Abstract

Morbilliviruses can cause severe epidemics not only in pinnipeds.^1-3 Secondary infections due to a marked immunosuppression, similar to a canine distemper virus (CDV) infection in dogs or measles in humans, have been discussed as a major cause of high morbidity and mortality rates associated with acute morbillivirus outbreaks.^4-6 To delve into the pathogenesis of a CDV-induced immunosuppression in juvenile harbour seals concanavalin A (Con A)-stimulated and non-stimulated phocine lymphocytes were infected in vitro with an attenuated canine morbillivirus (Ond-CDV). The gene expression of interleukin (IL)-6, IL-12 and tumor necrosis factor-α (TNFα) as pro-inflammatory and IL-4, IL-10 and transforming growth factor-β (TGFβ) as anti-inflammatory cytokines was investigated using real-time quantitative reverse transcription polymerase chain reaction. In stimulated cells, virus was added either after a Con A-incubation period of 48 hours or at the same time as the mitogen. The in vitro CDV-infection of phocine lymphocytes caused an initial increase of pro-inflammatory cytokines 24 hours post infection (p.i.), followed by a decrease in gene expression after 48 hours. Contemporaneously, a strong increase in the expression of IL-4 and TGFβ as anti-inflammatory cytokines was detectable 48 hours p.i. An increased IL-10 production in phocine lymphocytes was only detectable when stimulation and infection were conducted at the same time. Without stimulation and in cells stimulated for 48 hours prior to virus infection, decreased amounts of IL-10-mRNA-transcripts were found. It could be shown that the specific time of stimulation has an important influence on gene expression of the investigated cytokines. This study served to shed light on the Ond-CDV-induced changes in the expression of cytokines and their dependency on different statuses of cell-activation. This is a major contribution to the understanding of the development of morbillivirus-associated immunosuppression in harbour seals.

References

1.  Heide-Jørgensen MP, Härkönen T, Dietz R, Thompson P 1992. Retrospective of the 1988 European seal epizootic. Dis Aquat Org 13: 37-62.

2.  Osterhaus ADME, De Swart RL, Vos HW, Ross PS, Kenter MJH, Barret T 1995. Morbillivirus infections of aquatic mammals: newly identified members of the genus. Vet Microbiol 44:219-227.

3.  Müller G, Wohlsein P, Beinecke A, Haas L, Greiser-Wilke I, Siebert U, Fonfara S, Harder T, Stede M, Gruber AD, Baumgärtner W 2004. Phocine distemper in German seals. Emerg Infec Dis 10:723-725.

4.  Beineke A, Markus S, Borlack J, Thum T, Baumgärtner W 2008. Increase of pro-inflammatory cytokine expression in non-demyelinating early cerebral lesions in nervous canine distemper. Viral Imm 21:401-410.

5.  Karp CLM, Wysocka M, Wahl IM, Ahearn JM, Cuomo PJ, Sherry B, Trinchieri G, Griffin DE 1996. Mechanism of suppression of cell-mediated immunity by measles virus. Science 273:228.

6.  Moss WJ, Ota MO, Griffin DE 2004. Measles: immune suppression and immune responses. Int J Biochem Cell Biol 36:1380-1385.