Cytokine response in multiple lymphoid tissues during the primary phase of feline immunodeficiency virus infection

Combination Antiretroviral Therapy and Immunophenotype of Feline Immunodeficiency Virus

Feline Immunodeficiency Virus (FIV) causes progressive immune dysfunction in cats similar to human immunodeficiency virus (HIV) in humans. Although combination antiretroviral therapy (cART) is effective against HIV, there is no definitive therapy to improve clinical outcomes in cats with FIV. This study therefore evaluated pharmacokinetics and clinical outcomes of cART (2.5 mg/kg Dolutegravir; 20 mg/kg Tenofovir; 40 mg/kg Emtricitabine) in FIV-infected domestic cats. Specific pathogen free cats were experimentally infected with FIV and administered either cART or placebo treatments (n = 6 each) for 18 weeks, while n = 6 naïve uninfected cats served as controls. Blood, saliva, and fine needle aspirates from mandibular lymph nodes were collected to quantify viral and proviral loads via digital droplet PCR and to assess lymphocyte immunophenotypes by flow cytometry. cART improved blood dyscrasias in FIV-infected cats, which normalized by week 16, while placebo cats remained neutropenic, although no significant difference in viremia was observed in the blood or saliva. cART-treated cats exhibited a Th2 immunophenotype with increasing proportions of CD4+CCR4+ cells compared to placebo cats, and cART restored Th17 cells compared to placebo-treated cats. Of the cART drugs, dolutegravir was the most stable and long-lasting. These findings provide a critical insight into novel cART formulations in FIV-infected cats and highlight their role as a potential animal model to evaluate the impact of cART on lentiviral infection and immune dysregulation.

Effects of Regulatory T Cell Depletion on NK Cell Responses against Listeria monocytogenes in Feline Immunodeficiency Virus Infected Cats

Regulatory T cells (Treg) are key players in the maintenance of peripheral tolerance, preventing autoimmune diseases and restraining chronic inflammatory diseases. Evidence suggests Treg cells and NK cells have important roles in feline immunodeficiency virus (FIV) pathogenesis; however, in vivo studies investigating the interplay between these two cell populations are lacking. We previously described innate immune defects in FIV-infected cats characterized by cytokine deficits and impaired natural killer cell (NK) and NK T cell (NKT) functions. In this study, we investigated whether in vivo Treg depletion by treatment with an anti-feline CD25 monoclonal antibody would improve the innate immune response against subcutaneous challenge with Listeria monocytogenes (Lm). Treg depletion resulted in an increased overall number of cells in Lm-draining lymph nodes and increased proliferation of NK and NKT cells in FIV-infected cats. Treg depletion did not normalize expression of perforin or granzyme A by NK and NKT cells, nor did Treg depletion result in improved clearance of Lm. Thus, despite the quantitative improvements in the NK and NKT cell responses to Lm, there was no functional improvement in the early control of Lm. CD1a+ dendritic cell percentages in the lymph nodes of FIV-infected cats were lower than in specific-pathogen-free control cats and failed to upregulate CD80 even when Treg were depleted. Taken together, Treg depletion failed to improve the innate immune response of FIV-infected cats against Lm and this may be due to dendritic cell dysfunction.

Co-infection with feline retrovirus is related to changes in immunological parameters of cats with sporotrichosis

Feline sporotrichosis due to Sporothrix brasiliensis is frequently severe and often correlated to zoonotic transmission. Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV) cause immunodeficiency in cats; no association has been identified with critical cases of sporotrichosis. Moreover, the cytokine profile in Sporothrix-infected cats and a potential impact of retrovirus co-infections on their immunity is unknown. This study assessed immunological parameters in cats with sporotrichosis with and without FIV or FeLV co-infection. FeLV infection was detected by antigen ELISA and by provirus PCR. FIV infection was investigated through ELISA and Western blot. Cytokine transcription (IFN-γ, IL-4, IL-5, IL-6, IL-10, IL-12, TNF-α) was quantified using RT-qPCR and lymphocyte subpopulations (CD4, CD8, CD5 and CD21) were assessed by flow cytometry. Thirty cats with sporotrichosis were recruited to the study, including three FIV-positive and five FeLV-positive (progressive infection) cats. One cat with regressive FeLV infection was excluded from statistics. In comparison to retrovirus-negative cats, FIV-positive cats and FeLV-positive cats had higher IL-10 levels, FeLV-positive cats had lower IL-4 levels and FIV-positive cats had lower IL-12 levels and a lower CD4+/CD8+ ratio. Remarkably, all cats with poor general condition were FeLV (progressive infection) or FIV-positive, but the retrovirus status was not associated with the sporotrichosis treatment length or outcome. The immunological changes and the more severe clinical presentation observed in cats with retrovirus co-infections encourage future prospective studies that address the impact of these changes on prognostic determinants of feline sporotrichosis and the development of new therapy strategies that control disease spread.

Prior Puma Lentivirus Infection Modifies Early Immune Responses and Attenuates Feline Immunodeficiency Virus Infection in Cats

We previously showed that cats that were infected with non-pathogenic Puma lentivirus (PLV) and then infected with pathogenic feline immunodeficiency virus (FIV) (co-infection with the host adapted/pathogenic virus) had delayed FIV proviral and RNA viral loads in blood, with viral set-points that were lower than cats infected solely with FIV. This difference was associated with global CD4⁺ T cell preservation, greater interferon gamma (IFN-γ) mRNA expression, and no cytotoxic T lymphocyte responses in co-infected cats relative to cats with a single FIV infection. In this study, we reinforced previous observations that prior exposure to an apathogenic lentivirus infection can diminish the effects of acute infection with a second, more virulent, viral exposure. In addition, we investigated whether the viral load differences that were observed between PLV/FIV and FIV infected cats were associated with different immunocyte phenotypes and cytokines. We found that the immune landscape at the time of FIV infection influences the infection outcome. The novel findings in this study advance our knowledge about early immune correlates and documents an immune state that is associated with PLV/FIV co-infection that has positive outcomes for lentiviral diseases.

