Studies of the physical biochemistry and complement-fixing properties of DNA/anti-DNA immune complexes
Lennek, R.; Baldwin, A.S.; Waller, S.J.; Morley, K.W.; Taylor, R.P.
Journal of Immunology 127(2): 602-608
1981
ISSN/ISBN: 0022-1767 PMID: 6265554 Document Number: 178914
The influence of the DNA MW, the nature of the anti-ds[double-stranded]DNA antibodies and the antibody/DNA ratio on the physical properties of prepared antibody/DNA immune complexes and their ability to fix complement (C) were examined. The sizes of the complexes were studied by isokinetic sucrose gradient ultracentrifugation. The ability of the complexes to fix C was examined by measuring the amount of immune-complexed 3H-dsDNA that bound to red blood cells in a C-mediated reaction. The mode of binding of antibodies to dsDNA (i.e., monogamous vs. a cross-linking mechanism) was determined in a double-label study which ascertained under what conditions the binding of antibody to high MW 14C-dsDNA from phage PM2 could enhance the binding of a smaller 3H-dsDNA fragment as well. Depending upon the dsDNA MW and the nature of the anti-dsDNA antibodies, DNA/anti-DNA immune complexes of predictable sizes and C-fixing properties can be prepared. As the MW of the dsDNA decreases, the maximum size and C-fixing potential of the immune complexes decreases. If the dsDNA is very small (.apprx. 200 base pairs or less) the immune complexes that it forms with the anti-dsDNA antibodies in most human systemic lupus erythematosus sera do not fix C. Double-label studies provide direct evidence that the majority of anti-dsDNA antibodies bind monogamously to dsDNA, although 1 serum was identified that forms soluble, cross-linked antibody/DNA immune complexes.