Detecting Green Fluorescent Protein-tagged Cryptococcus neoformans by Immunofluorescence on Paraffin-embedded Brain Sections

Cryptococcus neoformans is an important pathogen causing opportunistic fungal meningitis. The pathogenic mechanism of cryptococcal meningitis remains unclear. We aimed to describe a practical approach for studying the pathologic features of cryptococcal central nervous system infection by immunofluorescence on paraffin-embedded brain of mice using different antigen retrieval methods. After 14 days of intratracheal inoculation of green fluorescent protein-tagged C. neoformans (H99-GFP), C57BL/6J mice brains were fixed in 4% paraformaldehyde and embedded in paraffin. Antigen retrieval methods such as microwaves, 1% sodium lauryl sulfate, 1 N HCl, pepsase, and tryptase were used on 5-μm paraffin sections and the effects were compared. The green fluorescence of H99-GFP persisted with antigen retrieval using 1% sodium lauryl sulfate. After immunofluorescent staining, H99-GFP, glial fibrillary acidic protein-tagged astrocytes, and ionized calcium-binding adapter molecule 1-tagged microglia could be observed clearly. Based on our results, we provide a practical approach for the further study of the interaction between C. neoformans and brain cells.