C1S and systemic lupus erythematosus: They concluded that in the majority of SLE cases C1q, C1r and C1s presented a good correlation but also low C1q levels coexisted with high levels of C1s and C1r.24 Furthermore, in patients with lymphopenic hypogammaglobulinaemia the levels of C1s were normal, whereas C1q levels remained unusually low.25 All these data suggest that C1q and C1s are differently regulated in (auto)immune pathologies.