C3 and obstructive sleep apnea syndrome: The serum IgA ((1.63 ± 0.09) g/l vs. (1.03 ± 0.12) g/l) and C3 levels ((1.17 ± 0.11) g/l vs. (0.83 ± 0.12) g/l) of the OSAHS group significantly exceeded those of the control group (P<0.05), but their IgG ((10.63 ± 0.89) g/l vs. (10.43 ± 0.91) g/l), IgM ((1.22 ± 0.11) g/l vs. (1.32 ± 0.13) gl) and C4 levels ((0.23 ± 0.02) g/l vs. (0.18 ± 0.02) g/l) were similar (P>0.05) (Fig.3).