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Interactions between Candida species and platelets
M D Willcox1, B C Webb, A Thakur
1Cornea and Contact Lens Research Unit, School of Optometry and Cooperative Research Centre for Eye Research and Technology, University of New South Wales, Australia.
Abstract:
Candida spp. are able to cause disseminated disease in immunocompromised patients. This study examined the interactions of Candida spp. with platelets, complement and polymorphonuclear leucocytes (PMNLs). With the exception of C. albicans, all other Candida spp., including a C. albicans strain previously classified as C. stellatoidia, aggregated human platelets at a ratio of yeast cells: platelets of 1:80. Usually, those species and strains that aggregated platelets were either killed or prevented from growing in platelet-rich plasma indicating that the aggregation released microbicidal or microbistatic substances that were active against Candida spp. All Candida spp. were resistant to attack by complement in 50% serum. However, all species activated complement as determined by the presence of C3 fragments on their surface, in particular a 195-kDa fragment corresponding to C3c, two fragments at 67 and 40 kDa corresponding to iC3b, and a 33-kDa fragment corresponding to C3d. When strains were tested for their ability to stimulate the release of pro-inflammatory substances from platelets and PMNLs, it was found that most strains stimulated PMNLs to release interleukin(IL)-8 but not IL-1beta or leucotriene B4. The ability of C. albicans to evade complement-mediated killing and not to aggregate platelets may contribute to the survival of this species in the blood during vascular infections.
Insights
Candida species interact with immune cells, with most aggregating platelets and releasing antimicrobial substances. Candida albicans evades platelet aggregation and complement killing, potentially aiding its survival in disseminated infections.
Area of Science:
- Mycology
- Immunology
- Infectious Diseases
Background:
- Candida species are opportunistic fungal pathogens capable of causing severe disseminated infections, particularly in immunocompromised individuals.
- Understanding the interactions between Candida and host immune components is crucial for explaining pathogenesis and developing therapeutic strategies.
Purpose of the Study:
- To investigate the interactions of various Candida species with human platelets, complement system, and polymorphonuclear leukocytes (PMNLs).
- To elucidate the mechanisms by which Candida species may evade host immune responses during disseminated infections.
Main Methods:
- Yeast-human platelet aggregation assays were performed at a 1:80 ratio.
- Complement resistance and activation were assessed using 50% serum, with C3 fragment deposition analyzed.
- The release of pro-inflammatory cytokines (IL-8, IL-1beta) and leukotriene B4 from platelets and PMNLs upon Candida stimulation was measured.
Main Results:
- Most Candida species, excluding Candida albicans, aggregated human platelets, leading to yeast killing or growth inhibition.
- All tested Candida species were resistant to complement-mediated lysis but activated the complement system, evidenced by C3 fragment deposition (C3c, iC3b, C3d).
- Candida strains primarily stimulated PMNLs to release interleukin-8 (IL-8), but not IL-1beta or leukotriene B4.
Conclusions:
- Candida albicans's inability to aggregate platelets and its resistance to complement-mediated killing may contribute to its increased virulence and survival in the bloodstream during invasive infections.
- Platelet aggregation by other Candida species appears to be an important host defense mechanism, releasing antimicrobial factors.
- Differential interactions with immune cells highlight the complex host-pathogen dynamics in Candida infections.