C4A and systemic lupus erythematosus: Different studies observed the association of SLE with Human Leukocyte Antigen (HLA) class 2 antigens (HLA-DR2 and DR3) in both white and black ethnicities; as well as with hereditary diseases due to complement deficiency: C1r, C1s, C1, INH, C4, C2, C5, and C8, mainly with C2 lack.