Mice and rats which are normally resistant to histamine become more susceptible to its lethal action after an injection of H. pertussis. This so-called sensitization to histamine is not an anaphylactic phenomenon. It is due to the action of a component of H. pertussis, the histamine-sensitizing factor (HSF), which in some unknown way overcomes the physiological mechanism in rats and mice that makes them more resistant than other species to histamine. Guinea-pigs which appear not to possess this mechanism and are about 200-fold more susceptible, weight for weight, than rats and mice, were not made more sensitive by H. pertussis.
After a stated dose of vaccine, sensitization was detectable in 48 hr., reached a maximum in 3–4 days, remained at this level for about 2 weeks and gradually disappeared. The effects of dosage, route of injection, and weight and sex of mice have been examined.
The HSF was found in strains of H. pertussis; it was not found in H. parapertussis, H. bronchisepticus or H. influenzae. It was only slightly affected by heating at 70° C. for 1 hr. but was destroyed at 80° C. in ½ hr. It was destroyed when bacteria were disintegrated by shaking with glass beads, or by grinding after being freeze-dried. It was found in the supernatant fluid of a partially autolysed vaccine.
HSF was antigenic. Antisera were prepared in rabbits. Anti-HSF combined with HSF and neutralized its histamine-sensitizing activity. Bacteria treated with antiserum in vitro absorbed anti-HSF and did not thereafter sensitize mice.
Antiserum protected mice passively against the sensitizing action of vaccine, presumably by combining with HSF. After sensitization had developed the sensitive state was not affected by antiserum.
Although HSF is an antigen there was no indication that histamine-sensitization was due to its antigenicity.
The HSF was differentiated from heat-labile and heat-stable toxin, haemagglutinin, capsular material and agglutinogen.
The preparation V 17, which is a small fraction of the disintegrated bacteria, adsorbed on red cell stromata (Pillemer et al. 1954) had a high histamine-sensitizing value. Compared with whole bacterial vaccine it caused little production of agglutinin in mice; in rabbits it caused a slower and smaller production of agglutinin and a faster and greater production of anti-HSF. For this reason immune rabbit sera may have a high agglutinin titre and a low anti-HSF value or vice versa. Anti-HSF rabbit serum protected mice against sensitization by V 17.
Vaccines could be graded according to their histamine-sensitizing activity. This did not always correspond to their grading by agglutinin production in mice. The relation of HSF to the immunizing antigen of H. pertussis and the use of histamine-sensitization to indicate the immunizing potency of pertussis vaccines are discussed.
We wish to thank Glaxo Laboratories Ltd. for the supply of reference vaccine, and the Whooping Cough Immunization Committee of the Medical Research Council for vaccines and sera.