C4A and Infertility: The anti-sperm LDH-C4 (IgG) levels in 177 infertile patients were tested by ELISA, and 54 subjects were found to be anti–LDH-C4 IgG positive; within the infertile group, the positivity rates among male and female patients were 31.46% and 29.55%, respectively, implying that the presence of anti–LDH-C4 IgG likely indicates immuno-infertility (48).