Abstract
Marked differences were observed in the sensitizing ability of soluble extracts of histamine sensitizing factor (HSF) from Bordetella pertussis when given by different routes. The intravenous (i.v.) route was some four times more effective than the intraperitoneal and subcutaneous routes. With soluble preparations of HSF, histamine sensitivity appears within 90 min after i.v. injection and demonstrable sensitivity persists for at least 84 days. Within a narrow dose range, there appears to be a direct relationship between amount of HSF given and degree of sensitivity developed. A second injection of HSF or repeated small doses given at various intervals after the first sensitizing dose do not interfere with histamine sensitization. Only doubtful reduction of sensitization was observed when six doses of 10 µg each were given 1, 2, 3, 4, 8 and 16 days after the initial sensitizing dose of SE.