Ability of CD8(+) T cell anti-feline immunodeficiency virus activity correlated with peripheral CD4(+) T cell counts and plasma viremia

In the host defense mechanism against feline immunodeficiency virus (FIV) infection, CD8(+) T cells specifically attack virus-infected cells and suppress the replication of the virus in a non-cytolytic manner by secreting soluble factors. In this study, we measured CD8(+) T cell anti-FIV activity in 30 FIV-infected cats. We investigated its relationship with the number of peripheral blood lymphocytes, particularly the CD4(+) T cell and CD8(+) T cell counts, and the relationship between anti-FIV activity and the number of T cells of CD8alpha(+)beta(lo) and CD8alpha(+)beta(-) phenotypes. A clearly significant correlation was observed between anti-FIV activity and the number of CD4(+) T cells. A weaker anti-FIV activity was associated with a greater decrease in the number of CD4(+) T cells. However, there was no significant correlation between anti-FIV activity and the number of B or CD8(+) T cells. Compared with SPF cats, FIV-infected cats had significantly higher CD8alpha(+)beta(lo) T cell and CD8alpha(+)beta(-) T cell counts, but, no significant correlation was observed between these cell counts and anti-FIV activity. This anti-FIV activity significantly correlated with plasma viremia, which was detected in cats with a weak anti-FIV activity. These results suggest that the anti-FIV activity of CD8(+) T cells plays an important role in plasma viremia and the maintenance of CD4(+) T cells in the body. It is unlikely that CD8alpha(+)beta(lo) or CD8alpha(+)beta(-) T cells appearing after FIV infection represent a phenotype of CD8(+) cells with anti-FIV activity.     

Phenotypic changes in CD8+ peripheral blood lymphocytes in cats infected with feline immunodeficiency virus

It is well documented that several cell surface molecules of T lymphocytes are altered by immune activation. We previously reported that feline immunodeficiency virus (FIV) infection induces a reduction in CD8beta chain expression of peripheral blood lymphocytes (PBLs) in cats. In this study, we performed three-color flow-cytometric analysis for activation-associated cell surface molecules (CD2, CD11a, CD45RA-like and major histocompatibility complex antigen class II (MHC II)) and light scatters (cellular size and complexity) to examine whether phenotypic changes also occurred in CD4(+) PBLs in addition to CD8(+) PBLs, of five FIV-infected cats and one uninfected cat. It was shown that (i) CD8alpha(+) PBLs, but not CD4(+) PBLs, had a distinct subpopulation with increased CD11a expression accompanying a reduced CD8beta chain and increased intracellular granules (ii) CD8alpha(+) PBLs, but not CD4(+) PBLs, expressed CD45RA-like antigen with diverse expression levels and (iii) MHC II expression was greater in CD8alpha(+) PBLs than CD4(+) PBLs, and the CD8beta chain reduction was correlated with the MHC II decrease within CD8alpha(+) PBLs. These results suggest that FIV infection induces phenotypically heterogeneous subpopulations in CD8(+) PBLs, including activated phenotypes, rather than in CD4(+) PBLs.     

