C3 and pulmonary arterial hypertension: Moreover, the CH50 results from rat plasma samples of the PAH experiment groups stand in line with our hypothesis, MCT group has the highest average CH50 value, indicating obvious C3 activation, while CP40-KK treatment could reverse it, which means CP40-KK worked in vivo in rats as well (Fig. 2D). Tail bleeding time after 2 weeks of CP40KK treatment in different groups were also analyzed, CP40KK could significantly prolong the tail bleeding time in the rats (Fig. 2E).