Maximum opsonization of baker's yeast particles by normal human serum requires C5. Sera from mice genetically lacking C5 are deficient in yeast opsonic activity but can be restored to normal by addition of highly purified human C5. Human, animal, proprietary and soy milks are comparable to human C5 in opsonic reconstitution of C5-deficient mouse serum. This reconstitution by each milk is inhibited by highly purified anti-human C5. Further characterization of the opsonically active principle(s)

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... n milk has been carried out by comparison of bovine milk with human C5 in the following assays: 1) effective molecular titration of hemolytically active C5 in plasma or milk by lysis of EAC14oxy23 cells in the presence of C6-9; 2) generation of chemotactic activities by addition of endotoxin or antigen-antibody complexes; 3) heat stability of opsonic activity; 4) inhibition of opsonic reconstitution by milk or plasma of C5-deficient mouse serum by addition of highly purified anti-C5, anti-C3, or anti-immunoglobulins; and 5) chromatographic separation.