An intravaginal live Candida challenge in humans leads to new hypotheses for the immunopathogenesis of vulvovaginal candidiasis

Abstract

Acute and recurrent vulvovaginal candidiasis (VVC) remains a significant problem in women of childbearing age. While clinical studies of women with recurrent VVC (RVVC) and animal models have provided important data about a limited protective role of adaptive immunity, there remains a paucity of information on the protective mechanisms or factors associated with susceptibility to infection. In the present study, an intravaginal live Candida challenge in healthy adult women showed a differential susceptibility to symptomatic VVC, where 3 (15%) of 19 women with no history of VVC acquired a symptomatic infection compared to 6 (55%) of 11 women with an infrequent history of VVC. Furthermore, these studies revealed that protection against infection is noninflammatory while symptomatic infection correlates with a vaginal infiltration of polymorphonuclear neutrophils (PMNs) and a high vaginal fungal burden. Thus, the presence of symptomatic infection appears more dependent on host factors than on properties of the organism. Finally, vaginal lavage fluid from women with a symptomatic infection, but not those asymptomatically colonized, promoted the chemotaxis of PMNs. These results suggest that rather than RVVC/VVC being caused by an aberrant adaptive immune response, symptoms that define infection appear to be due to an aggressive innate response by PMNs.

FIG. 1.

Presence of neutrophils in vaginal lavage fluid of women who acquired a symptomatic infection. Vaginal smears collected from women on different days postinoculation were fixed and stained using the Papanicolaou technique. (A) Smears from a woman who acquired a symptomatic infection. Times are days postinoculation. (B) Smears from a woman who became asymptomatically colonized. The results are representative of the general pattern seen in all women tested (n = 29). Magnifications are ×400 for each frame and ×1,000 (inset, day 7) and 120% of ×1,000 (inset, day 2/3).

FIG. 2.

Comparison of the outcomes of intravaginal inoculation with C. albicans in women without a history of VVC (level 1) and those with an infrequent history of VVC (level 2). A total of 19 level 1 and 11 level 2 women were evaluated. An infrequent history of VVC was defined as no more than two acute VVC episodes in a year that were explained based on the usual predisposing factors (antibiotic usage, high-estrogen oral contraceptives, hormone replacement therapy, pregnancy). Results were based on the criteria of symptomatic infection over the entire observation period (up to 14 days). Women with symptomatic infection were defined as having symptoms consistent with vaginitis, vaginal swabs positive for C. albicans, and hyphae or yeasts visible in KOH preparations of vaginal smears. Women with asymptomatic colonization had vaginal swabs positive for C. albicans. Women not colonized had no detectable CFU on vaginal swabs.

FIG. 3.

Vaginal fungal burden (A) and qualitative PMN score (B) before and after intravaginal inoculation. Results are from women who acquired a symptomatic infection (n = 9) compared to those who became asymptomatically colonized (n = 12). All women in the study irrespective of their history of VVC are represented. The PMN score listed for each woman was the mean for all visits. The mean PMN score for all women in a group was used to generate the graph. The criterion for PMN scoring is described in Materials and Methods. Pre and Post refer to pre- and postinoculation. SEM, standard error of the mean.

FIG. 4.

Ability of vaginal lavage fluid from women with symptomatic infection to induce PMN chemotaxis. Vaginal lavage fluid collected from women preinoculation (n = 4) or who acquired a symptomatic infection (n = 4) (infected), became asymptomatically colonized (n = 3) (colonized), or did not become colonized (n = 2) (not colonized) following inoculation with C. albicans was processed, sterile filtered, and tested in a PMN chemotaxis assay using a transwell chamber system. PMNs were acquired from normal volunteers. Lavage fluids were tested at 1:5 and 1:50 dilutions. The positive control was interleukin-8 (PMN chemokine), and the negative control was RANTES (T-cell chemokine). Other controls included CaCF, a 24-h supernatant of C. albicans blastoconidia cultured at 25°C (Candida sup), and PBS (vehicle for the lavage fluid). The chemotaxis index represents the ratio of cells in the experimental wells to those in the control well (chemotactic buffer). The horizontal line represents the line of positivity, above which active chemotaxis is considered positive. SEM, standard error of the mean.