Alloimmunity does not protect from challenge with the feline immunodeficiency virus F. Reggeti, D. Bienzle * Department of Pathobiology, University of Guelph, Guelph, ON N1G 2W1, Canada Received 7 January 2008; received in revised form 27 February 2008; accepted 7 March 2008 Abstract Immune responses against polymorphic host molecules incorporated into lentiviral envelopes during cell budding have induced protection against primate immunodeficiency virus infection. Dendritic cells (DCs) express high levels of MHC molecules and are infectable by lentiviruses. Therefore, in this pilot study we addressed the hypothesis that immunization of cats with allogeneic DC would induce immune responses that protect against challenge with the feline immunodeficiency virus. Two groups of 3 cats each received 3 subcutaneous injections of allogeneic or autologous DC, and were then challenged with viruses propagated in the immunizing DC. Infection status and lymphocyte parameters of cats were assessed during 6 weeks after challenge. MHC II antigens were incorporated into viral particles as identified by Western blot; and antibodies reactive with MHC class II antigens were detected in the serum of cats immunized with allogeneic but not autologous DC. After challenge, all cats had proviral DNA in blood leukocytes from 2 weeks post-challenge onward and seroconverted. Cats immunized with allogeneic DC maintained higher total and CD21 + lymphocyte concentrations, and higher CD4 + /CD8 + lymphocyte ratios; however, these differences were not significantly different from cats that received autologous DC immunizations. Plasma viral load was not significantly different between groups of cats ( p = 0.204). These results suggest that immunization of cats with allogeneic DC does not induce protective immunity against FIV infection. # 2008 Elsevier B.V. All rights reserved. Keywords: Lentivirus; Dendritic cell; Alloimmunization; Cat; Retrovirus 1. Introduction Lentiviruses incorporate host cell membrane anti- gens as they bud from infected cells (Henderson et al., 1987; Hoxie et al., 1987). The lentiviruses that induce immunodeficiency (HIV, SIV and FIV) infect lympho- cytes and cells of the monocyte/macrophage lineage, which express abundant major histocompatiblity (MHC) and other molecules important for cell function and trafficking. Incorporation of these antigens into lentiviral envelopes is neither random nor stable, but dependent on the haplotype of the host, the specific virus strain, and the cell type for virus propagation (Cantin et al., 2001). The density of virion-associated MHC molecules may exceed that of viral envelope proteins (Arthur et al., 1992; Schols et al., 1992). The presence of highly polymorphic MHC class II antigens in the envelope of infecting virions may influence the interaction between the virus and its receptor, the likelihood of viral cell entry, and the nature of signals transmitted to lymphocytes. Furthermore, exposure to MHC antigens on viruses may induce allogeneic immune responses against antigens in new hosts. Such www.elsevier.com/locate/vetimm Available online at www.sciencedirect.com Veterinary Immunology and Immunopathology 124 (2008) 152–162 * Corresponding author. Tel.: +1 519 824 4120x54351; fax: +1 519 824 5930. E-mail address: dbienzle@uoguelph.ca (D. Bienzle). 0165-2427/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2008.03.010