Poxvirus-induced immunostimulating effects on porcine leukocytes

The prophylactic application of inactivated parapox ovis viruses (Baypamun; Bayer AG, Leverkusen, Germany) has been shown. to reduce efficiently the o utbreak of stress-mediated diseases in different species. However, little i s known about the basic mechanism behind this observed stimulatory property . We therefore tested eight inactivated pox-virus strains belonging to thre e different genera (Orthopoxvirus, Avipoxvirus, and Parapoxvirus) for their capacity to activate cells of the porcine innate and specific immune syste ms in vitro. The results indicated that poxviruses failed to induce increas ed phagocytosis, oxidative burst, or natural killer cell activity in swine. In contrast, enhanced release of interleukin-2, alpha interferon, and gamm a interferon, as well as strong proliferation, could be measured. Flow cyto metric analyses and cell sorting experiments identified T-helper cells as t he main target responding to inactivated poxviruses: the activated cells ha d a CD4(high) CD25(+) major histocompatibility complex type II-positive phe notype and were the major source of secreted cytokines. Together, the resul ts demonstrated that all tested poxviruses possessed immunostimulating capa city.;These in vitro poxvirus-induced effects may be responsible at least i n part for the in vivo immunostimulating capacity of inactivated poxviruses .