Expression of immune response genes in rainbow trout skin induced by Gyrodactylus derjavini infections Thomas Lindenstrøm a,* , Christopher J. Secombes b , Kurt Buchmann a a Department of Veterinary Microbiology, Section of Fish Diseases, Royal Veterinary and Agricultural University, Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark b Scottish Fish Immunology Research Centre, University of Aberdeen, Scotland, Aberdeen AB24 2TZ, Scotland, UK Received 2 May 2003; received in revised form 26 August 2003; accepted 26 August 2003 Abstract By means of semi-quantitative RT-PCR, expression of a number of immune relevant genes was studied in skin of small rainbow trout Oncorhynchus mykiss (Walbaum, 1792) fry during both primary and secondary infections with the ectoparasitic monogenean Gyrodactylus derjavini Mikailov, 1975. The target genes studied included the cyto- and chemokines TNF-a1, TNF-a2, TGF-b and IL-8, the inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) genes and finally, two cell markers, the b-chains of TCR and MHC II, from the adaptive arm of the immune system. In general, constitutive expression of all studied genes was apparent. Significant increases in expression of the TNF-a1 isoform could be observed at day 8 p.i. in primary infections and although less marked, the a2 isoform of TNF showed a similar trend. With the cytokine TGF-b, 8–10 times increase in the transcription levels was observed in secondary infections compared to uninfected hosts. However, no parasite related changes in expression patterns could be observed for IL-8. Parasite infections elicited strong iNOS expression by 4 days p.i., but significant differences were not detected before day 8 p.i., when transcript levels were increased 5.5–9.6 times compared to uninfected controls. Augmented expression of COX-2 could also be observed in primary, but not secondary, infections at later stages of infections. No clear parasite related changes in transcript levels of the two cell markers TCRb and MHC IIb could be observed. Although the cellular source(s) was not determined, most of the examined factors appear to take part in a local signalling network of pivotal importance for the initiation, orchestration, effectuation and modulation of immune responses in rainbow trout against the ectoparasite G. derjavini. # 2003 Elsevier B.V. All rights reserved. Keywords: Gyrodactylus derjavini; Rainbow trout (Oncorhynchus mykiss); Gene expression; Inflammatory; Immune-relevant; Skin; RT-PCR 1. Introduction Several studies have shown that rainbow trout are capable of controlling and subsequently expel- ling infections with the ectoparasitic monogenean Gyrodactylus derjavini (Buchmann and Uldal, 1997; Lindenstrøm and Buchmann, 1998, 2000). A number of immune parameters have been shown to be involved, as judged from both in vivo and ex vivo assays (Buchmann and Bresciani, 1998, 1999; Buch- mann, 1998a; Lindenstrøm and Buchmann, 2000). However, knowledge on how these reactions are coordinated and orchestrated is still poor and some of the factors suggested to be involved are primarily Veterinary Immunology and Immunopathology 97 (2004) 137–148 * Corresponding author. Tel.: þ45-35-28-27-03; fax: þ45-35-28-27-11. E-mail address: thl@kvl.dk (T. Lindenstrøm). 0165-2427/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2003.08.016