Inhibition of Monocytic Interleukin-12 Production byCandida albicansvia Selective Activation of ERK Mitogen-Activated Protein Kinase

Abstract

Our previous data demonstrated that live Candida albicans inhibits interleukin-12 (IL-12) production by human monocytes. Here we explored whether C. albicans inhibits IL-12 via a released factor and whether the inhibition is mediated via mitogen-activated protein kinase (MAPK) regulation. Supernatant fluids were obtained from cultured C. albicans (SC5314) as well as cultured Saccharomyces cerevisiae after 20 h of incubation. At 2 h postincubation of monocytes with heat-killed C. albicans (HKCA) (2:1) to stimulate IL-12, concentrated fungal supernatant fluids were added and incubated for an additional 20 h. The present data show that, unlike supernatant fluids obtained from S. cerevisiae, the C. albicans supernatant fluids significantly suppressed IL-12 production induced by HKCA. This suggested that the inhibition is Candida specific. A preliminary biochemical analysis revealed that this secretory IL-12 inhibitory factor is glycoprotein in nature. The inhibitory activity had no effect on the phagocytosis of yeasts. Supernatant fluids from C. albicans markedly induced the phosphorylation of ERK44/42 MAPK, but not p38 and SAPK, 1 min after they were added to monocytes. To test if the induction of ERK44/42 MAPK was central to the IL-12 inhibition, we used gamma interferon (IFN-␥) (1 ng/ml) plus lipopolysaccharide (LPS) (100 ng/ml) to stimulate IL-12 production by monocytes. The inhibition of ERK MAPK by the specific inhibitor PD 98059 significantly reduced phospho-ERK44/42 MAPK levels induced by C. albicans supernatant fluids in the IFN-␥-plus-LPS-driven monocytes. Concomitantly, PD 98059 reversed the IL-12 inhibitory activity of the C. albicans supernatant (P < 0.01). These data indicate that C. albicans can inhibit IL-12 production by secreting an ERK44/42 MAPK-stimulating factor and thus can attenuate effective immune responses.

Interplay between Candida albicans and the Mammalian Innate Host Defense

“…This IL-12 inhibitory effect was dependent on the viability of C. albicans, because both heat-killed C. albicans and C. krusei induced similar amounts of IL-12. Further studies showed that IL-12 inhibitory activity is due to the secretion of a glycoprotein (112) and signaling through the selective activation of extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) (102). However, the identities of this soluble glycoprotein and the receptor responsible for the IL-12 inhibition signaling are unknown.…”

Interaction ofCandida albicanswith Adherent Human Peripheral Blood Mononuclear Cells IncreasesC. albicansBiofilm Formation and Results in Differential Expression of Pro- and Anti-Inflammatory Cytokines

“…To determine whether the biofilmenhancing effect of PBMCs is specifically associated with the activation of these immune cells by C. albicans biofilms, we tested whether PBMCs activated by a nonbiofilm source can also enhance biofilm formation. The activation method selected was exposure to LPS, a method which has previously been used to activate PBMCs (4,40). Adherent PBMCs were activated with LPS, and the ability of this LPS-induced PBMC supernatant to influence the ability of C. albicans to form biofilm was then determined.…”

“…To examine the interactions between host immune cells and Candida biofilms, PBMCs were extracted from peripheral blood as described previously (39,40). Briefly, the collected blood was diluted (1:1) with Hanks' balanced salt solution (HBSS; Mediatech Inc., Herndon, VA), and 30 ml of this diluted blood was layered on a Histopaque density gradient (Sigma-Aldrich, St. Louis, MO) and centrifuged at 1,500 rpm for 40 min at 24°C.…”

“…Candida spp. have been shown to have immunomodulatory activity mediated by fungal factors, including mannan and glycoproteins, mannoprotein constituents of the cell wall, and surface antigens (5,9,40,47). Although interactions occurring between the host immune system and Candida have been investigated in some detail for planktonically grown Candida cultures (reviewed in references 31, 33, 34, 35, and 38), no information is currently available for such interactions in a biofilm environment.…”

Gene expression profile of THP-1 cells treated with heat-killed Candida albicans

“…For example, we found that the downregulated genes were involved in mitogen-activated protein kinases (MAPKs) signaling pathway. MAPK is a family of serine/threonine kinases that participates in pathogen- (7) and human monocytes (8), which could promote the phagocytosis of C. albicans and inhibit IL-12 production. In addition, Dectin-1 has been reported to be one of the pattern recognition receptor in innate immune sensing of C. albicans (9).…”