Phenotypic and functional analysis of CD1a+ dendritic cells from cats chronically infected with feline immunodeficiency virus

Numerous studies suggest dendritic cell (DC) dysfunction is central to the dysregulated immune response during HIV infection; however, in vivo studies are lacking. In the present study we used feline immunodeficiency virus (FIV) infection of cats as a model for HIV-1 infection to assess the maturation and function of dendritic cells, in vivo and in vitro. We compared CD1a+ DC migration, surface phenotype, endocytosis, mixed leukocyte reaction (MLR) and regulatory T cell (Treg) phenotype induction by CD1a+ cells isolated from lymph nodes of FIV-infected and control cats. Results showed that resident CD1a+ DC in lymph nodes of chronically FIV-infected cats are phenotypically mature, can stimulate normal primary T cell proliferation, override Treg suppression and do not skew toward Treg induction. In contrast, FIV infection had deleterious effects on antigen presentation and migratory capacity of CD1a+ cells in tissues.

Evaluation of viremia, proviral load and cytokine profile in naturally feline immunodeficiency virus infected cats treated with two different protocols of recombinant feline interferon omega

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FIV-infected cats were treated with two protocols of rFeIFN-ω (sub-cutaneous vs oral).

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The cytokine profile was evaluated in FIV-cats undergoing rFeIFN-ω therapy.

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There was a decrease of IL-6 mRNA expression in cats treated with the oral protocol.

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There was a reduction of IL-6 plasma levels in cats treated subcutaneously.

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Independently of the protocol, rFeIFN seems to reduce pro-inflammatory stimuli.

This study assesses viremia, provirus and blood cytokine profile in naturally FIV-infected cats treated with two distinct protocols of interferon omega (rFeIFN-ω).

Samples from FIV-cats previously submitted to two single-arm studies were used: 7/18 received the licensed/subcutaneous protocol (SC) while 11/18 were treated orally (PO). Viremia, provirus and blood mRNA expression of interleukin (IL)-1, IL-4, IL-6, IL-10, IL-12p40, Interferon-γ and Tumor Necrosis Factor-α were monitored by Real-Time qPCR. Concurrent plasma levels of IL-6, IL-12p40 and IL-4 were assessed by ELISA.

IL-6 plasma levels decreased in the SC group (p = 0.031). IL-6 mRNA expression (p = 0.037) decreased in the PO group, albeit not sufficiently to change concurrent plasma levels. Neither viremia nor other measured cytokines changed with therapy. Proviral load increased in the SC group (p = 0.031), which can be justified by a clinically irrelevant increase of lymphocyte count.

Independently of the protocol, rFeIFN-ω seems to act on innate immunity by reducing pro-inflammatory stimulus.

In vivo assessment of natural killer cell responses during chronic feline immunodeficiency virus infection

Accumulating evidence suggests that natural killer (NK) cells may have an important role in HIV-1 disease pathogenesis; however, in vivo studies are lacking. Feline immunodeficiency virus (FIV) infection of cats provides a valuable model to study NK cell function in vivo. The immune response against Listeria monocytogenes (Lm) is well characterized, allowing its use as an innate immune probe. We have previously shown that locally delivered IL-15 can improve Lm clearance in FIV-infected animals, and this correlated with an increase in NK cell number. In the present study, chronically FIV-infected and SPF-control cats were challenged with Lm by unilateral subcutaneous injection next to the footpad and then treated with 5-bromo-2′-deoxyuridine (BrdU). The Lm draining and contralateral control lymph nodes were evaluated for NK, NKT, CD4⁺ and CD8⁺ T cell number, proliferation, apoptosis, and NK cell function. Listeria monocytogenes burden was also assessed in both control and Lm draining lymph nodes. NK, NKT, CD4⁺ T and CD8⁺ T cells in the Lm-challenged lymph node of FIV-infected cats did not increase in number. In addition, after Lm challenge, NK cells from FIV-infected cats did not increase their proliferation rate, apoptosis was elevated, and perforin expression was not upregulated when compared to SPF-control cats. The failure of the NK cell response against Lm challenge in the draining lymph node of FIV-infected cats correlates with the delayed control and clearance of this opportunistic bacterial pathogen.

Microsphere immunoassay for the detection of cytokines in domestic cat (Felis catus) plasma: elevated IL-12/23 in acute feline immunodeficiency virus infections

We recently described the development and validation of a highly sensitive and specific microsphere immunoassay capable of simultaneously quantifying three domestic cat cytokines in tissue culture supernatant. Here we describe the modification of this assay to measure interferon gamma (IFNγ), interleukin (IL)-10 and IL-12/IL-23 p40 (IL-12/23) in domestic cat plasma, report values obtained from plasma collected after feline immunodeficiency virus (FIV) exposure, and compare plasma concentrations to blood cell mRNA expression. The validated quantitation limits of this assay are 31-1000 pg/ml for IFNγ, 63-2000 pg/ml for IL-10, and 20-625 pg/ml for IL-12/23. Plasma cytokine levels from domestic cats infected with pathogenic and/or apathogenic FIV were determined at 3-4 and 7-8 weeks post-infection. IL-12/23 was elevated (p<0.05) during acute infection with both FIV strains in two similar studies, conducted five years apart in different feline cohorts (n=44 total animals). IL-12/23 concentrations ranged from 377 to 1904 pg/ml in naïve cats and 552 to 3460 pg/ml in infected cats. In contrast, the majority of plasma samples had IFNγ and IL-10 concentrations below the lowest standard tested. The inability to consistently detect levels of IFNγ and IL-10 in plasma, despite the fact that mRNA changes were detected, suggests that these cytokines may be secreted and/or cleared in a more highly regulated manner than IL-12/23, or perhaps exert local effects under tighter peripheral constraints and/or at a lower effective concentration.

Partial regulatory T cell depletion prior to acute feline immunodeficiency virus infection does not alter disease pathogenesis

Feline immunodeficiency virus (FIV) infection in cats follows a disease course similar to HIV-1, including a short acute phase characterized by high viremia, and a prolonged asymptomatic phase characterized by low viremia and generalized immune dysfunction. CD4(+)CD25(hi)FoxP3(+) immunosuppressive regulatory T (Treg) cells have been implicated as a possible cause of immune dysfunction during FIV and HIV-1 infection, as they are capable of modulating virus-specific and inflammatory immune responses. Additionally, the immunosuppressive capacity of feline Treg cells has been shown to be increased during FIV infection. We have previously shown that transient in vivo Treg cell depletion during asymptomatic FIV infection reveals FIV-specific immune responses suppressed by Treg cells. In this study, we sought to determine the immunological influence of Treg cells during acute FIV infection. We asked whether Treg cell depletion prior to infection with the highly pathogenic molecular clone FIV-C36 in cats could alter FIV pathogenesis. We report here that partial Treg cell depletion prior to FIV infection does not significantly change provirus, viremia, or CD4(+) T cell levels in blood and lymphoid tissues during the acute phase of disease. The effects of anti-CD25 mAb treatment are truncated in cats acutely infected with FIV-C36 as compared to chronically infected cats or FIV-naïve cats, as Treg cell levels were heightened in all treatment groups included in the study within two weeks post-FIV infection. Our findings suggest that the influence of Treg cell suppression during FIV pathogenesis is most prominent after Treg cells are activated in the environment of established FIV infection.

