Expression of the highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) in various types of cells in thymic tissues

Thymus, an important central immune organ in pigs, is the site of T lymphocyte development and maturation and an important target organ for infection and replication of various pathogens. Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) infection results in severe thymic atrophy in piglets. This study aimed to explore the effects of HP-PRRSV on the thymic structure of piglets to elucidate the pathogenesis of thymic atrophy induced by HP-PRRSV. In this study, histopathological techniques and immunofluorescence double staining techniques were used to analyze thymic tissues infected by HP-PRRSV to explore the structural changes of thymus caused by the viral infection and its target cell types. An antibody of cluster of differentiation (CD) 3 (CD3), CD20, CD80, or calgranulin + calprotectin was applied to identify T cells, B cells, dendritic cells (DCs), and macrophages, respectively. The results indicated that a variety of cell components in the thymic tissue were diffusely damaged after viral infection. In the infected thymic tissue, CD80- or calgranulin + calprotectin- -labeled cells supported the HP-PRRSV infection, whereas CD3-labeled T cells and CD20- -labeled B cells did not support the viral infection. The results showed that HP-PRRSV caused the reduction of visible cell components in the thymic tissue, and the virus attacked CD80- and calgranulin + calprotectin-positive cells (such as DCs and macrophages) in the thymic tissue, which played an important role in the pathogenesis of thymus atrophy. These results lay the foundation for elucidating the immunosuppression of piglets after infection with HP-PRRSV.