C3 and systemic lupus erythematosus: In addition to the ancestry-related changes, we found that sSIGLEC-1 levels were associated with lower levels of serum complement component 3 (C3) (P = 5.0 × 10− 3; Fig. 4e), but not with other common serological markers of SLE such as C-reactive protein or anti-nuclear autoantibody levels (see Additional file 3).