Skin immune responses in cattle after primary and secondary infections with Hypoderma lineatum (Diptera: Oestridae) larvae C. Lo ´pez a, * , D.D. Colwell b , R. Panadero a , A. Paz a , J. Pe ´rez c , P. Morrondo a , P. Dı ´ez a , J.L. Cascallana d , V. Santamarı ´a d , A. Bravo d a Parasitologı ´a y Enfermedades Parasitarias, Facultad de Veterinaria de Lugo, Universidad de Santiago de Compostela, 27071 Lugo, Spain b Agriculture and Agri-Food Canada, Lethbridge Research Centre, Alta., Canada c Anatomı ´a y Anatomı ´a Patolo ´gica Comparada, Facultad de Veterinaria de Co ´rdoba, Spain d Anatomı ´a Patolo ´gica, Facultad de Veterinaria, Universidad de Santiago de Compostela, Lugo, Spain Received 9 November 2004; received in revised form 8 June 2005; accepted 8 June 2005 Abstract Cellular immune responses were examined in the skin of cattle after primary and secondary experimental infections with Hypoderma lineatum larvae. Skin biopsies were taken at 0, 6, 12, 48 and 96 h post-infection (h.p.i.). In primary infected animals the penetration of Hypoderma larvae was characterized by moderate inflammatory responses. The pattern of cellular changes in previously infected animals suggested an allergic or rheumatic process, probably as a consequence of the development of a type III hypersensitivity reaction against the second or successive reinfections. Perivascular infiltration with CD3 + T lymphocytes was marked in infected groups, but especially in previously infected animals, with a significant increase with respect to uninfected controls at 48 h.p.i. B cells remained close to control values during primary infection, while they increased significantly 12 h.p.i. in reinfected animals. IgG + plasma cells were also very abundant during secondary infections, with significant differences from primary infected and uninfected animals from 6 h.p.i. onwards. These results suggest that secondary infections allow cellular responses which may be effective in killing some of the entering larvae, resulting in a degree of resistance. # 2005 Elsevier B.V. All rights reserved. Keywords: Myiasis; Hypoderma lineatum; Skin immune response; Immunohistochemistry; Cattle 1. Introduction Larvae of Hypoderma are obligate parasites that migrate and feed for several months in host’s tissues. Newly hatched larvae penetrate unbroken bovine skin aided by enzymatic secretions produced by their salivary www.elsevier.com/locate/vetimm Veterinary Immunology and Immunopathology 108 (2005) 285–294 * Corresponding author. Tel.: +34 982 252303; fax: +34 982 252195. E-mail address: clopez@lugo.usc.es (C. Lo ´pez). 0165-2427/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2005.06.001