A highly sensitive chemiluminescence immunoassay for the measurement of coagulation factor XIII subunits and their complex in tears.

Blood coagulation factor XIII (FXIII) is a tetramer (A(2)B(2)) consisting of catalytic FXIII-A and carrier/protective FXIII-B subunits. Besides stabilizing fibrin and protecting it from fibrinolysis, FXIII is also involved in wound healing and angiogenesis. The latter functions could be important in body fluids other than blood. In this study highly sensitive chemiluminescent ELISAs were developed to measure low concentrations of FXIII-A, FXIII-B and FXIII-A(2)B(2) antigen levels in tiny volumes of tear. For all three assays the limit of quantitation was below 0.02 microg/L, within laboratory imprecision did not exceed 12% and the recovery was close to 100%. The calibration curves showed an excellent fitting using second order polynomial equation. In non-stimulated tears from 40 healthy volunteers a low, but consistent amount of FXIII-A and FXIII-B (medians: 1.74 microg/L and 5.73 microg/L, respectively) was measured, mostly in free non-complexed form. The respective median values normalized for tear protein concentration were 0.23 microg FXIII-A/g and 0.85 microg FXIII-B/g. There was no gender and age difference and the values showed non-Gaussian distribution. The results prove that FXIII-A and FXIII-B are low concentration components of tear proteome, which in normal conditions might play a role in the repair of corneal micro-injuries. The developed methods provide a tool for monitoring FXIII subunit and complex levels in pathological conditions.