T-lymphocyte profiles in FIV-infected wild lions and pumas reveal CD4 depletion

Feline immunodeficiency virus (FIV) is a lentivirus related to human immunodeficiency virus (HIV) that causes feline AIDS in the domestic cat (Felis catus). Serological surveys indicate that at least 25 other species of cat possess antibodies that cross-react with domestic cat FIV. Most infected nondomestic cat species are without major symptoms of disease. Long-term studies of FIV genome variation and pathogenesis reveal patterns consistent with coadaptation of virus and host in free-ranging FIV-Ple-infected African lions (Panthera leo) and FIV-Pco-infected pumas (Puma concolor) populations. This report examined correlates of immunodeficiency in wild and captive lions and pumas by quantifying CD5(+), CD4(+), and CD8(+) T-cell subsets. Free-ranging FIV-Ple-infected lions had immunofluorescence flow cytometry (IFC) profiles marked by a dramatic decline in CD4(+) subsets, a reduction of the CD4(+)/CD8(+) ratio, reduction of CD8(+)beta(high) cells, and expansion of the CD8(+)beta(low) subset relative to uninfected lions. An overall significant depletion in CD5(+) T-cells in seropositive lions was linked with a compensatory increase in total CD5(-) lymphocytes. The IFC profiles were altered significantly in 50% of the seropositive individuals examined. The FIV-Pco-infected pumas had a more generalized response of lymphopenia expressed as a significant decline in total lymphocytes, CD5(+) T-cells, and CD5(-) lymphocytes as well as a significant reduction in CD4(+) T-cells. Like lions, seropositive pumas had a significant decline in CD8(+)beta(high) cells but differed by not having compensatory expansion of CD8(+)beta(low) cells relative to controls. Results from FIV-infected lions and pumas parallel human and Asian monkey CD4(+) diminution in HIV and SIV infection, respectively, and suggest there may be unrecognized immunological consequences of FIV infection in these two species of large cats.     

Evolution of replication efficiency following infection with a molecularly cloned feline immunodeficiency virus of low virulence

The development of an effective vaccine against human immunodeficiency virus is considered to be the most practicable means of controlling the advancing global AIDS epidemic. Studies with the domestic cat have demonstrated that vaccinal immunity to infection can be induced against feline immunodeficiency virus (FIV); however, protection is largely restricted to laboratory strains of FIV and does not extend to primary strains of the virus. We compared the pathogenicity of two prototypic vaccine challenge strains of FIV derived from molecular clones; the laboratory strain PET(F14) and the primary strain GL8(414). PET(F14) established a low viral load and had no effect on CD4(+)- or CD8(+)-lymphocyte subsets. In contrast, GL8(414) established a high viral load and induced a significant reduction in the ratio of CD4(+) to CD8(+) lymphocytes by 15 weeks postinfection, suggesting that PET(F14) may be a low-virulence-challenge virus. However, during long-term monitoring of the PET(F14)-infected cats, we observed the emergence of variant viruses in two of three cats. Concomitant with the appearance of the variant viruses, designated 627(W135) and 628(W135,) we observed an expansion of CD8(+)-lymphocyte subpopulations expressing reduced CD8 beta-chain, a phenotype consistent with activation. The variant viruses both carried mutations that reduced the net charge of the V3 loop (K409Q and K409E), giving rise to a reduced ability of the Env proteins to both induce fusion and to establish productive infection in CXCR4-expressing cells. Further, following subsequent challenge of na?ve cats with the mutant viruses, the viruses established higher viral loads and induced more marked alterations in CD8(+)-lymphocyte subpopulations than did the parent F14 strain of virus, suggesting that the E409K mutation in the PET(F14) strain contributes to the attenuation of the virus.     

Feline immunodeficiency virus infection phenotypically and functionally activates immunosuppressive CD4+CD25+ T regulatory cells

Disease progression of feline immunodeficiency virus (FIV) infection is characterized by up-regulation of B7.1 and B7.2 costimulatory molecules and their ligand CTLA4 on CD4(+) and CD8(+) T cells. The CD4(+)CTLA4(+)B7(+) phenotype described in FIV(+) cats is reminiscent of CD4(+)CD25(+)CTLA4(+) cells, a phenotype described for immunosuppressive T regulatory (Treg) cells. In the present study, we describe the phenotypic and functional characteristics of CD4(+)CD25(+) T cells in PBMC and lymph nodes (LN) of FIV(+) and control cats. Similar to Treg cells, feline CD4(+)CD25(+) but not CD4(+)CD25(-) T cells directly isolated from LN of FIV(+) cats do not produce IL-2 and fail to proliferate in response to mitogen stimulation. Unstimulated CD4(+)CD25(+) T cells from FIV(+) cats significantly suppress the proliferative response and the IL-2 production of Con A-stimulated autologous CD4(+)CD25(-) T cells compared with unstimulated CD4(+)CD25(+) T cells from FIV(-) cats. Flow-cytometric analysis confirmed the apparent activation phenotype of the CD4(+)CD25(+) cells in LN of chronically FIV(+) cats, because these cells showed significant up-regulation of expression of costimulatory molecules B7.1, B7.2, and CTLA4. These FIV-activated, anergic, immunosuppressive CD25(+)CTLA4(+)B7(+)CD4(+) Treg-like cells may contribute to the progressive loss of T cell immune function that is characteristic of FIV infection.     