Development and validation of a multiplex microsphere-based assay for detection of domestic cat (Felis catus) cytokines

Cytokines are essential signaling molecules that mediate the innate immune response, and therefore their presence can be of diagnostic, prognostic, and pathogenic significance. Microsphere-based immunoassays allow rapid and accurate evaluation of cytokine levels in several species, including humans, dogs, and mice; however, technology to evaluate domestic cat (Felis catus) cytokines has been limited to single-analyte enzyme-linked immunosorbent assays (ELISAs). Microsphere-based immunoassays provide an attractive alternative technology for detecting and quantifying multiple analytes in a single assay using as little as 50 μl of sample. We describe the development and validation of a microsphere-based assay for three commonly analyzed domestic cat cytokines (gamma interferon, interleukin-10, and interleukin-12/interleukin-23 p40) using reagents from commercially available ELISAs. The assay was optimized for capture and detection antibody concentrations, streptavidin-phycoerythrin concentration, and number of microspheres. The validated lower and upper quantitation limits were 31 and 1,000 pg/ml for gamma interferon, 63 and 2,000 pg/ml for interleukin-10, and 39 and 625 pg/ml for interleukin-12/interleukin-23 p40. Cytokine concentrations in peripheral blood mononuclear cell supernatants were measured, and results obtained by the microsphere assay were correlated with values obtained with commercially available ELISA kits. This technology is a convenient and reproducible assay to evaluate domestic cat cytokine responses elicited by a variety of diseases.

Cytokine dysregulation in early- and late-term placentas from feline immunodeficiency virus (FIV)-infected cats

PROBLEM

Experimental infection of cats with FIV-B-2542 produces high rates of fetal infection and reproductive failure. We hypothesized that dysregulation of placental cytokine expression occurs in FIV-infected queens, and aberrant expression potentiates inflammation and impacts pregnancy outcome. Our purpose was to quantify expression of representative pro-inflammatory cytokines (IL-6, IL-12p35, and IL-1β), IL-10 (anti-inflammatory), and the chemokine SDF-1α in early- and late-term placental tissues.

METHOD OF STUDY

 Real-time reverse transcriptase PCR was used to measure gene expression in placental tissues.

RESULTS

 Increased expression of IL-6 and IL-12p35 and decreased expression of IL-10 occurred in FIV-infected tissues at early pregnancy; at late gestation, IL-6 expression increased and IL-1β and SDF-1α decreased. At late pregnancy, IL-6 expression positively correlated with FIV load. IL-12:IL-10 ratios were higher in infected tissues at early, but not late pregnancy. Fetal non-viability accompanied decreased IL-12p35 and SDF-1α expression at both stages and decreased IL-12:IL-10 ratio at late pregnancy.

CONCLUSION

FIV infection caused a pro-inflammatory placental microenvironment at early, but not late pregnancy.

In vivo depletion of CD4(+)CD25(hi) regulatory T cells is associated with improved antiviral responses in cats chronically infected with feline immunodeficiency virus

Regulatory T (Treg) cells are activated and suppress immune responses during infection, and are characterized as CD4(+)CD25(hi)FOXP3(+). Ex vivo studies demonstrate that Treg cells potentially suppress anti-HIV-1 T cell responses. Lentivirus-induced CD4(+)CD25(hi) Treg cells were first described in feline immunodeficiency virus (FIV)-infected cats. In the present study we demonstrate that anti-feline CD25 monoclonal antibody (mAb) therapy depletes Treg cells in FIV-infected cats for 4 weeks and does not exacerbate viral replication or proinflammatory cytokine production. Significant FIV-specific immune responses are revealed in Treg cell-depleted cats. These anti-FIV effector cells exist prior to Treg cell depletion and are not expanded while Treg cells are depleted. Importantly, cats receiving the Treg cell-depleting mAb are able to produce a robust humoral response to new antigen. We propose that short-term in vivo Treg cell depletion during chronic HIV-1 infection could provide a window of opportunity for therapeutic vaccination in individuals with controlled viral replication.

EIAV S2 enhances pro-inflammatory cytokine and chemokine response in infected macrophages

Equine infectious anemia virus (EIAV) infection is distinctive in that it causes a rapid onset of clinical disease relative to other retroviruses. In order to understand the interaction dynamics between EIAV and the host immune response, we explored the effects of EIAV and its S2 protein in the regulation of the cytokine and chemokine response in macrophages. EIAV infection markedly altered the expression pattern of a variety of pro-inflammatory cytokines and chemokines monitored in the study. Comparative studies in the cytokine response between EIAV(17) and EIAV(17DeltaS2) infection revealed that S2 enhances the expression of IL-1alpha, IL-1beta, IL-8, MCP-2, MIP-1beta and IP-10. Moreover, S2 specifically induced the expression of the newly discovered cytokine, IL-34. Taken together, these results may help explain the effect of cytokine and chemokine dysregulation in EIAV pathogenesis and suggest a role of S2 in optimizing the host cell environment to promote viral dissemination and replication.

