Cloning of feline FOXP3 and detection of expression in CD4+CD25+ regulatory T cells

Regulatory T cells (Treg) are increased and directly infected by feline immunodeficiency virus (FIV) and likely play a role in other feline autoimmune, neoplastic, and infectious diseases. Phenotypically, Treg are best characterized by surface expression of CD4 and CD25 and intranuclear expression of the forkhead transcription factor Foxp3. Our objective was to clone and sequence feline FOXP3 for the purpose of developing assays to enhance studies of feline Treg. We determined the feline FOXP3 is 1293 nucleotides in length and codes for a protein that shares high homology to other species. A splice variant devoid of exon 2 was also identified. A real-time PCR assay was developed and used to show Foxp3 mRNA expression occurs primarily in CD4+CD25+ T cells. Two cross-reacting antibodies were identified by immunocytochemical staining of HEK293 cells transfected with feline FOXP3. The antibody labeling confirmed the nuclear localization of the protein. A flow cytometric assay was also validated and used to correlate the phenotypic and functional characteristics of feline Treg induced by treatment of lymph node lymphocytes with flagellin or LPS in combination with mitogen or IL2. Together, these studies provide useful tools to further investigate Foxp3 and Tregs in cats.

Failure of TLR4-driven NF-kappa B activation to stimulate virus replication in models of HIV type 1 activation

The interaction of HIV-1 with Toll-like receptors (TLR) on host target cells is incompletely understood. Data from several in vivo and in vitro model systems suggest that TLR2, TLR4, and TLR9 remain functional and if stimulated, cause an upregulation of viral replication. In the present studies employing two different chronically HIV-1-infected cell lines and highly purified TLR agonists, we found ligation of TLR2 and TLR9, but not TLR4, resulted in significant upregulation of HIV-1 production. This result was not due to a lack of TLR4 expression or impaired NF-kappa B activation. Using HEK293 cells transfected with individual TLRs and an HIV-1 LTR reporter confirmed that TLR4 signaling does not directly activate the HIV-1 LTR. Finally, ultrapurified LPS did not enhance production of IL-1 beta or IL-6 in chronically infected U1 cells, whereas significant cytokine production was observed in uninfected U937 cells. These results confirm the biological activity of ultrapurified LPS and raise the possibility that TLR4 signaling pathways may be altered during chronic HIV-1 infection. Collectively, these studies suggest that although several TLR can upregulate NF-kappaB in HIV-1-infected cells, upregulation of NF-kappaB alone is insufficient to activate the viral LTR. Further dissection of the TLR signaling pathways is necessary to determine how TLR stimulation leads to LTR activation and whether HIV-1 infection can alter signaling through TLR4.

In vivo depletion of CD4+CD25+ regulatory T cells in cats

To establish a characterized model of regulatory T cell (Treg) depletion in the cat we assessed the kinetics of depletion and rebound in peripheral and central lymphoid compartments after treatment with anti-CD25 antibody as determined by cell surface markers and FOXP3 mRNA expression. An 82% decrease in circulating CD4+CD25+ Tregs was observed by day 11 after treatment. CD4+CD25+ cells were also reduced in the thymus (69%), secondary lymphoid tissues (66%), and gut (67%). Although CD4+CD25+ cells rebound by day 35 post-treatment, FOXP3 levels remain depressed suggesting anti-CD25 antibody treatment has a sustainable diminutive effect on the Treg population. To determine whether CD25+ Treg depletion strategies also deplete activated CD25+ effector cells, cats were immunized with feline immunodeficiency virus (FIV) p24-GST recombinant protein, allowing them to develop a measurable memory response, prior to depletion with anti-CD25 antibody. Anti-FIV p24-GST effector cell activity in peripheral blood after depletion was sustained as determined by antigen-specific T cell proliferation and humoral responses against FIV p24-GST with an ELISA for antigen-specific feline IgG. Furthermore, development of an anti-mouse response in Treg-depleted cats was similar to control levels indicating the retained capacity to respond to a novel antigen. We conclude that despite alterations in CD25+ cell levels during depletion, the feline immune system remains functional. We demonstrate here a model for the study of disease pathogenesis in the context of reduced numbers of immunosuppressive CD4+CD25+ Tregs throughout the feline immune system.