Decline in CD4+ cell numbers in cats with naturally acquired feline immunodeficiency virus infection.

T-cell subsets were studied by fluorescence-activated cell sorter analysis in 57 feline immunodeficiency virus (FIV)-seropositive cats with naturally acquired FIV infection to see whether CD4(+)-CD8+ alterations were comparable to those observed in human immunodeficiency virus-infected patients. CD4+ values were decreased and CD8+ values were increased. The CD4+/CD8+ ratio was reduced to 1.6, compared with 3.3 in 33 FIV-seronegative control cats. Variance analysis of data showed a significant influence of FIV seropositivity, sex, and spaying of female cats on CD4+ values. CD8+ values were significantly influenced by FIV seropositivity, age, and breed. These findings indicate a similarity between FIV and human immunodeficiency virus infections, as far as alterations of T-cell subsets are concerned.     

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.     

Evidence for CD8+ antiviral activity in cats infected with feline immunodeficiency virus.

Human immunodeficiency virus (HIV) causes a long, asymptomatic infection characterized by normal to elevated numbers of circulating CD8+ cells and a progressive decline in CD4+ cells. It has been speculated that HIV-specific antiviral activity driven by CD8+ T cells may control viral replication during this period and maintain the clinically asymptomatic stage of disease. The disease induced in cats by feline immunodeficiency virus (FIV) is similar to HIV in that it is characterized by a long asymptomatic stage with a progressive decline in CD4+ cells, culminating in AIDS. In the present study, we demonstrate that FIV is more readily isolated from CD8+ T-cell-depleted peripheral blood mononuclear cells (PBMC) of FIV-infected cats than from unfractionated PBMC cultures. In addition, CD8+ T cells isolated from FIV-positive cats demonstrating anti-FIV activity in PBMC cultures inhibit FIV infection of FCD4E cells in vitro. Anti-FIV activity is not found in FIV- negative cats and is not characteristic of cats acutely infected with FIV but is present in the majority of chronically infected, clinically asymptomatic and symptomatic cats. Decreases in plasma and cell-associated viremia during the acute-stage FIV infection appears to precede the appearance of CD8+ anti-FIV cells in the circulation. In summary, this study demonstrates a population(s) of CD8+ T cells in chronically FIV-infected cats capable of suppressing FIV replication in cultured PBMC. The significance of anti-FIV CD8+ cells in the immunopathogenesis of the infection and disease progression has yet to be determined.     

Anti-feline immunodeficiency virus (FIV) soluble factor(s) produced from antigen-stimulated feline CD8(+) T lymphocytes suppresses FIV replication

Feline immunodeficiency virus (FIV) causes AIDS-like symptoms in infected cats. Concanavalin A (ConA)-stimulated peripheral blood mononuclear cells (PBMC) from chronically FIV strain PPR-infected cats readily expressed FIV. In contrast, when PBMC from these animals were stimulated with irradiated, autologous antigen-presenting cells (APC), at least a 10-fold drop in viral production was observed. In addition to FIV-specific cytotoxic T lymphocytes, anti-FIV activity was demonstrated in the cell-free supernatants of effector T lymphocytes stimulated with APC. The FIV-suppressive activity was induced from APC-stimulated PBMC of either FIV-infected or uninfected cats but not from ConA-stimulated PBMC. Suppression of FIV strain PPR replication was observed for both autologous and heterologous feline PBMC, was dose dependent, and demonstrated cross-reactivity and cell specificity. It was also demonstrated that the anti-FIV activity originated from CD8(+) T lymphocytes and was mediated by a noncytolytic mechanism.     

