Further characterization of a factor from endotoxin-treated serum which releases histamine and heparin from mast cells.

Upon incubation of hamster serum with bacterial endotoxin, a factor is produced which releases histamine and heparin from hamster mast cells and increases capillary permeability in guinea pig skin. The major histamine-releasing activity derived from hamster serum was characterized by gel filtration, found to have a molecular weight of approximately 60,000, and shown by electrophoresis to migrate with alpha-2- or beta-1-globulins. The ability to increase vascular permeability was not reversed by antihistamine. On the basis of these properties, the histamine-liberating factor generated by endotoxin in hamster serum differed significantly from known anaphylatoxins.