ARTICLE IN PRESS Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/dci Antimicrobial peptides derived from hemoglobin are expressed in epithelium of channel catfish (Ictalurus punctatus, Rafinesque) Anirudh J. Ullal a,1 , R. Wayne Litaker b , Edward J. Noga a, a Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606, USA b Center for Coastal Fisheries and Habitat Research, NOAA National Ocean Service, 101 Pivers Island Road, Beaufort, NC 28516-9722, USA Received 12 March 2008; received in revised form 11 April 2008; accepted 13 April 2008 Available online 15 May 2008 KEYWORDS Innate immunity; Extra-erythrocytic; Hemoglobin; Stage-specific activity; Ichthyophthirius multifiliis Summary The b-chain of the respiratory protein hemoglobin (Hbb), has recently been identified in novel sites, including mammalian macrophages and alveolar epithelium, as well as in gill microsomes of fish. However, the functional significance of extra-erythrocytically expressed hemoglobin has been unclear. Here we show inducible expression and upregulation of antimicrobial peptides (AMPs) homologous to Hbb in the gill epithelium of channel catfish (Ictalurus punctatus) in response to parasitic (Ichthyophthirius multifiliis, ich) infection. One peptide (HbbP-1), while having activity against some fish bacterial pathogens (e.g., Aeromonas hydrophila), had especially potent antiparasitic activity that was specifically lethal (lytic) to the feeding (trophont) stage of ich and also appeared to accelerate the differentiation of trophonts. However, it had no apparent effect on either the disseminative (theront) or reproductive (tomont) stages, nor was it lytic to channel catfish erythrocytes. Fish experimentally challenged with ich confirmed that the HbbP-1 sequence was both transcribed and translated in skin and gill epithelium, the target tissues for ich. The Hb AMP concentration expressed in vivo appeared to be well within the antiparasitic concentrations measured in vitro. Our findings suggest that hemoglobin-derived AMPs might play a significant role in the non-specific immune response. & 2008 Elsevier Ltd. All rights reserved. 0145-305X/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.dci.2008.04.005 Abbreviations: AMP, antimicrobial peptide; Hb, hemoglobin; Hbb, hemoglobin b; HbbP-1, -2, -3, hemoglobin b peptides -1, -2, -3; CAU-PAGE, continuous acid-urea polyacrylamide gel electrophoresis; HLP, histone-like protein. Corresponding author. Tel.: +1 919 513 6236; fax: +1 919 513 6336. E-mail address: ed_noga@ncsu.edu (E.J. Noga). 1 Present address: Division of Rheumatology, Department of Medicine, Duke University Medical Center, 508 Fulton Street, Durham, NC 27705, USA. Developmental and Comparative Immunology (2008) 32, 1301–1312