C4A and systemic lupus erythematosus: Several studies have demonstrated that the serum level of the efferocytosis bridging molecule Gas6 is significantly elevated in SLE patients, which is associated with neurological involvement, plasmacytosis, renal dysfunction, high dsDNA antibody titers, and decreased levels of complement C3 and C4 (38), which is probably due to the targeting of the MerTK (17).