Evidence of apoptosis was detected for the UnitedStates porcine reproductive and respiratory syndrome virus (PRRSV) in ATCC CRL11171 cells inoculated with strain ATCC VR2385 and in the tissues of pigs infected with the same strain. Apoptosis was detected by agarose gel electrophoresis, transmission electron microscopy and terminal deoxytransferase dUTP nick end labelling (TUNEL) techniques. By electron microscopy and double-labelling techniques, apoptosis was detected primarily in uninfected bystander cells in the continuous cell line rather than the PRRSV-infected cells. In the lungs, the apoptotic cells were predominantly alveolar and pulmonary intravascular macrophages, and mononuclear cells in the alveolar septa. In the lymph nodes, the apoptotic cells were predominantly tingible body macrophages and mononuclear cells. The induction of apoptosis in a large number of mononuclear cells in the lungs and lymph nodes appears to be a mechanism of PRRSV pathogenesis and might be an explanation for a dramatic reduction in the number of alveolar macrophages and circulating lymphocytes and monocytes in PRRSV-infected pigs.Porcine reproductive and respiratory syndrome (PRRS), which has been recognized in the United States (US) since 1987 (Hill, 1990), is characterized by reproductive failure (stillborn, mummified and weak-born piglets) and respiratory disease in
The in situ hybridization (ISH) technique was developed to detect the swine coronaviruses, transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV), in cell culture and tissue sections from TGEV-or PRCV-infected pigs. The 35S-labeled RNA probes were generated from two plasmids pPSP.FP1 and pPSP.FP2 containing part of the S gene of TGEV. The procedure was first standardized in cell cultures. The radiolabeled pPSP.FP2 probe detected both TGEV and PRCV in virus-inoculated cell cultures, whereas pPSP.FP1 probe detected TGEV but not PRCV. The probe was then used to detect TGEV or PRCV in tissues of pigs experimentally infected with TGEV or PRCV or naturally infected with TGEV. Again, the probes detected TGEV in intestines of experimentally and naturally infected pigs and PRCV in the lungs of experimentally infected pigs. TGEV RNA was detected mainly within the enterocytes at the tips of villi and, less often, within some crypt epithelial cells. PRCV was shown to replicate mainly in the bronchiolar epithelial cells and in lesser amount in type II pneumocytes, type I pneumocytes, alveolar macrophages and bronchial epithelial cells, respectively. ISH has potential applications as a diagnostic test for the detection and differentiation of TGEV and PRCV in tissues and in studies to gain a better understanding of the mechanism of pathogenesis of enteric and respiratory coronavirus infections.
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