Phagocytic plasmacytoma in a dog

A 4-year-old neutered male Golden Retriever was presented to the oncology service of the North Carolina State University Veterinary Teaching Hospital for staging of a histiocytic sarcoma of the left forelimb, diagnosed on the basis of biopsies submitted by the referring veterinarian. Cytologic assessment of aspirates of 2 splenic nodules identified on ultrasonographic examination of the abdomen revealed a highly phagocytic population of neoplastic round cells morphologically suggestive of plasma cells. Histologic assessment of the forelimb mass after amputation of the limb revealed a neoplastic round cell population demonstrating extensive cytophagia and erythrophagia. Immunohistochemical analysis of the tumor population revealed it to be negative for BLA.36 with sporadic positivity for lysozyme and CD79a. Immunofluorescent evaluation revealed weak tumor cell positivity for immunoglobulin (Ig) A and IgM, but extensive strong positivity for IgG, confirming the plasma cell origin of the tumor. Although extensive phagocytic activity may strongly suggest histiocytic origin, plasma cell origin must also be considered among the differential diagnoses for phagocytic round cell tumors.

Vaccination of cats with attenuated feline immunodeficiency virus proviral DNA vaccine expressing gamma interferon

A feline immunodeficiency virus (FIV) provirus with a vif gene deletion (FIVDelta vifATGgamma) that coexpresses feline gamma interferon (IFN-gamma) was tested as a proviral DNA vaccine to extend previous studies showing efficacy with an FIV-pPPRDelta vif DNA vaccine. Cats were vaccinated with either FIVDelta vifATGgamma or FIV-pPPRDelta vif proviral plasmid DNA or with both FIV-pPPRDelta vif DNA and a feline IFN-gamma expression plasmid (pCDNA-IFNgamma). A higher frequency of FIV-specific T-cell proliferation responses was observed in cats immunized with either FIVDelta vifATGgamma or FIV-pPPRDelta vif plus pCDNA-IFNgamma, while virus-specific cytotoxic-T-lymphocyte responses were comparable between vaccine groups. Antiviral antibodies were not observed postvaccination. Virus-specific cellular and humoral responses were similar between vaccine groups after challenge with a biological FIV isolate (FIV-PPR) at 13 weeks postimmunization. All vaccinated and unvaccinated cats were infected after FIV-PPR challenge and exhibited similar plasma virus loads. Accordingly, inclusion of plasmids containing IFN-gamma did not enhance the efficacy of FIV-pPPRDelta vif DNA immunization. Interestingly, the lack of protection associated with FIV-pPPRDelta vif DNA immunization contrasted with findings from a previous study and suggested that multiple factors, including timing of FIV-pPPRDelta vif inoculations and challenge, as well as route of challenge virus delivery, may significantly impact vaccine efficacy.

Cytokine Modulation of the Innate Immune Response in Feline Immunodeficiency Virus–Infected Cats

BACKGROUND

In vitro data suggest that innate immune function in human immunodeficiency virus type 1-infected patients is compromised; however, in vivo studies are lacking. Feline immunodeficiency virus (FIV) infection in cats provides an excellent model to explore innate immune function in vivo. The innate response against Listeria monocytogenes is well understood, making it a useful immune probe.

METHODS

Recombinant L. monocytogenes carrying eukaryotic expression plasmids for feline tumor necrosis factor (TNF)- alpha , interleukin (IL)-10, interferon (IFN)- gamma , and IL-15 were created to determine whether specific cytokines would modulate innate immune function. L. monocytogenes was delivered subcutaneously, and local lymph nodes were evaluated for size, cell subpopulations, and L. monocytogenes burden. Two months later, memory responses were evaluated by IFN- gamma enzyme-linked immunospot assay.

