Principles of Fungi

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:

These are 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.

Fungi classically are grouped into 2 types of pathogens:

Systemic pathogens:

– High virulence organisms which affecting all people

– These enter through lungs but often asymptomatic

Systemic opportunists:

– These are low virulence organisms which usually affect only immunocompromised patients, but can cause severe disease

– They can enter the body from any site

Immunity 

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