Porcine reproductive and respiratory syndrome virus (PRRSV) is frequently associated with various other pathogens, suggesting that the virus leads to secondary infections by disturbing host defense mechanisms. It is still unknown whether PRRSV could affect immune tissues. In this study we clarified immunohistochemically the target organs and cells of the virus and the early alterations of lymphocyte subpopulations of lymphoid tissues in pigs infected with the virus. PRRSV antigens were detected in all lymphoid tissues from the early stage of infection, indicating that the virus infects lymphoid tissues as target organs. Double immunohistochemical staining for PRRSV antigen and macrophage markers revealed that the cells presenting the virus antigen were almost macrophages, but not lymphocytes. However, early changes of lymphocyte subpopulations were observed in several lymphoid tissues; increase in the number of CD8+ cells in spleen and superficial inguinal lymph node, and also increase in number of B-cells in Peyer's patch. These results suggest that PRRSV dose not infect lymphocytes but affects lymphocyte subpopulations in immune tissues from the early stage of infection.
(Lab. of Environmental Hygiene, Shichinohe Research Unit)