Immunologic abnormalities in pathogen-free cats experimentally infected with feline immunodeficiency virus.

Blood mononuclear cells from 47 cats experimentally infected with feline immunodeficiency virus (FIV) were examined by using monoclonal antibodies directed against feline CD4 and CD8 homologs, a pan-T-cell antigen, and cell surface immunoglobulin. Significant inversion of the CD4+/CD8+ T-cell ratio was observed only in cats that were infected for 18 months or more. This inversion was associated with a decrease in the absolute numbers of CD4+ T cells and a concomitant increase in CD8+ cells. However, the total numbers of circulating T and B cells were not significantly reduced. Cats infected with FIV for 24 to 28 months also had significantly elevated levels of serum immunoglobulin G (IgG), but normal levels of IgA and IgM. The long-term decline in CD4+ T cells and hypergammaglobulinemia observed in FIV-infected cats resemble the abnormalities occurring in humans after human immunodeficiency virus infection.     

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.     

The TCR repertoire of an immunodominant CD8+ T lymphocyte population

The TCR repertoire of an epitope-specific CD8(+) T cell population remains poorly characterized. To determine the breadth of the TCR repertoire of a CD8(+) T cell population that recognizes a dominant epitope of the AIDS virus, the CD8(+) T cells recognizing the tetrameric Mamu-A*01/p11C(,CM) complex were isolated from simian immunodeficiency virus (SIV)-infected Mamu-A*01(+) rhesus monkeys. This CD8(+) T cell population exhibited selected usage of TCR V beta families and complementarity-determining region 3 (CDR3) segments. Although the epitope-specific CD8(+) T cell response was clearly polyclonal, a dominance of selected V beta(+) cell subpopulations and clones was seen in the TCR repertoire. Interestingly, some of the selected V beta(+) cell subpopulations and clones maintained their dominance in the TCR repertoire over time after infection with SIV of macaques. Other V beta(+) cell subpopulations declined over time in their relative representation and were replaced by newly evolving clones that became dominant. The present study provides molecular evidence indicating that the TCR repertoire shaped by a single viral epitope is dominated at any point in time by selected V beta(+) cell subpopulations and clones and suggests that dominant V beta(+) cell subpopulations and clones can either be stable or evolve during a chronic infection.     

Serum neutralization of feline immunodeficiency virus is markedly dependent on passage history of the virus and host system.

Sera from feline immunodeficiency virus (FIV)-infected cats exhibited extremely low levels of neutralizing antibodies against virus passaged a few times in vitro (low passage), when residual infectivity was assayed in the CD3+ CD4- CD8- MBM lymphoid cell line or mitogen-activated peripheral blood mononuclear cells. By sharp contrast, elevated titers of highly efficient neutralizing activity against FIV were measured, by use of high-passage virus, in assays on either the fibroblastoid CrFK or MBM cell line. However, high-passage virus behaved the same as low-passage virus after one in vivo passage in a specific-pathogen-free cat and reisolation. Subneutralizing concentrations of infected cat sera enhanced the production of low-passage virus by MBM cells, an effect not seen with high-passage virus in CrFK cells. These qualitative and quantitative discrepancies could not be attributed to differences in the amount of immunoreactive viral material, to the amount of infectious virus present in the viral stocks, or to the presence of anti-cell antibodies. The observed effects were most likely due to the different passage history of the viral preparations used. The observation that neutralizing antibodies detected with high-passage virus were broadly cross-reactive in assays with CrFK cells but isolate specific in MBM cells suggests also that the cell substrate can influence the result of FIV neutralization assays. This possibility could not be tested directly because FIV adapted to grow in CrFK cells had little infectivity for lymphoid cells and vice versa. In vitro exposure to infected cat sera had little or no effect on the ability of in vivo-passaged FIV to infect cats. These data reveal no obvious relationship between titers against high-passage virus and ability to block infectivity of FIV in cats and suggest caution in the use of such assays to measure vaccine efficacy. In conclusion, by contrast with what has been previously reported for the use of CrFK cells and high-passage virus, both natural and experimental infections of cats with FIV generate poor neutralizing antibody responses with regard to in vivo protection.     