Lentivirus-induced immune dysregulation

FIV/HIV infections are associated with an early robust humoral and cellular anti-viral immune response followed by a progressive immune suppression that eventually results in AIDS. Several mechanisms responsible for this immune dysfunction have been proposed including cytokine dysregulation, immunologic anergy and apoptosis, and inappropriate activation of immune regulatory cells. Studies on FIV infection provide evidence for all three. Cytokine alterations include decreases in IL2 and IL12 production and increases in IFNgamma and IL10 in FIV(+) cats compared to normal cats. The elevated IL10:IL12 ratio is associated with the inability of FIV(+) cats to mount a successful immune response to secondary pathogens. Additionally, chronic antigenic (FIV) stimulation results in an increase in the percent of activated T cells expressing B7 and CTLA4 co-stimulatory molecules in infected cats. The expression of these molecules is associated with T cells that are undergoing apoptosis in the lymph nodes. As ligation of CTLA4 by B7 transduces a signal for induction of anergy, one can speculate that the activated T cells are capable of T cell-T cell interactions resulting in anergy and apoptosis. The inability of CD4(+) cells from FIV(+) cats to produce IL2 in response to recall antigens and the gradual loss of CD4(+) cell numbers could be due to B7-CTLA4 interactions. The chronic antigenemia may also lead to activation of CD4(+)CD25(+) T regulatory cells. Treg cells from FIV(+) cats are chronically activated and inhibit the mitogen-induced proliferative response of CD4(+)CD25(-) by down-regulating IL2 production. Although Treg cell activation can be antigen-specific, the suppressor function is not, and thus activated Treg cells would suppress responses to secondary pathogens as well as to FIV. Concomitant with the well-known virus-induced immune suppression is a progressive immune hyper-activation. Evidence for immune hyper-activation includes polyclonal B cell responses, gradual replacement of naïve CD4(+) and CD8(+) T cell phenotypes with activation phenotypes (CD62L(-), B7(+), CTLA4(+)), and the chronic activation of CD4(+)CD25(+) Treg cells. Thus lentivirus infections lead to severe immune dysregulation manifested as both chronic immune suppression and chronic immune activation. FIV infection of cats provides a number of advantages over other lentivirus infections as a model to study this immune dysregulation. It is a natural infection that has existed in balance with the cat's immune system for thousands of years. As such, the natural history and pathogenesis provides an excellent model to study the long-term relationships between AIDS lentivirus and host immune system function/dysregulation.

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.

Mucosal challenge with cell-associated or cell-free feline immunodeficiency virus induces rapid and distinctly different patterns of phenotypic change in the mucosal and systemic immune systems

The majority of human immunodeficiency virus type 1 (HIV-1) infections occur via mucosal transmission through contact with genital secretions containing cell-associated and cell-free virus. However, few studies have assessed whether exposure to cells, HIV-1 infected or uninfected, plays a role in the sexual transmission of HIV-1. This study examined phenotypic changes in mucosal and systemic lymphoid tissue 24 hr after vaginal exposure to in vitro equilibrated infectious doses of cell-associated or cell-free feline immunodeficiency virus, uninfected heterologous cells, or medium alone. We found that even at this early time-point, mucosal exposure to virus induced substantial alterations in the phenotype and distribution of leucocytes, particularly in the tissues of the mucosal immune system. Second, we found that the type of virus inoculum directly influenced the phenotypic changes seen. Vaginal exposure to cell-free virus tended to induce more generalized phenotypic changes, typically in the peripheral immune system (blood and systemic lymph nodes). In contrast, exposure to cell-associated virus was primarily associated with phenotypic shifts in the mucosal immune system (gut and mucosal/draining lymph nodes). In addition, we found that exposure to uninfected heterologous cells also induced alterations in the mucosal immune system. These data suggest that significant immune changes occur within the first 24 hr of virus exposure, well before substantial replication would be anticipated. As the mucosal immune system, and particularly the gut, is an early and persistent target for lentiviral replication, these findings have substantial implications for HIV-1 pathogenesis and vaccine development.

FIV as a Model for HIV: An Overview

Animal models for human immunodeficiency virus (HIV) infection play a key role in understanding the pathogenesis of AIDS and the development of therapeutic agents and vaccines. As the only lentivirus that causes an immunodeficiency resembling that of HIV infection, in its natural host, feline immunodeficiency virus (FIV) has been a unique and powerful model for AIDS research. FIV was first described in 1987 by Niels Pedersen and co-workers as the causative agent for a fatal immunodeficiency syndrome observed in cats housed in a cattery in Petaluma, California. Since this landmark observation, multiple studies have shown that natural and experimental infection of cats with biological isolates of FIV produces an AIDS syndrome very similar in pathogenesis to that observed for human AIDS. FIV infection induces an acute viremia associated with Tcell alterations including depressed CD4 :CD8 T-cell ratios and CD4 T-cell depletion, peripheral lymphadenopathy, and neutropenia. In later stages of FIV infection, the host suffers from chronic persistent infections that are typically self-limiting in an immunocompetent host, as well as opportunistic infections, chronic diarrhea and wasting, blood dyscracias, significant CD4 T-cell depletion, neurologic disorders, and B-cell lymphomas. Importantly, chronic FIV infection induces a progressive lymphoid and CD4 T-cell depletion in the infected cat. The primary mode of natural FIV transmission appears to be blood-borne facilitated by fighting and biting. However, experimental infection through transmucosal routes (rectal and vaginal mucosa and perinatal) have been well documented for specific FIV isolates. Accordingly, FIV disease pathogenesis exhibits striking similarities to that described for HIV-1 infection.

Going wild: lessons from naturally occurring T-lymphotropic lentiviruses

Over 40 nonhuman primate (NHP) species harbor species-specific simian immunodeficiency viruses (SIVs). Similarly, more than 20 species of nondomestic felids and African hyenids demonstrate seroreactivity against feline immunodeficiency virus (FIV) antigens. While it has been challenging to study the biological implications of nonfatal infections in natural populations, epidemiologic and clinical studies performed thus far have only rarely detected increased morbidity or impaired fecundity/survival of naturally infected SIV- or FIV-seropositive versus -seronegative animals. Cross-species transmissions of these agents are rare in nature but have been used to develop experimental systems to evaluate mechanisms of pathogenicity and to develop animal models of HIV/AIDS. Given that felids and primates are substantially evolutionarily removed yet demonstrate the same pattern of apparently nonpathogenic lentiviral infections, comparison of the biological behaviors of these viruses can yield important implications for host-lentiviral adaptation which are relevant to human HIV/AIDS infection. This review therefore evaluates similarities in epidemiology, lentiviral genotyping, pathogenicity, host immune responses, and cross-species transmission of FIVs and factors associated with the establishment of lentiviral infections in new species. This comparison of consistent patterns in lentivirus biology will expose new directions for scientific inquiry for understanding the basis for virulence versus avirulence.

