The influence of complement receptor type 1 (CD35) and decay-accelerating factor (CD55) on complement receptor type 2-(CD21) mediated alternative pathway activation by B cells

The influence of complement receptor type 1 (CR1; CD35) and decay-accelerat ing Factor (DAF; CD55), both down-regulators of complement activation, on t he complement receptor type 2-(CR2) mediated alternative pathway (AP) activ ation of complement on normal B cells, was assessed. The data indicate that , while neither DAF nor CRI hinder the function of the AP convertase formed on CR2, CR1 plays a significant role in the remodelling of C3b fragments, generated by the convertase and deposited at secondary acceptor sites on th e B-cell surface, such that they become suitable ligands for CR2. The signi ficance of this finding is briefly discussed.