Features of Cell Degeneration and Death in Hepatic Failure and Systemic Lymphoid Depletion Characteristic of Porcine Circovirus-2–associated Postweaning Multisystemic Wasting Disease

Abstract

Abstract. Tissue section replicates from lymphoid tissues and livers of gnotobiotic swine were examined by immunohistochemistry for the colocalization of porcine circovirus-2 (PCV-2) nucleocapsid and terminal deoxynucleotidyl transferase (TdT)-mediated incorporation of biotinylated nucleotides (UTP) onto the 3Ј-exposed hydroxyl groups (nick end labeling) nuclear deoxyribonucleic acid (TUNEL), a marker for apoptosis. Single-and dually stained replicates from uninfected controls, subclinically affected PCV-2-infected gnotobiotic pigs, PCV-2-infected piglets immunosuppressed with cyclosporine (Cys), and PCV-2-infected piglets with postweaning multisystemic wasting syndrome (PMWS) were evaluated. Thymuses were used as positive controls for apoptosis absent PCV-2, tissue sections from dogs given hyperthermic stress were examined as positive controls for induced TUNEL. Tissues from heat-stressed dogs contained TUNEL-positive cell nuclei in both lymphoid tissues and liver, TUNEL was greatest shortly after the delivery of the hyperthermic insult. In uninfected control and subclinically affected PCV-2-infected gnotobiotic pigs, rare hepatocytes and lymphoid cells were TUNEL positive, the frequency of these was similar to that seen in uninfected controls. In PMWS-affected and Cys-treated PCV-2 piglets, the only consistent strongly positive TUNEL signal was contained within the cytoplasm of virus-positive phagocytic mononuclear cells. In phagocytes, some PCV-2 inclusions were TUNEL positive. Collectively, these data indicate that apoptosis is not the primary mechanism of lymphoid depletion and hepatocyte loss in PMWS. Apoptosis associated with systemic viral diseases may be attributable to pyrexia rather than direct or indirect effects of viruses on target cells.

Singular PCV2a or PCV2b infection results in apoptosis of hepatocytes in clinically affected gnotobiotic pigs

“…Little to no apoptosis was found in archived paraffin-embedded blocks of formalin-fixed and cold ethanol-fixed liver, lymph nodes, spleen and thymus obtained from clinically-affected and unaffected gnotobiotic pigs (Krakowka et al, 2004). This is in contrast to the outcomes obtained in the current study and may be due to the fact that lower numbers of pigs were used in the previous study (Krakowka et al, 2004) as well as different challenge virus and different tissues were evaluated.…”

“…PCV2 infection in gnotobiotic pigs has been found to result in liver failure associated with icterus which becomes the imminent cause of death in pigs with this manifestation of PCVAD (Krakowka et al, 2004). The current study used experimentally PCV2-inoculated gnotobiotic pigs with and without signs of clinical disease and hepatic failure.…”

“…Therefore, results obtained on field cases need to be viewed with caution. Studies conducted by several research groups have identified apoptosis by TUNEL assay (Shibahara et al, 2000;Krakowka et al, 2004;Mandrioli et al, 2004;Resendes et al, 2004a;Seeliger et al, 2007) and CCasp3 IHC (Resendes et al, 2004a,b;Seeliger et al, 2007) in conventional, clinically-affected pigs (Rosell et al, 1999(Rosell et al, , 2000b. A recent investigation on conventional pigs using the TUNEL assay, CCasp3 IHC and PCV2 in situ hybridization (ISH) provided evidence of virus-induced apoptosis in endothelial cells in pigs diagnosed with PCV2-associated cerebellar vasculitis (Seeliger et al, 2007).…”

“…After the tissues were fixed for 24 h, the tissues were dehydrated, paraffin-embedded, sectioned at 4 lm and mounted on a glass slide followed by routine hematoxylin/eosin staining as described (Krakowka et al, 2004).…”

“…doi:10.1016/j.rvsc.2010.10.013 classical swine fever and many others (Roulston et al, 1999). Microscopically, apoptosis can be demonstrated by dUTP labeling of single strand DNA breaks in the nucleus (Krakowka et al, 2004) or by demonstrating the presence of cleaved caspase 3 (CCasp3) by immunohistochemistry (IHC) staining (Resendes et al, 2004a,b). A novel open reading frame (ORF3) was identified in PCV2 infected PK15 cells in 2005.…”