Treponemicidal antibody measured by the "washed-killing" assay correlates with immunity in experimental rabbit syphilis.
OBJECTIVE
The authors have previously shown that complement-dependent treponemicidal antibody measured by the "washed-killing" assay is directed exclusively against surface-exposed targets on Treponema pallidum, presumably the Treponema pallidum rare outer membrane proteins detected by freeze-fracture electron microscopy.


OBJECTIVE
Because immune mechanisms against Treponema pallidum rare outer membrane proteins are likely to be central to a protective host response, it was examined whether a relationship could be established between treponemicidal levels as measured by the "washed-killing" assay and host immunity in experimental syphilis.


METHODS
Three groups of Treponema pallidum-infected rabbits were treated curatively with penicillin at 9 days, 30 days, and 6 months post-infection to generate animals with varying degrees of immunity to challenge re-infection. The level of complement-dependent treponemicidal activity in sera obtained before infection (basal) and before intradermal challenge was determined by the "washed-killing" assay and compared with that detected using conventional in vitro immobilization.


RESULTS
Using the "washed-killing" assay, a close quantitative correlation as measured by a treponemal immobilizing endpoint titer was demonstrable between prechallenge treponemicidal antibody and the status of immunity to re-infection. Sera from rabbits completely susceptible to symptomatic and disseminated asymptomatic re-infection lacked treponemicidal antibody. Sera from challenged rabbits with a relatively low degree of immunity to symptomatic disease showed endpoints of < or = 4. Rabbits with a relatively high degree of immunity to symptomatic reinfection and resistant to disseminated disease had endpoints that ranged from 6 to 96. Rabbits completely resistant to challenge exhibited endpoints ranging from 96 to 128.


CONCLUSIONS
Treponemicidal antibody measured by the "washed-killing" assay correlated closely with the status of immunity in experimental rabbit syphilis. Thus, antibody measured by this assay may be directed against key protective Treponema pallidum surface immunogens.
Lewinski
M A
MA
Department of Microbiology and Immunology, University of California School of Medicine, Los Angeles 90024.
Miller
J N
JN
Champion
C I
CI
Walker
E M
EM
Borenstein
L A
LA
Gayek
R J
RJ
Lovett
M A
MA
Blanco
D R
DR
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D003168:Complement Fixation Tests / Q000379:methods; D004195:Disease Models, Animal; D008297:Male; D010406:Penicillins / Q000627:therapeutic use; D011817:Rabbits; D012008:Recurrence; D013587:Syphilis / Q000097:blood / Q000188:drug therapy / Q000276:immunology*; D014209:Treponema Immobilization Test; D014210:Treponema pallidum / Q000276:immunology*
D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D010406:Penicillins