CD40LG and Parkinson disease: Male PD patients had remarkably lower levels of IgM, C3, and C4 than male healthy controls [0.93 (0.44) vs. 1.14 (0.75), p = 0.025; 0.87 (0.22) vs. 0.96 (0.19), p = 0.001; 0.19 (0.06) vs. 0.22 (0.07), p = 5.89E-6; respectively] (Supplementary Table 1).