RESULTS

FIV-positive cats had significantly less lymph-node enlargement and a greater L. monocytogenes burden than FIV-negative control cats. TNF- alpha improved listericidal activity in FIV-negative control cats but not in FIV-positive cats, whereas IL-10 modestly reduced function in FIV-negative control cats. IFN- gamma improved memory responses but not clearance of L. monocytogenes. IL-15 improved innate function in FIV-positive cats and increased the percentage of natural killer cells.

CONCLUSIONS

Lentivirus infection impairs innate immune function in vivo, and IL-15 can significantly restore function. We hypothesize that altered dendritic-cell function and increased regulatory T cell activity may underlie the innate immune defect in HIV infection.

Desmoglein-1 is a minor autoantigen in dogs with pemphigus foliaceus

The majority of human patients with pemphigus foliaceus (PF) have circulating IgG autoantibodies that target conformational epitopes on the desmosomal cadherin desmoglein-1 (dsg1). Limited studies using immunoblot techniques suggested that the principal autoantigen in dogs with PF might also be dsg1. It was the objective of this study to test this hypothesis. A comprehensive survey of canine PF sera was conducted using a novel screening strategy that detects conformational epitopes. This method consists of the ectopic expression of canine dsg1 at the surface of human 293T epithelial kidney cells and their live screening, i.e. prior to fixation. Out of seven control human PF sera that bound to canine epidermis, three (57%) contained IgG autoantibodies that recognized ectopically expressed canine dsg1 with a membrane and punctate pattern. Out of 83 canine PF sera only five (6%) contained IgG that recognized canine dsg1. Consistent with findings for human PF sera obtained in this study, autoantibody binding was conformation- and glycosylation-dependent as demonstrated by calcium chelation with EDTA and tunicamycin or wheat germ agglutinin treatment, respectively. In conclusion, these studies establish canine dsg1 as a minor autoantigen for canine PF. Antigenic epitopes appear to be conformation- and glycosylation-dependent.

Pre-existing immunity to pathogenic Listeria monocytogenes does not prevent induction of immune responses to feline immunodeficiency virus by a novel recombinant Listeria monocytogenes vaccine

Listeria monocytogenes is an attractive biologic vaccine vector against HIV because it induces a strong cell mediated immune response, can be delivered by mucosal routes, can be readily manipulated to express viral antigens, and is easy and inexpensive to produce. Proof of concept studies have been performed using HIV Gag expressing recombinant L. monocytogenes in the mouse. Here we report the development and validation of recombinant L. monocytogenes to be evaluated in the FIV/cat model of HIV. Using a simplified approach to introduce individual and polyprotein FIV gag genes, we show that recombinant L. monocytogenes containing the entire gag expresses the full-length Gag polyprotein in a soluble secreted form. A DNA vaccine plasmid (pND14-Lc-env) that replicates in Gram positive bacteria and contains the FIV SU (gp100) and the ectodomain of TM (gp40) in a eukaryotic expression cassette was transfected into LM-gag to create LM-gag/pND14-Lc-env. After infection of target cells with LM-gag/pND14-Lc-env in vitro, both FIV Gag and Env proteins were detected in soluble cell lysates. Whether previous exposure to L. monocytogenes affects the immunogenicity of LM-gag/pND14-Lc-env was determined in cats infected with wild-type L. monocytogenes orally and/or subcutaneously. After a single oral dose of LM-gag/pND14-Lc-env, cats with existing anti-L. monocytogenes immune responses developed anti-FIV Gag IgA titers in vaginal secretions, saliva, and feces. Similarly, FIV Gag and Env specific IFN-gamma ELISPOT responses were measurable in spleen and lymph node but at a statistically higher frequency in cats exposed to a single subcutaneous dose of wild-type L. monocytogenes versus cats exposed both subcutaneously and orally. The FIV/cat model will provide a useful challenge system to determine whether recombinant L. monocytogenes can protect against a lentivirus in its natural host after challenge by the routes common to HIV transmission.

