Phagocytic uptake of Encephalitozoon cuniculi by nonprofessional phagocytes

Molecular characterization of Encephalitozoon intestinalis (Microspora) replication kinetics in a murine intestinal cell line

Microsporidia are obligate intracellular pathogens of invertebrate and vertebrate animals. Most human infections are caused by Enterocytozoon bieneusi or Encephalitozoon intestinalis, and result in chronic diarrhea. In order to determine the signals involved in microsporidial spore activation and invasion, kinetics of in vitro E. intestinalis replication were defined using real-time quantitative PCR. Segments of small subunit ribosomal RNA and polar tube protein 2 genes of E. intestinalis were used to quantify parasite gene copy number following infection in murine colon carcinoma cells. Parasite DNA was detectable in small but significant amounts within host cells as early as 4 h postinoculation, genome replication was completed by 36 h, and parasite progeny were released into the supernatant beginning 72 h postinoculation. Heat-treating spores did not prevent transfer of parasite DNA into cells, but did inhibit parasite replication. Treating cell cultures with albendazole suppressed but did not completely inhibit parasite replication. These results confirm observations that E. intestinalis completes its life cycle within the turnover time of its target host cells; invasion into susceptible host cells occurs independently of spore viability; and real-time quantitative PCR is a sensitive and reproducible method with which to monitor microsporidial infection under varying treatments or conditions.

Uptake of Aspergillus fumigatus Conidia by phagocytic and nonphagocytic cells in vitro: quantitation using strains expressing green fluorescent protein

Several pathogenic fungal organisms enter eukaryotic cells and manipulate the host cell environment to favor their own growth and survival. Aspergillus fumigatus is a saprophytic fungus that causes invasive lung disease in the immunocompromised host. To determine whether A. fumigatus could enter eukaryotic cells, we studied the uptake of two different GFP-expressing A. fumigatus strains into A549 lung epithelial cells, human umbilical vein endothelial (HUVE) cells, and J774 murine macrophages in vitro. A549 cells internalized 30% of the bound conidia whereas HUVE and J774 cells internalized 50 and 90%, respectively. Conidia within A549 cells remained viable for 6 h; however, 60 to 80% of conidia within J774 cells were killed after only 4 h. Live and heat-killed conidia were internalized to the same extent by A549 cells. After 6 h, almost none of the conidia inside A549 cells had germinated, whereas extracellular conidia had developed germ tubes. Internalization of conidia by A549 cells was a temperature-dependent process and required rearrangement of the underlying host cell cytoskeleton; uptake was inhibited by 75% with 0.5 microM cytochalasin D and by 65% with 5 microM colchicine. Fluorescent labeling of infected A549 cells with rhodamine phalloidin provided visible evidence of cytoskeletal alteration as many of the intracellular conidia were contained in actin-coated phagosomes. These data provide evidence that significant numbers of A. fumigatus conidia can be internalized by nonprofessional phagocytes in vitro and these cells may serve as reservoirs for immune cell evasion and dissemination throughout the host.