Serum LOXL2 correlated positively to MMP-9 (r = 0.272, P = 0.001), TGF-β1 (r = 0.435, P < 0.001) and ICAM-1 (r = 0.316, P < 0.001) in PID patients (Fig. 2A–C). Here, MMP9 is linked to pelvic inflammatory disease.