Toll-like receptor expression in feline lymphoid tissues

Toll-like receptors (TLRs) are germline-encoded pattern recognition receptors (PRRs) that activate the innate immune system. While it is clear that TLRs are important in the immune response against pathogens, they may also be exploited by some pathogens. Our objective is to determine whether feline immunodeficiency virus (FIV) infection affects TLR expression or function thereby resulting in innate immune dysfunction. To this end, we cloned partial sequences for feline TLRs 1--3, 5--8, and developed real-time PCR assays to quantify feline TLRs 1--9. TLR expression was quantified in normal cat lymphoid tissues, purified lymphocyte subsets, and FIV-infected cell lines. Different expression patterns of TLRs were found in spleen, mesenteric lymph node, retropharyngeal lymph node, thymus, intestinal intraepithelial lymphocytes, and lamina propria lymphocytes. B lymphocytes, CD4+ T cells, and CD8+ T cells all expressed TLRs 2--5, 7--9; however, the relative levels of expression varied among lymphocyte phenotypes. Infection of cell lines with FIV resulted in altered TLR expression levels that differed depending on cell type. These results demonstrate that tissue distribution of TLRs is associated with the immunological role of a particular tissue, that lymphocytes may also express these 'innate immune' receptors, and that FIV infection can alter TLR expression.

Methodology for isolation and phenotypic characterization of feline small intestinal leukocytes

Critical assessment of intestinal immune responses requires the ability to characterize leukocytes from different anatomic locations as leukocytes from inductive sites such as Peyer's patches and lymphoid follicles vary significantly from their effector counterparts, intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL). This study describes (1) methods developed to isolate specific intestinal leukocyte populations with high yield and purity, (2) difficulties encountered in establishing a panel of monoclonal antibodies to assess phenotype, and (3) the phenotypic characterization of effector and inductive sites in the feline small intestine. We found that the phenotypic distribution of feline intestinal leukocytes was similar to that found in other species such as humans, macaques and mice. The majority of IEL were CD5(+) T-cells with less than 7% B-cells. CD8(+) T-cells comprised approximately 60% of the IEL with roughly half displaying CD8alphaalpha homodimers. Approximately 10% of IEL were CD4(+) T-cells. In the LPL, CD4(+) T-cells predominated at 42%, with 33% CD8(+) T-cells and 10% B-cells. As would be expected, B-cells predominated in Peyer's patches with 40% B-cells, 28% CD4(+) T-cells and 20% CD8(+) T-cells. Increased MHCII expression was found in the Peyer's patches as compared to the IEL and LPL. B7.1 expression was significantly higher in mucosal leukocyte populations as compared to organized lymphoid tissue in the periphery with expression detected on 65% of IEL and 53% of LPL. Plasma cells were found in all regions of small intestine examined with greater numbers in lamina propria and Peyer's patches. Lymphoblasts were only identified in inductive tissue. In general, no differences were found between the phenotype of mucosal leukocyte populations from specific pathogen free or random source cats. However, the percentage of CD4(+) CD25(+) T-cells was significantly greater in both IEL and LPL from random source animals. This study provides techniques and a baseline from which future studies of the feline intestinal immune system can be conducted.

