C4A and systemic lupus erythematosus: On the other hand, the mean copy numbers of C4A (1.82 ± 0.93 in SLE, 2.08 ± 0.93 in controls; p < 0.001) and C4B (1.96 ± 0.93 in SLE and 1.81 ± 0.72 in controls; p < 0.001) were both significantly reduced in SLE.