OBJECTIVE: The purpose of this study was to investigate the possible a
ntichlamydial activity of vaginal secretion and to partially character
ize the inhibitory principle. STUDY DESIGN: Vaginal secretions obtaine
d from 156 women attending a family planning or gynecologic outpatient
clinic for contraceptive advice were studied for the influence on the
inclusion formation of Chlamydia trachomatis in cycloheximide-treated
McCoy cell cultures. RESULTS: Vaginal secretions from 156 women inhib
ited the inclusion formation of Chlamydia trachomatis. The inhibition
was concentration dependent and the inhibitory principle had a molecul
ar weight of <10,000 d. It was heat labile. It was not related to anti
chlamydial antibodies in vaginal secretions. Only three (2%) of the wo
men had a positive culture for Chlamydia trachomatis. Three had immuno
globulin A and three had immunoglobulin G antichlamydial antibodies in
vaginal secretions. Secretions or those with a vaginal pH of 3.5 to 4
.5 decreased the chlamydial inclusion count by 75% compared with contr
ols. The corresponding percentage for those with a pH of 5.0 to 6.0 wa
s 48% and for those with pH > 6 was 33%. Vaginal secretions of oral co
ntraceptive users and nonusers did not differ in the capacity to decre
ase the chlamydial inclusion count, p > 0.01. CONCLUSIONS: When vagina
l secretions were added to McCoy cell cultures infected by Chlamydia t
rachomatis, the chlamydia inclusion number decreased. There was a corr
elation between pH of the vaginal secretion and the inhibitory princip
le. Oral contraceptive use had no influence on the inhibition.