Feline cytokine ELISPOT: issues in assay development

The enzyme-linked immunospot (ELISPOT) assay is a sensitive and relatively simple assay for detecting secreted cellular products such as cytokines and has become an invaluable immunological tool. The ELISPOT has been used extensively in human and murine research but has only recently been used to assess the feline immune system. For researchers studying feline disease or using the cat as a model of human disease, the quantification of cytokine-producing cells by ELISPOT is an invaluable technique for investigations of disease immunopathogenesis and vaccine efficacy. For example, use of the interferon (IFN)-gamma ELISPOT to measure the frequency of antigen-specific T-cells during feline immunodeficiency virus (FIV) infection or after immunization with candidate FIV vaccines is of particular interest. This application of the ELISPOT may serve to expand the utility of FIV as a model for human immunodeficiency virus. Broader applications of the ELISPOT should further our understanding of feline diseases and be useful in the rational development of more efficacious vaccines and therapeutic modalities for the enhancement of feline health. This chapter discusses important parameters of ELISPOT design that will enable researchers to develop and analyze the feline-specific assays within their own laboratory.

Cloning and expression of feline interleukin 15

A cDNA encoding feline interleukin 15 (IL15) was cloned from the lymph node of a cat infected with feline infectious peritonitis virus. The cDNA is 486 bp in length and encodes a protein of 162 amino acids. Recombinant protein was readily expressed as a GST fusion in Escherichia coli and purified by glutathione affinity chromatography. Expression of recombinant protein in mammalian cells was only accomplished by eliminating the 5' and 3' UTR, replacing the IL15 signal peptide with the tissue plasminogen activator signal peptide, and adding 3' sequence to disrupt presumptive secondary structure of the mRNA. Biologically active feline IL15 was expressed in HEK293T cells and was shown to sustain primary feline lymphocytes, a feline T cell line, and mouse CTLL-2 cells. Proliferation of CTLL-2 cells was induced by the recombinant protein in a dose-dependent manner. Monoclonal and polyclonal antibodies against human IL15 recognized feline IL15 in immunofluorescence and Western blot assays. Additionally, feline IL15 was detectable using a commercially available human IL15 ELISA kit.

Assessment of CD4+ and CD8+ IFN-gamma producing cells by ELISPOT in naïve and FIV-infected cats

IFN-gamma is critical for the development of antiviral cell-mediated immunity in HIV infected humans and FIV infected cats. The ELISPOT has proven to be a technically straightforward assay to quantify the number of IFN-gamma producing cells and offers a reasonable alternative for the quantitative measurement of T-cell function in cats. We used a feline-specific ELISPOT to identify constitutive as well as Con A stimulated IFN-gamma production in T-cell subsets and determine if there were differences between purified (positively sorted) and negatively depleted populations from naïve and FIV infected cats. We found no difference in the total number of PBMC constitutively producing IFN-gamma in naïve and FIV+ cats. Con A exposure was associated with increased numbers of IFN-gamma producing PBMC in naïve, but not FIV+, cats. Equivalent numbers of CD4+ and CD8+ T cells constitutively expressed IFN-gamma in naïve cats. However, in FIV+ cats, the number of IFN-gamma producing CD8+ T-cells was approximately two-fold over that seen for CD4+ T-cells. We found minimal differences between purified (e.g. CD4+ or CD8+) and corresponding depleted (e.g. CD8- or CD4-) populations in samples from FIV+ cats. In contrast, depleted populations from naïve cats showed greater response to Con A than did purified populations. Thus, while determination of the number of IFN-gamma producing cells by feline-specific ELISPOT is a useful tool for the evaluation of the feline immune response, determination of the initial sample population and T-cell subset is critical for optimal interpretation of the IFN-gamma ELISPOT.

