Novel insight into neutrophil immune responses by dry mass determination of Candida albicans morphotypes

PLoS One. 2013 Oct 30;8(10):e77993. doi: 10.1371/journal.pone.0077993. eCollection 2013.

Abstract

The common fungal pathogen Candida albicans has the ability to grow as a yeast or as a hypha and can alternate between these morphotypes. The overall biomass of both morphotypes increases with growth. However, only yeasts, but not hyphae, exist as discrete cellular entities. Multiplicity of infection (MOI) is a useful parameter to determine the initial inoculum of yeasts for in vitro infection assays. Since the amount of hyphae is difficult to quantify, comparable starting conditions in such assays cannot be determined accurately for yeasts and hyphae using MOI. To circumvent this problem, we have established a set of correlation coefficients to convert fungal metabolic activity and optical density to dry mass. Using these correlations, we were able to accurately compare ROS production and IL-8 release by polymorphonuclear neutrophils upon infection with equal dry mass amounts of yeast and hyphal morphotypes. Neutrophil responses depended on the initial form of infection, irrespective of C. albicans wild-type yeasts transforming to hyphal growth during the assay. Infection with a high mass of live C. albicans yeasts resulted in lower neutrophil ROS and this decrease stems from efficient ROS detoxification by C. albicans without directly affecting the phagocyte ROS machinery. Moreover, we show that dead C. albicans induces significantly less ROS and IL-8 release than live fungi, but thimerosal-killed C. albicans were still able to detoxify neutrophil ROS. Thus, the dry mass approach presented in this study reveals neutrophil responses to different amounts and morphotypes of C. albicans and serves as a template for studies that aim to identify morphotype-specific responses in a variety of immune cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Candida albicans / immunology*
  • Candida albicans / pathogenicity*
  • Cell Survival
  • Cells, Cultured
  • Humans
  • Interleukin-8 / metabolism
  • Neutrophils / immunology*
  • Neutrophils / metabolism
  • Reactive Oxygen Species / metabolism

Substances

  • Interleukin-8
  • Reactive Oxygen Species

Grants and funding

This work was supported by grants from the Swedish Research Council VR-M (K2012-99X-21961-01-3), the Laboratory for Molecular Medicine Sweden (MIMS)and the Medial Faculty Umeå (316-886-10). AH acknowledges financial support from the J.C. Kempes Memorial Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.