Fungi are eukaryotes with a nucleus, cytoplasm and a cell membrane made of ergosterol.
– They also have a cell wall made of an outer matrix of B-1,3-linked glucans and inner layer of chitin, which is made up of chains of B-1,4-linked n-acetyl glucosamine.
Fungi can exist in many different forms:
– Yeasts –> round unicellular organisms which multiply asexually by a process called budding
– Filamentous moulds –> these form hyphae, which form an interwoven mass called a mycelium
– Dimorphic –> These change morphologies depending on the external environment.
They give 2 main types of systemic infections:
– Systemic pathogens –> High virulence affecting all people – enters through lungs but often asymptomatic
– Systemic opportunists –> Low virulence affecting only immunocompromised. Enters through anywhere
Immunity to fungi is generally mediated by pattern recognition receptors which recognise fungal PAMPs
– This leads to inflammation and release of inflammatory cytokines which upregulate cell immunity
– IL-6 and IL-23 up-regulate Th17 cells –> leads to recruitment of neutrophils
– IL-12 and TNFa up-regulate Th1 –> leads to recruitment of macrophages to phagocytose fungi