Peptide mapping of feline immunodeficiency virus by IFN-gamma ELISPOT

Interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) has become an important tool in studying antigen-specific T lymphocyte responses. Soluble peptides can be used to map T-cell epitopes, providing information that is useful in the design and evaluation of vaccines as well as studies of immunopathogenesis. To date, this assay has not been widely utilized in feline immunodeficiency virus (FIV) research. We have developed a feline IFN-gamma ELISPOT assay and used it to determine FIV-specific T-cell epitopes recognized by infected cats. A panel of 331 peptides, 15 amino acids in length and overlapping by 10 residues was synthesized. The peptide library spanned the FIV structural (Gag), envelope (Env), reverse transcriptase (RT), and open-reading-frame A (OrfA) proteins. Initially, 34 pools, containing 7-10 peptides each were screened by IFN-gamma ELISPOT against peripheral blood mononuclear cells (PBMC) from eight cats chronically infected with the NCSU(1) molecular clone of FIV and four uninfected control cats. Individual peptides from pools recognized by FIV+ cats were then evaluated and optimal peptides were combined into pools representing Gag, Env, RT, and OrfA. A higher percentage of FIV infected cats were identified as responders against the peptide pools when using fresh PBMC as compared to cryopreserved PBMC. In vitro restimulation of cryopreserved PBMC with the peptide pools improved the sensitivity of the assay to similar levels as observed from fresh samples. Individual peptides used in the pools were generally found to stimulate CD8+ T-cells more efficiently than CD4+ T-cells. Comparison of the peptide sequences to representative FIV sequences from clades A-D showed conservation was high among Gag and RT peptides, variable among Env peptides and low for OrfA peptides. The IFN-gamma ELISPOT assay and FIV-specific peptide pools we describe here will be useful in assessing cell-mediated responses to experimental FIV vaccines.

Oral immunization with recombinant listeria monocytogenes controls virus load after vaginal challenge with feline immunodeficiency virus

Recombinant Listeria monocytogenes has many attractive characteristics as a vaccine vector against human immunodeficiency virus (HIV). Wild-type and attenuated Listeria strains expressing HIV Gag have been shown to induce long-lived mucosal and systemic T-cell responses in mice. Using the feline immunodeficiency virus (FIV) model of HIV we evaluated recombinant L. monocytogenes in a challenge system. Five cats were immunized with recombinant L. monocytogenes that expresses the FIV Gag and delivers an FIV Env-expressing DNA vaccine (LMgag/pND14-Lc-env). Control cats were either sham immunized or immunized with wild-type L. monocytogenes (LM-wt). At 1 year after vaginal challenge, provirus could not be detected in any of the nine tissues evaluated from cats immunized with the recombinant bacteria but was detected in at least one tissue in 8 of 10 control animals. Virus was isolated from bone marrow of four of five LMgag/pND14-Lc-env-immunized cats by use of a stringent coculture system but required CD8(+) T-cell depletion, indicating CD8(+) T-cell suppression of virus replication. Control animals had an inverted CD4:CD8 ratio in mesenteric lymph node and were depleted of both CD4(+) and CD8(+) intestinal epithelial T cells, while LMgag/pND14-Lc-env-immunized animals showed no such abnormalities. Vaginal FIV-specific immunoglobulin A was present at high titer in three LMgag/pND14-Lc-env-immunized cats before challenge and in all five at 1 year postchallenge. This study demonstrates that recombinant L. monocytogenes conferred some control of viral load after vaginal challenge with FIV.

Transmission and immunopathogenesis of FIV in cats as a model for HIV

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.

In vivo cytokine response to experimental feline infectious peritonitis virus infection

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-γ or TNF-α mRNA were measured, TNF-α protein expression was greater in affected tissues and demonstrated a shift in the source of TNF-α 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-α in the previously described FIPV-induced lymphocyte apoptosis is also suggested.

A randomized controlled trial of misoprostol monotherapy for canine atopic dermatitis: effects on dermal cellularity and cutaneous tumour necrosis factor-alpha

