PROS1 and rheumatoid arthritis: Therefore, in addition to determining the roles of other IgM-like innate immune proteins such as lung surfactant protein D [1], [2], [43], [50], [51], the complete understanding of IgM-mediated apoptotic particle clearance is essential to effectively treat and control diseases of biological particle accumulation, autoimmunity (e.g., SLE or rheumatoid arthritis), infection and inflammation.