The complement (C) system plays an important role in host defence against microbial agents both in the circulation and at tissue level. The protective function of C may be critical at sites, such as the cervico-vaginal cavity and mucosa that are continuously exposed to several of these agents. We have found that the three recognition molecules of the C system, C1q, MBL and C3b, are present in the cervico-vaginal lavage (CVL) and exhibits selective reactivity for different targets. Thus, MBL and C3b bind to Gardnerella vaginalis and Candida albicans, although the binding of MBL to Candida is pH dependent, while C1q fail to recognize these agents. This suggests that the lectin and classical pathways of C activation may play a different role in immune defence in the female genital tract. We have also evaluated whether the level of MBL in the CVL is under hormonal influence and if this C component derives from the circulation or is locally produced. To this end, the level of MBL was measured in the CVL and found to increase during the luteal phase of the menstrual cycle, while the level of transferrin, a liver-derived plasma protein, remained constant in the proliferative and the luteal phases. These findings suggest that MBL is, at least in part, locally produced. Immunohistochemical analysis of the cervico-vaginal mucosa for the distribution of MBL showed that this protein was deposited on the basal membrane. In situ hybridization revealed that epithelial cells of the basal layer are the main site of synthesis. Vaginal mucosa seems to be the local source of MBL because the concentration of MBL in the CVL of women undergoing hysterectomy does not change after hysterectomy.
