ABSTRACT
Candidemia is the most frequent invasive mycosis in hospitalized patients worldwide. Fungal infection in central nervous system is a life-threatening complication which aggravates patients' prognosis. This article summarizes relevant aspects on the clinical characteristics of this pathology, mechanisms of fungus invasion, local immune response to Candida albicans and the impact of genetic defects on innate immune receptors that increase susceptibility to the acquisition of this form of mycosis.
Subject(s)
Candidiasis, Invasive , Central Nervous System Infections , Candida albicans , Candidiasis, Invasive/diagnosis , HumansABSTRACT
After Candida albicans arrival to the liver, the local production of proinflammatory cytokines and the expanded intrahepatic lymphocytes (IHL) can be either beneficial or detrimental to the host. Herein we explored the balance between protective inflammatory reaction and liver damage, focusing our study on the contribution of TNF-α and Fas-Fas-L pathways in the hepatocellular apoptosis associated to C. albicans infection. A robust tissue reaction and a progressive increase of IL-1ß, IL-6 and TNF-α were observed in infected animals. Blocking the biological activity of TNF-α did not modify the number of apoptotic cells observed in C. albicans infected animals. Fas-L molecule was up regulated on purified hepatic mononuclear cells and its expression progressed with the infection. In the IHL compartment, the absolute number of Fas-L+ NK and NKT cells increased on days 1 and 3 of the infection. C. albicans was also able to up regulate Fas-L expression in normal liver NK and NKT cells after in vitro contact. The innate receptor TLR2 was involved in this phenomenon. In the interplay between host factors and evasion strategies exploited by pathogens, the mechanism supported here could represent an additional way that allows this fungus to circumvent protective immune responses in the liver.
Subject(s)
Candida albicans/immunology , Fas Ligand Protein/genetics , Gene Expression Regulation , Killer Cells, Natural/immunology , Killer Cells, Natural/metabolism , Natural Killer T-Cells/immunology , Natural Killer T-Cells/metabolism , Animals , Apoptosis , Chemokines/genetics , Chemokines/metabolism , Cytokines/genetics , Cytokines/metabolism , Female , Hepatocytes/immunology , Inflammation/immunology , Inflammation/metabolism , Inflammation/microbiology , Inflammation/pathology , Liver/immunology , Liver/metabolism , Liver/microbiology , Liver/pathology , Rats , Signal Transduction , Toll-Like Receptor 2/genetics , Toll-Like Receptor 2/metabolism , Tumor Necrosis Factor-alpha/metabolismABSTRACT
Hepatic mononuclear cells (HMC) are a heterogeneous population with innate immune properties involved in the response to several pathogens. Herein, during the primary infection with Candida albicans, we observed dynamic changes in CD3+, NK+ and NKT+ intrahepatic lymphoid subsets and a significant increase in the absolute number of antigen-presenting cells (APC). The liver tolerogenic microenvironment sustained by higher levels of IL-10, transforming growth factor-ß and IL-4 was severely modified upon the robust IFN-γ production after the fungal colonization. NKT cells purified from infected animals released significant amounts of IFN-γ and the production of this cytokine was exacerbated after a second contact with the fungus. Interestingly, C. albicans per se was unable to activate tolerogenic NKT cells from naive animals. In vitro experiments performed with HMC cells depleted of the CD11b/c+ population revealed that in the absence of APC, NKT cells are unable to produce IFN-γ in response to C. albicans. Our findings constitute the first evidence that this innate lymphocyte population is involved in the pathogenesis of C. albicans infection.
