The feline immunodeficiency virus (FIV) model provides a system to study lentivirus transmission, virus kinetics, pathogenesis, host responses, and immune dysfunction in a natural, out-bred host, under controlled conditions with specific-pathogen-free animals. The diversity of primary FIV strains can be exploited to mirror the range of disease manifestations associated with HIV infection. FIV is infectious via intravenous, intraperitoneal, intradermal, or subcutaneous injection as well as by atraumatic instillation onto the oral, vaginal, or rectal mucosa. Together, these features allow investigators to model specific aspects of HIV infection in a highly relevant and relatively inexpensive animal model. Well-developed areas of the FIV model include: (1) transmission of cell-associated as well as cell-free virus; (2) mucosal infectivity and immunopathogenesis; (3) vertical transmission; (4) acquired immunodeficiency including defects of the innate immune system; (5) thymic dysfunction; (6) neurotropism and neuropathogenesis; (7) host-virus interactions and the role of specific gene products; (8) efficacy of antiviral therapy; and (9) efficacy and immune correlates of experimental vaccines. This review will encompass areas specific to transmission and immunopathogenesis.

Feline infectious peritonitis virus (FIPV) is a coronavirus that causes sporadic fatal disease in cats characterized by vasculitis, granulomatous inflammation and effusive pleuritis/peritonitis. Histologic changes in lymphoid tissues include lymphoid hyperplasia, lymphoid depletion, histiocytosis, and granuloma formation. Although viremia occurs, histologic lesions are not found uniformly throughout lymphoid tissues. We used experimental infection of cats with a highly pathogenic FIPV isolate, UCD8, to study histologic lesions, virus replication, and cytokine expression in multiple lymphoid tissues during the effusive phase of disease. Viral RNA was found in 76% of central tissues (mediastinal lymph node, spleen, mesenteric lymph node) examined, as compared to 27% of peripheral tissues (popliteal lymph node, cervical lymph node, femoral bone marrow). All tissues positive for virus replication also demonstrated lymphoid depletion. Generally, affected tissues had lower levels of IL-4 and IL-12-p40 mRNA and higher levels of IL-10 mRNA. Although no differences in IFN-gamma or TNF-alpha mRNA were measured, TNF-alpha protein expression was greater in affected tissues and demonstrated a shift in the source of TNF-alpha from macrophages to lymphocytes. Together, these results colocalize FIPV replication, lymphocyte depletion in tissues, and alterations in cytokine transcription and translation. A possible role for TNF-alpha in the previously described FIPV-induced lymphocyte apoptosis is also suggested.

The objectives of the present study were to characterize and compare the repertoire of cytokine-genes transcribed in skin homogenates obtained from normal dogs and dogs with atopic dermatitis (AD) using a reverse-transcriptase polymerase chain reaction and canine-specific cytokine-gene primers. Whereas IL-4 and IL-5 cytokine-gene transcripts were detected more commonly in atopic skin biopsy homogenates, IL-2 mRNA was amplified more often from normal control specimens. IFN-gamma mRNA was detected in 5/29 atopic specimens, 4 of them obtained from the only dog with chronic skin lesions. One-fourth of atopic samples exhibited clear type-2 cytokine profiles; the remainder did not demonstrate polarized repertoires. Conversely, type-1 cytokine profiles were characterized in one-fourth of normal control specimens. The present study establishes, for the first time, the transcription of type-2 cytokine-genes in the skin of dogs with AD. Future experiments investigating the cellular origin and dynamics of allergic cytokine-gene transcription are needed to confirm whether or not canine AD could be considered an immunological model for a human disease.

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Display of heterologous antigens on the cell surface is considered a useful technique for vaccine delivery by recombinant lactobacilli. In this study, two recombinant Lactobacillus acidophilus derivatives displaying Salmonella flagellin (FliC) were constructed using different anchor motifs. In one instance, the FliC protein was fused to the C-terminal region of a cell envelope proteinase (PrtP) and was bound to the cell wall by electrostatic bonds. In the other case, the same antigen was conjugated to the anchor region of mucus binding protein (Mub) and was covalently associated with the cell wall by an LPXTG motif. These two recombinant L. acidophilus cell surface displays resulted in dissimilar maturation and cytokine production by human myeloid dendritic cells. The surface-associated antigen was highly sensitive to simulated gastric and small intestinal juices. By supplementation with bicarbonate buffer and soybean trypsin inhibitor, the cell surface antigen was protected from proteolytic enzymes during gastric challenge in vitro. The protective reagents also increased the viability of the L. acidophilus cells upon challenge with simulated digestive juices. These results demonstrate the importance of protecting cells and their surface-associated antigens during oral immunization.