Mannose binding lectin and C3 act as recognition molecules for infectious agents in the vagina

Abstract

In our study we examined the early complement components in patients with bacterial vaginosis (BV), vulvovaginal candidiasis (VVC) and in healthy controls. The levels of C1q, mannose-binding lectin (MBL) and C3 were measured by ELISA in the cervicovaginal lavage (CVL) from gynaecological patients and controls. No significant differences were observed in the levels of these proteins in the three study groups. Immunofluorescence analysis of the clue cells and Candida hyphae from BV and VVC patients for surface-bound complement components showed the presence of C3, while C1q was undetectable. MBL was revealed on clue cells but not on Candida. Binding of MBL to Candida, grown or cytocentrifuged from the CVL of VVC patients, was found to be pH dependent and occurred between pH 4.5 and pH 5.5. In conclusion, we demonstrated that MBL and C3 present in the vaginal cavity act as recognition molecules for infectious agents that colonize the cervicovaginal mucosa. Our finding that MBL, but not C1q, binds to bacteria and fungi in vagina suggests that the lectin and classical pathways of complement activation may play a different role in immune defence in the female genital tract.

Fig. 1

Levels of (a) MBL, (b) C1q and (c) C3 in the CVL obtained from control women and from patients with BV and VVC and measured by ELISA. The results are expressed as total amount of each components present in 10 ml of CVL. Comparison of the data obtained in the study groups did not reveal statistical difference (P > 0·01).

Fig. 2

Microscopic and immunofluorescence analysis of epithelial cells present in the CVL obtained from two patients (A and B) with BV. The two left panels show several epithelial cells detected in the cytocentrifugates of the cell suspension and among them clue cells indicated by arrows. The other panels show the results of the immunofluorescence analysis of the same cells for cell bound MBL, C1q and C3. Note that C1q is almost undetectable, while both MBL and C3 are present exclusively on the surface of clue cells.

Fig. 3

Analysis of G. vaginalis for the binding of (b) MBL, (c) C1q and (d) C3. The bacterial suspension was air dried on a glass slide, fixed with 1·5% paraformaldehyde and incubated either with serum diluted 1 : 2, to evaluate the binding of C3 and C1q, or with purified MBL (5 µg/ml). (a) G.vaginalis viewed under microscopy. Note that the bacteria stained for MBL and C3, but not for C1q. (Magnification × 1000)

Fig. 4

Microscopic and imunofluorescence analysis of Candida albicans isolated from the CVL of a VVC patient. Candida hyphae, indicated by arrows, are seen in the cytocentrifugates of the CVL (a) and stained for immunofluorescence analysis in the other panels. Note that Candida hyphae stain only for C3 (d), but not for MBL (b) and C1q (c). (Magnification × 250)

Fig. 5

Effect of pH on the binding of MBL to Candida. The analysis was performed on Candida obtained by cytocentrifugation of the CVL from a VVC patient (b) or grown in a selective medium (a). The fungi were incubated with MBL at three different pH and then exposed to specific antibody. Note the increase of MBL with the rise in pH. (Magnification × 250)