inactive. Isoelectric focusing showed that cationic anti-dsDNA populations were present predominantly in the high-affinity fraction during active nephritis and in the low-affinity fraction during inactive nephritis. Idiotypic analysis by ELISA and Western blotting showed that the high-affinity cationic anti-DNA antibodies during active nephritis were idiotypically different from their low-affinity counterparts during inactive nephritis. The differences in binding affinity and idiotypy of the cationic anti-dsDNA antibodies suggest that certain serum IgG anti-dsDNA antibodies with both cationic charge and high affinity may be associated with active nephritis.