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Porcine circovirus type 2 (PCV2) and swine influenza virus (SIV) are important pathogens for porcine respiratory disease complex, which is economically significant worldwide. The pathogenesis of PCV2-SIV coinfection is unknown. In this study, we focused on establishing a challenge model for PCV2 to determine whether SIV influences PCV2 replication and increases the severity of PCV2-associated disease. Cesarean-derived colostrum-deprived pigs were inoculated intratracheally with cell culture medium only (negative control group), PCV2 only, or PCV2 followed 1 wk later with SIV H1N1. Two pigs from each group were necropsied at 12, 21, 28, and 35 d after inoculation. Coinfection with SIV did not increase the number of PCV2 genomic copies in serum or target tissues or the severity of microscopic lesions associated with PCV2 in lung or lymph node. The antibody titer to PCV2 did not differ significantly between PCV2-SIV- and PCV2-infected groups. In conclusion, SIV H1N1 did not influence PCV2 replication in dually infected pigs in this study.

Focal accumulations of mononuclear cells in the arterial wall of healthy humans at predilection sites for atherosclerotic lesions have been described as 'vascular-associated lymphoid tissue' (VALT). Here we investigated whether pigs (Sus scrofa), a commonly used animal model for studying cardiovascular disease, have VALT. Samples of major arteries were collected from 10 conventional crossbred pigs (age, 2 to 24 mo) and processed for routine light microscopy, immunohistochemistry, and immunofluorescence. Single or small aggregates of mononuclear cells were noted in the intima and occasionally the inner portion of the tunica media and adventitia at branching sites. The infiltrating cells were primarily CD3+CD4+ T cells, with some macrophages. No CD8+ T cells were present. Infiltrating leukocytes and overlying endothelial cells frequently expressed major histocompatibility class II molecules. Two Ossabaw pigs on low-fat diet had similar leukocytic aggregates at locations where animals of the same breed but fed a high-fat and high-cholesterol diet developed atherosclerotic lesions. Further, the densities of CD3+ T lymphocytes and in these areas were decreased in 2 sedentary and 2 exercised Ossabaw pigs on an atherogenic diet compared with conventional crossbred and Ossabaw pigs on a normal diet. This study shows that focal aggregates of lymphocytes occur in the vasculature of pigs at locations predisposed to development of atherosclerotic lesions. These cellular aggregates are similar to the structures described as VALT in human arteries and reinforce the value of the pig as a model for the study of human cardiovascular disease.