Induction of serum and mucosal FIV-specific immune responses by intranasal immunization with p24Gag

We examined the ability of FIV p24Gag to induce systemic and mucosal FIV-specific immune responses when delivered as a nasal immunogen alone, or with a mucosal adjuvant, Escherichia coli heat labile toxin LT(R192G). Nasal immunization with p24Gag alone induced FIV-specific immune responses but overall responses were weak, transient, and/or present only in a few animals. Co-administration of LT(R192G) resulted in strong FIV-specific serum IgG and enhanced salivary IgA responses. Moreover, FIV-specific IgA was detected in vaginal wash fluid from 6/6 cats co-immunized with LT(R192G) and p24Gag versus 1/6 immunized with p24Gag alone. This is the first report detailing induction of systemic or mucosal FIV-specific immune responses by nasal immunization alone. As such, this study demonstrates that nasal immunization of cats can be a relevant and effective route for the delivery of candidate vaccines. However, while nasal immunization of cats with p24Gag induces antigen-specific systemic immune responses, development of strong systemic and mucosal immune responses requires co-administration of a mucosal adjuvant, such as LT(R192G).

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.

Gene-expression changes induced by Feline immunodeficiency virus infection differ in epithelial cells and lymphocytes

Infection of cats with Feline immunodeficiency virus (FIV) is an important model for understanding comparative lentivirus biology. In vivo, FIV infects lymphocytes and monocyte/macrophages, but in vitro infection is commonly investigated in epithelial Crandell-Reese Feline Kidney (CRFK) cells. In this study, the transcriptional responses of CRFK cells and primary lymphocytes to infection with FIV 34TF, a cloned subtype A virus, and FIV USgaB01, a biological subtype B isolate, were determined. Reverse-transcribed mRNA from both cell types was hybridized to microarrays containing 1700 human expressed sequence tags in duplicate and data were analysed with Significance Analysis of Microarrays (sam) software. Results from six experiments assessing homeostatic cross-species hybridization excluded 3.48 % inconsistently detected transcripts. Analysis of data from five time points over 48 h after infection identified 132 and 24 differentially expressed genes in epithelial cells and lymphocytes, respectively. Genes involved in protein synthesis, the cell cycle, structure and metabolism were affected. The magnitude of gene-expression changes ranged from 0.62 to 1.62 and early gene induction was followed by downregulation after 4 h. Transcriptional changes in CRFK cells were distinct from those in lymphocytes, except for heat-shock cognate protein 71, which was induced at multiple time points in both cell types. These findings indicate that FIV infection induces transcriptional changes of a modest magnitude in a wide range of genes, which is probably reflective of the relatively non-cytopathic nature of virus infection.

The Feline Immunodeficiency Virus-Infected Cat: A Model for Lentivirus-induced Placental Immunopathology and Reproductive Failure (Mini-Review)

PROBLEM

Pediatric human immunodeficiency virus (HIV) infection is largely a result of transplacental transmission, and pregnancy perturbation is more frequent in HIV-infected women. Dysregulation of placental immunology may occur during HIV infection, possibly facilitating HIV vertical transfer and miscarriage. The (FIV)-infected cat is a useful small-animal model for HIV pathogenesis because the viruses share common biological and clinical features. Transplacental transmission is readily achieved experimentally, resulting in a high proportion of infected offspring and frequent reproductive failure.

METHOD OF STUDY

We are using this model to examine lentivirus-induced placental immunopathology to determine the role aberrant immunology plays in intrauterine transmission and pregnancy perturbation.

RESULTS

Kittens were cesarean delivered from FIV-B-2542-infected and control queens at week 8 gestation (1 week short of term), and placental and fetal specimens were collected. On average, control queens delivered 3.8 kittens/litter, and 1 of 31 kittens (3.2%) was non-viable. FIV-infected queens produced 2.7 kittens/litter with 15 of 25 fetuses (60%) non-viable. The virus was detected in 14 of 15 placentas (93%) and 21 of 22 fetuses (95%) using polymerase chain reaction (PCR). Using a one-step, real time reverse transcriptase (RT)-PCR, we measured expression of representative placental T helper 1 (Th1) cytokines, interleukin (IL)-1beta and interferon (IFN)-gamma, a Th2 cytokine, IL-10, and chemokine receptor CXCR4. A comparison of placental cytokine expression between infected and control queens did not reveal differences between the two groups. However, elevated expression of Th1 cytokines and increased Th1/Th2 ratios (IL-1beta/IL-10) occurred in placentas from resorptions, indicating that increased placental Th1 cytokine expression was associated with pregnancy failure in the FIV-infected cat.

CONCLUSION

The potential to establish efficient FIV in utero transmission, coupled with the parallels in immunopathology between FIV-infected cats and HIV-infected humans, suggests the usefulness of the FIV-infected cat as a cost-effective, small-animal model to study lentivirus-induced immunopathology, transplacental infection, and reproductive failure.

Development and validation of puma (Felis concolor) cytokine and lentivirus real-time PCR detection systems

Studies of immune correlates of disease outcome associate humoral immune response mediated by T-helper 2 cytokines (IL-4, IL-10) with more virulent disease relative to a cell-mediated response driven by T-helper 1 cytokines (IL-2, IFN-gamma), particularly in viral and other intra-cellular infections. Specifically, the kinetics of both human immunodeficiency virus (HIV) and feline immunodeficiency virus (FIV) infection are closely associated with Type 1 versus Type 2 cytokine profiles. Puma (Felis concolor) lentivirus (PLV) is closely related to FIV, but based on phylogenetic and clinical studies, is more ancient and less pathogenic. The aims of this study were to validate feline real-time PCR primer/probe systems for puma cytokines and PLV as sensitive, quantitative assays for use in investigations of PLV pathogenicity. We demonstrate that primer/probe systems for IL-4, IL-10, IFN-gamma, TNF-alpha, GAPDH, and the pol region of PLV-1695 amplify puma cytokines and PLV-1695 with high amplification efficiency and sensitivity. Detection of PLV-1695 provirus in experimentally inoculated domestic cats proved to be of equivalent sensitivity, specificity, and positive and negative predictive value to co-culture of one million peripheral blood mononuclear cells (PBMC). Evaluation of cytokine induction during naturally occurring PLV infection will allow insight into mechanisms of host control associated with apathogenic infection. In addition, determination of viral loads during different stages of PLV infection or in different tissues from domestic cats or pumas will further elucidate capacity of these viruses to replicate and establish infection.

