CD91 plays an important role in the scavenging of apoptotic material, possibly through binding to soluble pattern-recognition molecules. In this study, we investigated the interaction of CD91 with mannan-binding lectin (MBL), ficolins and lung surfactant proteins. Both MBL and L-ficolin were found to bind CD91. The MBL-CD91 interaction was time- and concentration-dependent and could be inhibited by known ligands of CD91. MBL-associated serine protease 3 (MASP-3) also inhibited binding between MBL and CD91, suggesting that the site of interaction is located at or near the MASP-MBL interaction site. This was confirmed by using MBL mutants deficient for MASP binding that were unable to interact with CD91. These findings demonstrate that MBL and L-ficolin interact with CD91, strongly suggesting that they have the potential to function as soluble recognition molecules for scavenging microbial and apoptotic material by CD91. Structured digital abstract • MINT-8040679, MINT-8040706: MBL (uniprotkb: P11226) binds (MI:0407) to CD91 (uniprotkb: Q07954) by enzyme linked immunosorbent assay (MI:0411) • MINT-8040690: L-ficolin (uniprotkb: Q15485) binds (MI:0407) to CD91 (uniprotkb: Q07954) by enzyme linked immunosorbent assay (MI:0411) • MINT-8040663: C1q B (uniprotkb: P02746), C1q C (uniprotkb: P02747), C1q A (uniprotkb: P02745) and CD91 (uniprotkb: Q07954) physically interact (MI:0915) by enzyme linked immunosorbent assay (MI:0411) • MINT-8040821, MINT-8040869, MINT-8040928: CD91 (uniprotkb: Q07954) binds (MI:0407) to MBL (uniprotkb: P11226) by surface plasmon resonance (MI:0107) • MINT-8040880: CD91 (uniprotkb: Q07954) binds (MI:0407) to L-ficolin (uniprotkb: Q15485) by surface plasmon resonance (MI:0107)
