Complement Regulation in Tears

Abstract

Abstract As previously reported human tears contain factors which inhibit the activation of the complement system. Using a new elisa method, complement activation in human serum was measured by detecting C3, C4 and C5 deposition on solid phase coated immune complexes. Low concentrations of human tears inhibited the classical pathway C3 and C5 deposition. Higher concentrations of tears were capable of inhibiting both the classical and the alternative pathway C3 deposition. C4 deposition was not affected by tears. Characterisation of the anticomplementary factors in human tears by sucrose gradient ultracentrifugation showed that the main inhibitory effect was associated with lactoferrin. Purified lactoferrin was shown to inhibit the classical pathway C3 deposition on coated immune complexes. These findings suggest that lactoferrin may play an anti-inflammatory role in preventing activation of the complement system on the external surface of the eye.