Puma lentivirus is controlled in domestic cats after mucosal exposure in the absence of conventional indicators of immunity

A high percentage of free-ranging pumas (Felis concolor) are infected with feline lentiviruses (puma lentivirus, feline immunodeficiency virus Pco [FIV-Pco], referred to here as PLV) without evidence of disease. PLV establishes productive infection in domestic cats following parenteral exposure but, in contrast to domestic cat FIV, it does not cause T-cell dysregulation. Here we report that cats exposed to PLV oro-nasally became infected yet rapidly cleared peripheral blood mononuclear cell (PBMC) proviral load in the absence of a correlative specific immune response. Two groups of four specific-pathogen-free cats were exposed to PLV via the mucosal (oro-nasal) or parenteral (i.v.) route. All animals were PBMC culture positive and PCR positive within 3 weeks postinfection and seroconverted without exhibiting clinical disease; however, three or four oro-nasally infected animals cleared circulating proviral DNA within 3 months. Antibody titers reached higher levels in animals that remained persistently infected. PLV antigen-induced proliferation was slightly greater in mucosally inoculated animals, but no differences were noted in cytotoxic T-lymphocyte responses or cytokine profiles between groups. The distribution of virus was predominantly gastrointestinal as opposed to lymphoid in all animals in which virus was detected at necropsy. Possible mechanisms for viral clearance include differences in viral fitness required for crossing mucosal surfaces, a threshold dose requirement for persistence, or an undetected sterilizing host immune response. This is the first report of control of a productive feline or primate lentivirus infection in postnatally exposed, seropositive animals. Mechanisms underlying this observation will provide clues to containment of immunodeficiency disease and could prompt reexamination of vaccine-induced immunity against human immunodeficiency virus and other lentiviruses.

Placental immunopathology and pregnancy failure in the FIV-infected cat

Placental HIV infections frequently result in infected babies or miscarriage. Aberrant placental cytokine expression during HIV infections may facilitate transplacental viral transmission or pregnancy perturbation. The feline immunodeficiency virus (FIV)-infected cat is a model for HIV infections due to similarities in biology and clinical disease. The purpose of this study was to evaluate placental immunomodulator expression and reproductive outcome using the FIV-infected cat model. Kittens were cesarean delivered from FIV-B-2542-infected and control queens near term; placental and fetal tissues were collected. Real-time RT-PCR was used to measure expression of representative placental Th1 cytokines, interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma), a Th2 cytokine, IL-10, and chemokine receptor CXCR4. On average, control queens delivered 3.8 kittens/litter; 1 of 31 kittens (3.2%) was non-viable. FIV-infected queens produced 2.7 kittens/litter; 15 of 25 concepti (60%) were non-viable. FIV was detected in 14 of 15 placentas (93%) and 21 of 22 fetuses (95%) using PCR. Placental immunomodulator expression did not differ significantly when placentas from infected cats were compared to those of control cats. However, elevated expression of Th1 cytokines and increased Th1/Th2 ratios (IL-1beta/IL-10) occurred in placentas from resorptions. Therefore, increased placental Th1 cytokine expression was associated with pregnancy failure in the FIV-infected cat.

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.

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.

Reduced constitutive cytokine transcription in isolated monocytes of clinically healthy cats, infected with an FIV strain of low pathogenicity

Twenty-five barrier-maintained cats had been experimentally infected for 9.5 months with an FIV strain of low pathogenicity, FIV Zurich 2. Animals were clinically healthy and did not exhibit any haematological changes. FIV proviral DNA was demonstrated in peripheral blood lymphocytes of all cats and in monocytes of most animals, identifying FIV Zurich 2 as a both lympho- and monocytotropic strain. Monocytes were isolated from FIV-infected cats as well as from age-matched uninfected control cats, short-term cultured and examined for cytokine (IL-1beta, IL-6, IL-10, IL-12 p40 and TNF-alpha) transcription by real-time PCR. Constitutive transcription of cytokines in monocytes from FIV-infected cats was restricted to IL-1beta and, in the majority of samples, TNF-alpha. For all cytokines, transcription levels were significantly lower in FIV-infected cats than in control cats. Transcription was often least intense in those samples where FIV infection of the monocyte fraction was not demonstrated. Results show that infection of cats with an FIV strain of low pathogenicity was associated with depression of constitutive cytokine transcription in monocytes even if clinical and haematological changes were not observed.

Failure of FIV-infected cats to control Toxoplasma gondii correlates with reduced IL2, IL6, and IL12 and elevated IL10 expression by lymph node T cells

Increased susceptibility to intracellular pathogens in HIV-infected individuals and FIV-infected cats is attributed to a defective T-helper 1 (Th1) immune response. However, little is known about specific cytokine responses to secondary pathogens. To address this question, control and FIV-infected cats were challenged with Toxoplasma gondii, and lymph node cells analyzed for cytokine mRNA expression. Twenty-four weeks post-FIV infection, prior to T. gondii challenge, IL2 and IL12 mRNAs were depressed, whereas IL10 and IFNgamma mRNAs were increased in CD4+ and CD8+ subsets. Following T. gondii challenge, control cats showed increased expression of IL2, IFNgamma, IL10, IL12, and IL6 mRNAs. In contrast, IL2, IL6, IFNgamma, and IL12 mRNAs were suppressed in FIV-T. gondii co-infected cats, whereas IL10 remained at the high prechallenge levels. IFNgamma and IL10 mRNAs were produced by both CD4+ and CD8+ cells in FIV-T. gondii cats. Elevated IL10 may suppress a Th1 cytokine response to T. gondii challenge.

The regulation of alpha chemokines during HIV-1 infection and leukocyte activation: relevance for HIV-1-associated dementia

Cellular immunity against human immunodeficiency virus type 1 (HIV-1)-infected brain macrophages serves to prevent productive viral replication in the nervous system. Inevitably, during advanced disease, this antiretroviral response breaks down. This could occur through virus-induced dysregulation of lymphocyte trafficking. Thus, we studied the production of non-ELR-containing alpha-chemokines and their receptor (CXCR3) expression in relevant virus target cells. Macrophages, lymphocytes, and astrocytes secreted alpha-chemokines after HIV-1 infection and/or immune activation. Lymphocyte CXCR3-mediated chemotactic responses were operative. In all, alpha-chemokine-mediated T cell migration continued after HIV-1 infection and the neuroinflammatory events operative during productive viral replication in brain.

