Complement in tears from normal humans.

Tears from ten normal persons were used in hemolytic assays to test for activity of total hemolytic complement (tested in all ten subjects), activities of each of the nine complement components (tested in two subjects), and activity of the alternate pathway (tested in two subjects). A modified radial-immunodiffusion method was used to confirm the presence of C3 and C4 complement proteins in the tear samples from all ten subjects. Factor B protein was detected in tears from two of four normal subjects tested. In dilutions up to 1:4, hemolytic activity was observed in tears from five of the ten subjects. Samples from the remaining five subjects had CH50 activity at dilutions up to 1:2. In control tests, human serum had CH50 activity at 1:32. No lysis occurred in Veronal-buffered saline or in serum and tears heated to 56 degrees C for 30 minutes. Complement proteins C3 through C9 displayed hemolytic activity in tears from each of two subjects tested for complement components. The classic and alternate complement pathways in tears can be included among the defense mechanisms of the ocular surfaces.