In vivo imaging and analysis of host-pathogen interactions of intracellular pathogens

Cellular and extracellular host-pathogen interactions are important in the progression of infection. Extracellular survival and growth can be significant for pathogen dissemination. Equally, intracellular pathways, such as autophagy, can be employed in host cell defence. Autophagy is a cellular self-degradation process that recycles cellular components through lysosomal degradation. Primarily for regulating starvation and housekeeping pathways, autophagy is also important for degradation of invading intracellular pathogens. Selective autophagy receptors can also target pathogens for autophagic degradation. However, some intracellular pathogens are able to subvert or block host cell autophagy. Cryptococcus neoformans and Staphylococcus aureus represent fungal and bacterial pathogens which can reside either intracellularly or extracellularly. The role of host cell autophagy in C. neoformans and S. aureus infection is unclear. Infection of zebrafish with C. neoformans or S. aureus enabled in vivo imaging of host-pathogen interactions, to examine infection growth dynamics and dissemination, in addition to cellular level imaging of pathogen interactions with host cell autophagy components.

Cryptococcal infection can cause cryptococcal meningitis, frequently associated with cerebral infarcts. Analysis of cryptococcal proliferation during infection suggested that formation of intravascular cryptococcal masses precedes invasion of surrounding tissue. Vessel integrity analysis highlighted cryptococcal-mediated vascular damage, potentially providing a route for tissue dissemination. Vasculature damage may explain the origin of cortical infarcts in disease.

Autophagy mutant zebrafish were generated to analyse host autophagy in pathogen infection. Characterisation of mutant larvae revealed a clear survival and growth defect, indicating autophagy is required for larval development. Autophagy mutants were subsequently used to analyse the role of autophagy during infection through analysis of pathogenic burden and pathogen association with autophagosome marker LC3-II. LC3II recruitment to pathogens was reduced in autophagy mutant neutrophils. Additionally, selective autophagy receptor p62 was recruited to S. aureus and C. neoformans within neutrophils, highlighting the involvement of host cell autophagy during infection.