Establishment of an athymic BALB/c mouse model with chronic infection due to Phialophora verrucosa

Objective To establish an athymic (nu/nu) BALB/c mouse model with chronic subcutaneous infection due to Phialophora verrucosa (P. verrucosa) , and to explore the role of T lymphocytes in defensing against invasive infection due to P. verrucosa. Methods Six immunocompetent BALB/c mice and 6 nu/nu BALB/c mice were subcutaneously inoculated with 100 μl of P. verrucosa hyphae suspensions at a concentration of 5.0 × 108 colony-forming unit (CFU) /ml into one footpad, while another 6 immunocompetent BALB/c mice and 6 nu/nu BALB/c mice were subcutaneously inoculated with 100 μl of 5.0 × 108 CFU/ml P. verrucosa conidium suspensions into one footpad. The degree of footpad swelling was measured with a vernier caliper every 3 days. Histopathological characteristics of infected footpads were further analyzed. Biopsy tissues were also subjected to fungal culture to analyze the growth of P. verrucosa in infection foci in mice. Results After the treatment with hyphae or conidium suspensions, the BALB/c mice experienced transient footpad swelling within 12 days, and basically recovered after 50 days. However, the nu/nu BALB/c mice experienced persistent footpad swelling with recurrent ulceration and crusting. As pathological examination revealed, all the inoculation loci in BALB/c mice experienced local infection, and the morphology of P. verrucosa in the infected foci was not changed over time. However, invasive infections due to P. verrucosa hyphae alone or a mixture of P. verrucosa hyphae and sclerotic cells were observed in all the inoculation loci in nu/nu BALB/c mice. The fungal culture showed that P. verrucosa could not grow in the footpads of BALB/c mice after 21 days, while P. verrucosa could persistently grow in the footpads of nu/nu BALB/c mice. Conclusion An experimental model with subcutaneous phaeohyphomycosis due to P. verrucosa has been successfully established by using nu/nu BALB/c mice, and the nu/nu BALB/c mice are more susceptible to P. verrucosa infection compared with the immunocompetent BALB/c mice. Key words: Phialophora; Models, animal; Phaeohyphomycosis; Mice, nude; Philophora verrucosa; nu/nu BALB/c