Additionally, since there are close relationships between DAPs (C1s, C3, C5, C6, C9 and Kng1) and their receptors (C5AR1, C3AR1, CR2 and B2R) [12,13], an action mechanism of amygdalin on rheumatoid arthritis was tentatively proposed in Figure 7. Here, CR2 is linked to rheumatoid arthritis.