Dectin-1 stimulating β-glucans inhibit Chlamydia infections both in vitro and in vivo

Chlamydia trachomatis and Candida albicans are common inhabitants of the female genital tract. Candida albicans can impact the viability and pathogenesis of some bacteria. Previously, we investigated physical interactions between Ch. trachomatis elementary bodies (EBs) and Ca. albicans. This work indicated that EBs bind to Ca. albicans and become noninfectious by 24 h post-binding. Here, we continue our investigation of these interkingdom, polymicrobial interactions. Candida albicans adheres to bacteria or host surfaces via agglutinin-like sequence or heat shock 70 (Ssa) proteins. Chlamydia trachomatis EBs did not bind Ca. albicans Ssa2 deficient strains as efficiently as wild-type or complemented strains, indicating a role for this protein in chlamydial adherence to Candida. Additionally, Ca. albicans β-glucans inhibit chlamydial infection when exposure occurs during EB adsorption onto cervical cells. Laminarin, a β-glucan agonist of the C-type lectin receptor Dectin-1, inhibited chlamydial infection in both cervical epithelial cells and mice when exposure occurred prior to, during, or immediately following EB inoculation. Conversely, a Dectin-1 antagonist laminarin did not inhibit infection in vitro, suggesting that β-glucan inhibition of Ch. trachomatis requires C-type lectin receptor signaling. Overall, our data demonstrate that β-glucans from multiple species, including Ca. albicans, inhibit Chlamydia via stimulation of host-signaling pathways.