Studies on the mechanism of complement‐mediated inhibition of antibody binding to HIV gp41

SUMMARY We have previously demonstrated that HIV envelope gp41 binding to specific antibodies decreases after preincubation of fluid‐phase gp41 in normal human serum. This inhibition is proven to be mediated by the classical complement pathway. In this study recombinant gp41 (rgp41) and/or synthetic peptides were preadsorbed to solid phase, and then complement (normal human serum heated human serum, purified Clq/heated Clq) and anti‐gp41 antibodies were added either after each other or simultaneously, and the amounts of bound antibody, and deposited C3b, C4b and Clq were measured. Complement‐dependent inhibition of antibody binding to solid‐phase rgp41 was found, and Clq seems to be at least partially responsible for this phenomenon. Heating of Clq did not affect this process. Higher amounts of anti‐gp41 antibodies significantly and dose‐dependently enhanced C4b and C3b fixation to solid‐phase rgp41. In the case of synthetic peptides corresponding to the immunodominant region of gp41, significant antibody binding to the solid‐phase peptides was also detected, and pretreatment of peptides preadsorbed to solid phase with normal human serum almost totally abolished the antibody binding.