The immunostimulatory properties of inactivated Parapoxvirus
ovis (iPPVO) have long been investigated in different animal
species and experimental settings. In this study, we investigated the effects of
iPPVO on cytokine expression in mice after intraperitoneal inoculation. Spleen
and sera collected from iPPVO-treated mice at intervals after inoculation were
submitted to cytokine mRNA determination by real-time PCR (qPCR), serum protein
concentration by ELISA, and interferon (IFN)-α/β activity by bioassay. The
spleen of iPPVO-treated animals showed a significant increase in mRNA expression
of all cytokines assayed, with different kinetics and magnitude. Proinflammatory
cytokines interleukin (IL)-1β, tumor necrosis factor-alpha (TNF-α), and IL-8
mRNA peaked at 24 hours postinoculation (hpi; 5.4-fold increase) and 48 hpi (3-
and 10-fold increases), respectively. A 15-fold increase in IFN-γ and 6-fold
IL-12 mRNA increase were detected at 48 and 24 hpi, respectively. Increased
expression of autoregulatory cytokines (Th2), mainly IL-10 and IL-4, could be
detected at later times (72 and 96 hpi) with peaks of 4.7- and 4.9-fold
increases, respectively. IFN-I antiviral activity against encephalomyocarditis
virus was demonstrated in sera of treated animals between 6 and 12 hpi, with a
>90% reduction in the number of plaques. Measurement of serum proteins by
ELISA revealed increased levels of IL-1, TNF-α, IL-12, IFN-γ, and IL-10, with
kinetics similar to those observed by qPCR, especially for IL-12 and IFN-γ.
These data demonstrate that iPPVO induced a transient and complex cytokine
response, initially represented by Th1-related cytokines followed by
autoregulatory and Th2 cytokines.