In this blinded randomized placebo-controlled trial, 20 dogs with atopic dermatitis (AD) were given placebo (8 dogs) or misoprostol (12 dogs) at 5 micro g kg-1, orally, three times daily for 3 weeks. Administration of the active drug, but not of placebo, led to a significant decrease in lesional and pruritus scores. The median reduction from baseline of both scores was approximately 30%. Misoprostol therapy did not lead to decreases of dermal cell counts or skin tumour necrosis factor (TNF)alpha mRNA copy numbers that were significantly different from those of placebo. Skin TNFalpha protein production, assessed using indirect immunofluorescence, decreased or remained unchanged in dogs receiving misoprostol. In contrast, post treatment TNFalpha fluorescence scores were higher in all but two dogs given placebo. The changes from baseline of TNFalpha fluorescence scores did not correlate significantly with those of lesional or pruritus indices. These observations confirm the modest efficacy of misoprostol for treatment of canine AD and suggest that its mild anti-allergic effects are not associated with either inhibition of inflammatory cell emigration or TNFalpha production.

Evaluation of FIV protein-expressing VEE-replicon vaccine vectors in cats

Venezuelan equine encephalitis (VEE) virus-replicon particles (VRP) were used to generate feline immunodeficiency virus (FIV) Gag- and ENV-expressing vaccine vectors. Serum and mucosal FIV-specific antibody was detected in cats immunized subcutaneously, once monthly for 5 months, with FIV-expressing VRP. Expansion of the CD8+ L-selectin negative phenotype and transient CD8+ noncytolytic suppressor activity were seen in cats immunized with FIV-expressing or control VRP. Despite induction of FIV-specific immune responses and nonspecific suppressor responses, all cats became infected following vaginal challenge with high dose, pathogenic cell-associated FIV-NCSU(1) although relative early maintenance of CD4+ cells was seen in FIV-immunized cats.

Interleukin 4-producing CD4+ T cells in the skin of cats with allergic dermatitis

Lesional skin of cats with allergic dermatitis has a cellular infiltrate and a CD4/CD8 ratio comparable to that in humans with atopic dermatitis. CD4+ helper T cells and in particular cells belonging to the Th2 subset play an important role in disease pathogenesis in humans. We investigated the cytokine pattern of CD4+ T cells in situ, with special emphasis on the putative presence of cells producing interleukin 4 (IL4), in cats with allergic dermatitis. Immunohistochemical procedures were used to determine that CD4+ T cells in lesional and nonlesional skin of cats with allergic dermatitis can produce IL4, as occurs in humans. Lesional and nonlesional skin of cats with allergic dermatitis had significantly more IL4+ T cells (P = 0.001) than did skin of healthy control cats. Double staining indicated that all IL4+ cells were positive for pan-T or CD4 markers. Double labeling for mast cell chymase and IL4 stained primarily different cells. Western blotting demonstrated cross-reactivity between the antibody against human IL4 and a feline recombinant IL4. These results indicate that IL4 is primarily produced by CD4+ T cells and is also present in clinically uninvolved skin, indicating a role in the pathogenesis of allergic dermatitis in cats.

Protective immunity against feline immunodeficiency virus induced by inoculation with vif-deleted proviral DNA

To determine whether live-attenuated feline immunodeficiency virus (FIV) proviral DNA will induce protective immunity, a plasmid clone constructed with a FIV provirus containing a deletion in the viral accessory gene vif (FIV-pPPR-Deltavif) was inoculated as proviral DNA into four cats by the intramuscular route. After 43 weeks, these cats were boosted with the same proviral plasmid. Analysis of peripheral blood mononuclear cells at several time points after the primary and booster inoculations revealed no detectable virus or proviral DNA. At 6 weeks after the booster, immunized cats and additional naive control cats were challenged with a cell-free preparation of the infectious biological isolate FIV-PPR by the intraperitoneal route. Virus was detected after challenge in unvaccinated control cats but not in any of the FIV-pPPR-Deltavif-immunized cats. Both FIV Gag- and Env-specific cytotoxic T lymphocyte (CTL) activities were detected in peripheral blood cells of control cats after challenge infection, whereas only one of four cats immunized with FIV-pPPR-Deltavif DNA exhibited a measurable CTL response to Env following challenge. Although anti-Gag antibodies were not detected after both proviral DNA inoculation and challenge, anti-Env antibodies were found in FIV-pPPR-Deltavif-immunized cats after vaccination as well as after challenge. These findings indicate that inoculation with FIV-pPPR-Deltavif proviral DNA induced resistance to challenge with infectious FIV and that a vif deletion mutant may provide a relatively safe attenuated lentiviral vaccine.

