Time-Dependent Morphological Transformation of Penicillium marneffei by the Expression of YeastPhase Antigen in Liquid Culture and in THP-1 Cell Line

Abstract

Penicillium marneffei is a thermally dimorphic fungal pathogen associated with HIV infection. It causes penicilliosis, the third most common AIDS-defining illness in northern Thailand. Due to the considerable interest on the dimorphism of P. marneffei, it is hypothesized that the time required for P. marneffei to transition from its mold form to its yeast-like form affects the virulence of the organism inside the mammalian host. This study investigated the expression of a yeast-specific antigen in phase transition of P. marneffei by using the yeast-specific monoclonal antibody(MAb) 4D1. The conidia of P. marneffei were inoculated in 1% Proteose followed by harvest at 12-hour time intervals from 24 to 144 hours. Cells were then incubated with MAb 4D1 followed by fluorescently labeled secondary antibody. The percentage of P. marneffei positive yeast cells, detected by flow cytometry, increased gradually after longer incubation, in the range of 2.5-51.8 % of cells. In addition, THP-1 cells, were infected with P. marneffei at MOI=2 from 12 to 60 hours. Cells were harvested at 12-hour time intervals followed by staining using Mab 4D1 as described above. It was observed that 23.8% of the infected cells were positive at 24 hours of incubation, increasing to 61.85% after 36 hours. The dimorphism of P. marneffei in THP-1 was more rapid than found in liquid culture of 1% Proteose. The faster transformation of yeast cells in mammalian host cells than in liquid cell culture may suggest it being linked to better survival and increased virulence inside human and other mammalian hosts.