Evidence for a parapox ovis virus-associated superantigen

As shown in a number of species, susceptibility to infectious diseases can be efficiently reduced following application of inactivated parapox ovis vi ruses (iPPOV). However. the basic mechanism for this stimulating capacity o f iPPOV remains unclear. When analyzed, the interaction of iPPOV with porci ne peripheral blood mononuclear cells was seen to involve T helper cells as the main target cell population responding to iPPOV. These cells displayed a strong proliferation, and were the major source for the observed increas ed levels of IL-2. Activation of the T helper cells was MHC class II depend ent, but not MHC class II restricted: cellular processing of iPPOV was not required for presentation by autologous, allogeneic or xenogeneic MHC class II molecules. Furthermore, CD3 and CD4 molecules were involved in the stim ulation, indicating a receptor-mediated activation of T helper cells. The r esults demonstrated typical characteristics of a superantigen-induced respo nse providing evidence for a viral component within PPOV functioning as sup erantigen(s) in swine.