Investigation of recombinant human insulin-like growth factor type I in thymus regeneration in the acute stage of experimental FIV infection in juvenile cats

Thymus involvement and the development of thymic lesions in HIV-1 infection is hypothesized to suppress thymus function and limit T cell maturation and replenishment of the peripheral lymphoid pool. Therapeutic modulation to protect or enhance thymus function may therefore ameliorate peripheral lymphocytopenia and retard disease progression. Thymotrophic agents, such as insulin-like growth factor type I (IGF-I), may therefore represent adjunctive but important methods of treatment to protect or promote thymus function. The assessment of rhIGF-I in lentiviral infection and its impact on the thymus was performed using the feline immunodeficiency virus (FIV) model. Regeneration of the thymus in juvenile cats and amelioration of the thymic lesion after FIV infection was assessed by multiple measurements including thymic weight, stereologic analysis of the thymus cortex and medulla, histologic and immunohistologic analysis, quantitation of thymocyte and peripheral lymphocyte subsets, and quantitative competitive RT-PCR. Evidence of thymic cortical regeneration was observed in FIV-inoculated cats after 12 and 20 weeks of rhIGF-I treatment. Inflammation in the thymus was reduced during this period of treatment in this group of rhIGF-I/FIV-inoculated cats as evidenced by the reduced numbers of B cells detected. Viral replication rates in peripheral lymph nodes were not altered by rhIGF-I treatment and were decreased by 1 log in the thymus after 20 weeks of treatment. Peripheral blood CD4+ T cell counts also increased after 14 weeks of treatment. This suggests that rhIGF-I treatment can enhance thymus function and replenishment of the peripheral T cell pool.

Toward a canine model of atopic dermatitis: amplification of cytokine-gene transcripts in the skin of atopic dogs

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.

Differential cell tropism of feline immunodeficiency virus molecular clones in vivo

Independent studies have demonstrated different cell tropisms for molecular clones of feline immunodeficiency virus (FIV). In this report, we examined three clones, FIV-pF34, FIV-14, and FIV-pPPR, for replication in Crandell feline kidney (CrFK) cells, feline peripheral blood mononuclear cells (PBMC), and feline macrophage cultures. Importantly, cell tropism for these three clones was also examined in vivo. FIV-pF34 replication was efficient in CrFK cells but severely restricted in PBMC, whereas replication of FIV-pPPR was vigorous in PBMC but severely restricted in CrFK cells. FIV-14 replication was productive in both CrFK cells and PBMC. Interestingly, all three molecular clones replicated with similar efficiencies in primary feline monocyte-derived macrophages. In vivo, FIV-pF34 proved least efficient for establishing persistent infection, and proviral DNA when detectable, was localized predominately to nonlymphoid cell populations (macrophages). FIV-pPPR proved most efficient for induction of a persistent viremia in vivo, and proviral DNA was localized predominately in CD4(+) and CD8(+) lymphocyte subsets. FIV-14 inoculation of cats resulted in an infection characterized by seroconversion and localization of proviral DNA in CD4(+) lymphocytes only. Results of this study on diverse FIV molecular clones revealed that in vitro replication efficiency of an FIV isolate in PBMC directly correlated with replication efficiency in vivo, whereas proficiency for replication in macrophages in vitro was not predictive for replication potential in vivo. Also, infection of both CD4(+) and CD8(+) lymphocyte subsets was associated with higher virus load in vivo. Results of the studies on these three FIV clones, which exhibited differential cell tropism, indicated a correlation between in vitro and in vivo cell tropism and virus replication.