Figure 3.

C3b and C4b cofactor activity of LHR-A domain variants. The indicated CR1 LHR-A domain variants (Fig. 1) were tested in C4b (A) and C3b (B) cofactor activity assays. CSL040 containing LHR-ABC was used as a control/comparator cofactor activity is expressed as the % of intact C4b or C3b alpha-chain relative to un-cleaved C4b or C3b, respectively. Data points show the mean (±SD) C3b/C4b alpha chain (%) for each CR1 variant concentration (nM or pM) tested in combination with a constant Factor I concentration. IC₅₀ values calculated from these data are shown in Table 2. CR1, complement receptor 1; LHR, long homologous repeat.