title: The influence of different sera on the in vitro immobilisation of Percoll purified Treponema pallidum, Nichols strain.
abstract: OBJECTIVE
  Investigation of sera, especially rabbit serum, in preventing in vitro immobilisation of Percoll purified T. pallidum.
  
  
  METHODS
  The immobilisation of Percoll purified T. pallidum (Nichols) was studied after pre-incubations with basal reduced medium (BRM), heat-inactivated serum of seven different species of animals, heat-inactivated normal human serum (NHS) and rabbit sera containing a different level of antitreponemal antibodies. Also increasing percentages of heat-inactivated normal rabbit serum (NRS) were studied.
  
  
  RESULTS
  The rapid immobilisation of purified treponemes by NHS is delayed by pre-incubation with NRS in a dose-dependent manner. The treponemes from 5-day infections were immobilised significantly more slowly than treponemes from 7- and 8-day infections. Compared with NRS, pre-incubations with a high-titred, low-titred and "autologous" serum resulted in significantly more rapid immobilisation of the treponemes. With most other animal sera resistance to immobilisation was slight compared with that produced by NRS. Immunofluorescent studies revealed that the treponemes were covered with a layer of the human third complement factor (C3b), within an hour of incubation. With two sequential pre-incubations, a delay of the immobilisation was only noted in those test mixtures in which NRS had been present in both preincubations.
  
  
  CONCLUSIONS
  Rabbit serum delays the rapid in vitro immobilisation of Percoll purified treponemes by normal human serum. There was no evidence that this was caused by preventing access of antibodies (in vivo as well as in vitro) to, or preventing the activation of complement on, the treponemal surface. The evidence points to a mechanism in the fluid phase, suggesting participation of a third factor in the immobilisation process, for instance an enzyme, which can be partially inhibited by rabbit serum component(s).
authors.affiliation: Department of Dermatology and Venereology, Erasmus University Rotterdam, The Netherlands.
authors.forename: H J
authors.initials: HJ
authors.lastname: Engelkens
authors.forename: M
authors.initials: M
authors.lastname: Kant
authors.forename: P C
authors.initials: PC
authors.lastname: Onvlee
authors.forename: E
authors.initials: E
authors.lastname: Stolz
authors.forename: J J
authors.initials: JJ
authors.lastname: van der Sluis
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology; D003102:Colloids; D003179:Complement C3b / Q000276:immunology; D006224:Cricetinae; D004285:Dogs; D004306:Dose-Response Relationship, Immunologic; D006168:Guinea Pigs; D006801:Humans; D007106:Immune Sera / Q000502:physiology*; D008297:Male; D051379:Mice; D011205:Povidone; D011817:Rabbits; D051381:Rats; D012822:Silicon Dioxide; D013552:Swine; D013587:Syphilis / Q000276:immunology; D013997:Time Factors; D014209:Treponema Immobilization Test / Q000379:methods*; D014210:Treponema pallidum / Q000502:physiology*
chemical_list: D000907:Antibodies, Bacterial; D003102:Colloids; D007106:Immune Sera; C016039:Percoll; D012822:Silicon Dioxide; D003179:Complement C3b; D011205:Povidone