Long-term changes in adipose tissue in human disease

Redistribution of white adipose tissue is a long-term symptom of several chronic diseases. Although the roles of adipocytes in acute illness have been thoroughly studied, how or why short-term responses of adipose tissue to disease sometimes produce long-term redistribution, and the causal relationship between the anatomical changes and the associated metabolic syndromes are poorly understood. The present paper reviews explanations for the redistribution of adipose tissue after infection with HIV, and in Crohn's disease; both conditions that share the peculiarity of selective expansion of certain adipose depots while others are depleted. HIV adipose tissue redistribution syndrome (HARS) develops gradually after several months of infection with the HIV both in untreated patients and in those taking protease inhibitors and nucleoside reverse transcriptase inhibitors. Some current theories about the causes of HARS are critically assessed, and reasons presented for implicating local interactions between the immune system and perinodal adipocytes. Some evolutionary aspects of conspicuous long-term changes in the distribution of human adipose tissue are discussed. Adipose tissue acts as a social signal, indicating dietary history and previous exposure to pathogens. A distinctive symptom of Crohn's disease is selective enlargement of the mesenteric adipose tissue near the diseased lymph nodes and intestine. Perinodal adipocytes have site-specific properties not found in adipocytes from nodeless depots, such as perirenal and epididymal, that may equip them to interact locally with lymph-node lymphoid cells, making polyunsaturated fatty acids selectively and rapidly available to activated immune cells. Studies of the time course of activation of perinodal adipocytes via the lymph nodes they enclose indicate that prolonged or frequent stimulation recruits more adipocytes to control by immune cells, which may lead to selective enlargement of node-containing depots. These concepts suggest hypotheses about HARS and the anomalous development of mesenteric adipose tissue in Crohn's disease that could form the basis for further investigations.

Constitutive expression of types 1 and 2 cytokines by alveolar macrophages from feline immunodeficiency virus-infected cats

Evidence suggests that feline immunodeficiency virus (FIV), causes pulmonary immunodeficiency. The overall objective of this study was to explore FIV-induced alterations in cell counts and cytokine gene expression in the pulmonary compartment during the acute stage infection. Bronchoalveolar lavage (BAL) cells were collected from FIV-infected and control cats at 0, 4, 10, and 16 weeks post-FIV infection for phenotype and cytokine analysis. The major change in BAL cellular populations following FIV-infection was the development of a neutrophilia. Total BAL cell counts and relative numbers of alveolar macrophages (AM), eosinophils, and lymphocytes remained similar in both groups. The RT-qcPCR analyses of AM purified from BAL showed constitutive expression of TNFα, IL6 and IL10 mRNAs that peaked during the acute stage of infection then declined. The TNFα and IL6 bioactive protein secretion showed a similar response. In contrast, IFNγ expression increased progressively with time after infection and paralleled a progressive increase in FIV-gag mRNA in AM. The IL12 p40 expression also differed from the other cytokines in that there was a progressive decrease in the number of cats with AM IL12 expression following FIV infection. Infection of AM in vitro with FIV also caused an increase in TNFα and IL6 mRNA and bioactive protein suggesting that the increased cytokine response by AM following infection of cats with FIV is an intrinsic characteristic of FIV-infected AM. In summary, pulmonary immune changes seen in FIV-infected cats are similar to those seen in HIV-infected human patients.

Thymic lesions in cats infected with a pathogenic molecular clone or an ORF-A/2-deficient molecular clone of feline immunodeficiency virus

Previous studies using feline immunodeficiency virus (FIV) molecular clones lacking the putative transactivator gene (ORF-A/2) failed to address the issue of thymus pathogenesis or investigate the levels of viral replication in separate lymphoid compartments (Y. Inoshima, et al., J. Virol. 70:8518-8526, 1996; E. E. Sparger, et al., Virology 205:546-553, 1994). Using a highly pathogenic molecular clone of FIV, JSY3, and an ORF-A/2-deficient mutant, JSY3DeltaORF-A/2, we compared viral replication and the extent of thymic dysfunction as measured by the formation of lymphoid follicles and alteration of the thymocyte subsets. Viral replication was reduced in JSY3DeltaORF-A/2-infected cats as measured by lymphocyte coculture, immunohistochemistry, and quantitative PCR. Cell-associated viral load measured by lymphocyte coculture varied in a tissue-dependent manner with replication highest in lymphocytes isolated from the thymus, lower in those from the peripheral blood, and lowest in those from lymph node. Thymic proviral load and the number of viral p24 Gag-positive cells within the thymus detected by immunohistochemistry were also reduced. In addition, the onset of a reduced peripheral blood CD4/CD8 ratio was delayed in JSY3DeltaORF-A/2-infected cats. The formation and extent of thymic lymphoid follicular hyperplasia were similar in JSY3 and JSY3DeltaORF-A/2-infected cats as measured by anticytokeratin immunohistochemistry and flow cytometry for percent pan T-negative, immunoglobulin G-positive cells within the thymus. In contrast, comparison of thymocyte subpopulations demonstrated a reduced expansion of single-positive CD4(-) CD8(+) thymocytes in JSY3DeltaORF-A/2-infected cats. Level of viral replication, therefore, may not correlate with the formation of thymic lymphoid follicles but may correlate with the expansion of the single-positive CD4(-) CD8(+) thymocyte subpopulation.

