Apoptosis in feline panleukopenia virus-infected lymphocytes

Abstract

Feline panleukopenia virus (FPLV) was shown to induce apoptosis to feline lymphoid cells and to reduce the expression of interleukin-2 receptor alpha on the cells. FPLV-induced apoptosis might be a key element in the pathophysiology of atrophy of lymphoid tissues associated with feline panleukopenia caused by FPLV.

FIG. 1

Susceptibilities of feline cells to FPLV. (A) Growth curves of strain TU1 in feline lymphoid cells. Feline cells were inoculated with TU1 and collected at the indicated times. FPLV antigen-positive rates in the cells were measured with an anti-FPLV VP2 MAb. Symbols: ○, mock-inoculated cells; •, TU1-infected cells. (B) CPEs observed in FPLV-inoculated feline PBMCs and FL74 cells. FPLV-inoculated or mock-inoculated feline PBMCs and FL74 cells were harvested at 2 days and 1 day p.i., respectively. (C) Electrophoresis of total cellular DNA. Cellular DNA was extracted from cultures of inoculated or mock-inoculated PBMCs and MYA-1 and FL74 cells. Lanes 1, FPLV-inoculated cells at 1 day p.i.; lanes 2, 2 days p.i.; lanes 3, 3 days p.i.; lanes 4, 4 days p.i.; Mock, mock-inoculated cells at 4 days p.i. The extracted DNAs were analyzed by 1.7% agarose gel electrophoresis.

FIG. 2

Morphologies of FPLV-infected lymphocytes. (A) Detection of DNA strand breaks in FPLV-inoculated cells by the TUNEL assay. FPLV-inoculated or mock-inoculated PBMCs and MYA-1, FL74, and CRFK cells were harvested at 2, 2, 1, and 8 days p.i., respectively (B) Flow cytometric analysis of TUNEL-positive rates in the inoculated cells. The inoculated cells were collected at the indicated times and analyzed by FACScan. Symbols: ○, mock-inoculated cells; •, TU1-inoculated cells. (C) Electron microscopic analysis of infected PBMCs. FPLV-inoculated or mock-inoculated PBMCs were harvested at 2 days p.i. Arrowheads indicate cells showing chromatin condensation along the inner aspect of the nuclear membrane. Bars, 1 μm.

FIG. 3

Effects of FPLV infection on feline IL-2Rα of inoculated feline lymphoid cells. Flow cytometric analysis was performed with FPLV-inoculated feline PBMCs and MYA-1 cells at 2 or 3 days p.i. Three independent experiments were performed, and the averages and standard deviations of mean fluorescence intensities (MFI) are presented. The results of flow cytometric analyses are representative of one of the three independent experiments.

FIG. 4

Susceptibilities of feline and canine cells to CPV. (A) Cell viabilities of FPLV- or CPV-inoculated feline and canine lymphoid cells. Feline and canine cells were inoculated with strain TU1 or strain Cp49 and collected at the indicated times. Symbols: ○, mock-inoculated cells; •, TU1-inoculated cells; □, Cp49-inoculated cells. (B) CPEs observed in CPV-inoculated CL-1 cells. CPV-inoculated or mock-inoculated CL-1 cells were harvested at 5 days p.i. (C) Electrophoresis of total cellular DNA. Cellular DNA was extracted from cultures of FPLV-inoculated (lanes 1), CPV-inoculated (lanes 2), or mock-inoculated (lanes 3) feline PBMCs (fPBMCs), FL74 cells, and canine PBMCs (cPBMCs). The inoculated fPBMCs, FL74 cells and cPBMCs were harvested at 4, 2, and 4 days p.i., respectively. The extracted DNAs were analyzed by 1.7% agarose gel electrophoresis. (D) Electrophoresis of total cellular DNA of the CPV-inoculated CL-1 cells. Cellular DNA was extracted from cultures of inoculated or mock-inoculated CL-1 cells. Lane 1, CPV-inoculated cells at 1 day p.i.; lane 2, 2 days p.i.; lane 3, 3 days p.i.; lane 4, 4 days p.i.; lane 5, 5 days p.i.; Mock, mock-inoculated cells at 4 days p.i. The extracted DNAs were analyzed by 1.7% agarose gel electrophoresis.