TNF and parasitic infectious disease: The apparent lack of a pro-inflammatory response to T, bryosalmonae at the transcriptional level is particularly intriguing given that fish bacterial and other parasitic infections exhibit, to some extent, concomitant up-regulation of pro-inflammatory (TNF-α, IL-1β, IL-8) and anti-inflammatory (IL-6, IL-10, IL-11, nIL-1F) cytokines [13-15].