CD8+ thymic lymphocytes express reduced levels of CD8beta and increased interferon gamma in cats perinatally infected with the JSY3 molecular clone of feline immunodeficiency virus

Biological isolates of feline immunodeficiency virus (FIV) cause a relative expansion of activated single-positive CD8(+) (SP CD8(+)) lymphocytes within the thymus of infected cats. In this study, thymic SP CD8(+) lymphocytes were analyzed from cats inoculated as neonates with a pathogenic molecular clone of FIV, JSY3, which was previously derived from the wild-type biological isolate FIV(NCSU-1) (NCSU-1). Four cats were inoculated intraperitoneally with NCSU-1 and compared with 11 cats inoculated with JSY3. Five control cats matched in litter and age were administered an intraperitoneal sham inoculum. Between 12 and 16 weeks postinoculation, interferon-gamma (IFN-gamma) mRNA was quantified by RT-PCR in freshly isolated thymocytes and peripheral blood mononuclear cells (PBMCs). The quantity of IFN-gamma mRNA was increased more than 10-fold in thymocytes and PBMCs of 13 of 13 FIV-inoculated cats as compared with the sham-inoculated controls. IFN-gamma mRNA coenriched with magnetically sorted CD8(+) PBMCs and single-positive (SP) CD8(+) thymocytes. Cells expressing IFN-gamma mRNA were located within the thymic perivascular zone, along the corticomedullary junction, and adjacent to lymphoid follicles. The expansion of thymic SP CD8(+) cells was associated with an increase in CD8alpha(+)/beta(neg) and CD8alpha(+)/beta(lo) phenotypes, the latter population resembling a previously reported memory/effector peripheral blood cell with FIV suppressor activity. From these data we conclude that JSY3 and NCSU-1 induce similar phenotypic changes in thymic and peripheral blood CD8(+) cells. Thus, JSY3 is pathogenic for the thymus in vivo and will be useful for defining determinants of the CD8(+) cell response in this pediatric AIDS model.

Antiviral therapy reduces viral burden but does not prevent thymic involution in young cats infected with feline immunodeficiency virus

The thymus is a major target organ in human immunodeficiency virus type 1 (HIV-1)-infected children and feline immunodeficiency virus (FIV)-infected young cats (G. A. Dean and N. C. Pedersen, J. Virol. 72:9436-9440, 1998; J. L. Heeney, Immunol. Today 16:515-520, 1995; S. M. Schnittman et al., Proc. Natl. Acad. Sci. USA 87:7727-7731, 1990; T. A. Seemayer et al., Hum. Pathol. 15:469-474, 1984; H.-J. Shuurn et al., Am. J. Pathol. 134:1329-1338, 1989; J. C. Woo et al., J. Virol. 71:8632-8641, 1997; J. C. Woo et al., AIDS Res. Hum. Retrovir. 15:1377-1388, 1999). It is likely that the accelerated disease process in children and cats is due to infection of the thymus during the time when generation of naive T lymphocytes is needed for development of the mature immune system. Zidovudine (ZDV) monotherapy, which is used to prevent and treat perinatal HIV-1 infection (R. Sperling, Infect. Dis. Obstet. Gynecol. 6:197-203, 1998), previously had been shown to reduce viral burden in FIV-infected young cats (K. A. Hayes et al., J. Acquir. Immune Defic. Syndr. 6:127-134, 1993). The purpose of this study was to evaluate the effect of drug-induced reduction of viral burden in the thymus on virus-mediated thymic involution and peripheral blood CD4 decline using FIV-infected cats as a model for pediatric HIV-1 infection. Eight-week-old cats were randomly assigned to uninfected, saline-treated; uninfected, ZDV-treated; FIV-infected, saline-treated; and FIV-infected, ZDV-treated groups. Parameters measured included blood lymphocyte numbers, viral load in blood and thymic tissue, and thymic histopathology. While the viral burden was significantly reduced by ZDV monotherapy in peripheral blood lymphocytes, plasma, and thymus, thymic lesions were similar for the treated and untreated FIV-infected cats. Further, markedly lowering the viral burden did not increase blood CD4 lymphocyte numbers or prevent their decline. The data suggest that an inflammatory process continued in spite of reduced virus replication. These observations imply that reducing virus load and limiting thymic inflammation are separate factors that must be addressed when considering therapeutic strategies aimed at preserving thymic function.

The effects of feline retroviruses on cytokine expression

To identify potential roles of cytokines in retroviral pathogenesis, we used reverse transcription-quantitative competitive polymerase chain reaction (RT-qcPCR) assays to characterize mRNA levels of 19 different lymphokines, chemokines, monokines and hematopoietic growth factors in three feline cell lines productively infected with subgroup A feline leukemia virus (FeLV-A) or various feline immunodeficiency virus (FIV) strains. Infection of a CD8+, CD5- large granular lymphocyte (LGL) cell line with FeLV-A activated expression of interleukin-7 (IL-7), induced modest (4-fold) increases in granulocyte/macrophage colony-stimulating factor (GM-CSF) and leukemia inhibitory factor (LIF) transcripts, and decreased transforming growth factor-beta (TGF-beta) mRNA (4-fold). The LGL cells were not susceptible to infection by FIV. Infection of MYA-1 cells, a CD4+ T-lymphoblastoid cell line, with FeLV-A activated expression of macrophage inflammatory protein-1alpha (MIP-1alpha), increased transcript levels of GM-CSF (8-fold), macrophage CSF (M-CSF) (16-fold) and stem cell factor (SCF) (250-fold), and decreased (4-fold) expression of IL-10 and tumor necrosis factor-alpha (TNF-alpha). Productive infection with four different FIV molecular clones caused progressive MYA-1 cell death; however, the mRNA expression profiles were unchanged except for 2- to 4-fold increases in M-CSF and 16- to 500-fold increases in SCF. Thus, FIV-induced MYA-1 cytopathicity was not associated with dysregulation of pro-apoptotic or survival factor transcript levels. Lastly, productive infection of PNI cells, a marrow-derived fibroendothelial cell line, with FeLV-A or any of three FIV strains induced 4-fold higher levels of IL-12p40 transcripts and variably higher levels (4- to 64-fold) of GM-CSF. Two viral strains, the FIV-14 molecular clone and the clinical isolate FIV-5122, caused syncytia formation and unique activation of IL-1beta and stromal cell-derived factor-1 (SDF-1) expression, suggesting a potential role for those factors in viral spread and/or cytopathicity. In addition, infection with FIV-5122, but not the other FIV strains or FeLV-A, induced significant increases in mRNA levels of the hematopoietic inhibitors TNF-alpha and MIP-1alpha, along with increased concentrations of soluble proteins in culture supernatants. Consistent with this, supernatant from FIV-5122 infected PNI cells suppressed hematopoietic progenitor growth in colony assays, compared to supportive activities in supernatants from other infected or uninfected PNI cell cultures. Together, these data demonstrate that feline retroviruses alter cytokine mRNA levels in general and strain-specific patterns. These changes may result in specific alterations in cell function and contribute to retroviral pathogenesis. Our observations provide a basis for directed studies of candidate factors within the hematopoietic, thymic and lymphoid microenvironments.