C3 and Stroke: These analyses also showed that RPC-reactive IgG levels were lower in DR patients who used insulin than those who did not (Fig. 5D, p = 0.0152), that serum C3a levels were elevated in DR patients who had renal problems (Fig. 5E, p = 0.0348) and reduced in the sera of the two DR patients who had stroke (Fig. 5F, p = 0.0086).