The action of formaldehyde on staphylococcal δ haemolysin (Plate XIV)

Native staphylococcal δ haemolysin was poorly immunogenic in the mouse. After treatment with formaldehyde at pH 5 or pH 7·5, haemolytic activity was rapidly lost but antigenic reactivity retained and, at pH 5, im-munogenicity was enhanced. Treatment of the haemolysin with formaldehyde at pH 9·5 reduced haemolytic activity by 97% but did not enhance immunogenicity. There was no evidence of polymerisation of formaldehyde-treated δ haemolysin, and the enhanced immunogenicity was considered to be partly due to a reduced affinity for phospholipids.