Early pathogenesis of transmucosal feline immunodeficiency virus infection

To identify the early target cells and tissues in transmucosal feline immunodeficiency virus (FIV) infection, cats were exposed to a clade C FIV isolate via the oral-nasal or vaginal mucosa and multiple tissues were examined by virus isolation coculture (VI), DNA PCR, catalyzed tyramide signal-amplified in situ hybridization (TSA-ISH), and immunohistochemistry between days 1 and 12 postinoculation (p.i.). FIV RNA was detected in tonsil and oral or vaginal mucosa as early as 1 day p.i. by TSA-ISH and in retropharyngeal, tracheobronchial, or external iliac lymph nodes and sometimes in spleen or blood mononuclear cells by day 2, indicating that regional and distant spread of virus-infected cells occurred rapidly after mucosal exposure. By day 8, viral RNA, DNA, and culturable virus were uniformly detected in regional and distant tissues, connoting systemic infection. TSA-ISH proved more sensitive than DNA PCR in detecting early FIV-infected cells. In mucosal tissues, the earliest demonstrable FIV-bearing cells were either within or subjacent to the mucosal epithelium or were in germinal centers of regional lymph nodes. The FIV(+) cells were of either of two morphological types, large stellate or small round. Those FIV RNA(+) cells which could be colabeled for a phenotype marker, were labeled for either dendritic-cell-associated protein p55 or T-lymphocyte receptor antigen CD3. These studies indicate that FIV crosses mucous membranes within hours after exposure and rapidly traffics via dendritic and T cells to systemic lymphoid tissues, a pathway similar to that thought to occur in the initial phase of infection by the human and simian immunodeficiency viruses.     

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.     

Multivariate Statistical Analyses Demonstrate Unique Host Immune Responses to Single and Dual Lentiviral Infection

Background

Feline immunodeficiency virus (FIV) and human immunodeficiency virus (HIV) are recently identified lentiviruses that cause progressive immune decline and ultimately death in infected cats and humans. It is of great interest to understand how to prevent immune system collapse caused by these lentiviruses. We recently described that disease caused by a virulent FIV strain in cats can be attenuated if animals are first infected with a feline immunodeficiency virus derived from a wild cougar. The detailed temporal tracking of cat immunological parameters in response to two viral infections resulted in high-dimensional datasets containing variables that exhibit strong co-variation. Initial analyses of these complex data using univariate statistical techniques did not account for interactions among immunological response variables and therefore potentially obscured significant effects between infection state and immunological parameters.

Methodology and Principal Findings

Here, we apply a suite of multivariate statistical tools, including Principal Component Analysis, MANOVA and Linear Discriminant Analysis, to temporal immunological data resulting from FIV superinfection in domestic cats. We investigated the co-variation among immunological responses, the differences in immune parameters among four groups of five cats each (uninfected, single and dual infected animals), and the “immune profiles” that discriminate among them over the first four weeks following superinfection. Dual infected cats mount an immune response by 24 days post superinfection that is characterized by elevated levels of CD8 and CD25 cells and increased expression of IL4 and IFNγ, and FAS. This profile discriminates dual infected cats from cats infected with FIV alone, which show high IL-10 and lower numbers of CD8 and CD25 cells.

Conclusions

Multivariate statistical analyses demonstrate both the dynamic nature of the immune response to FIV single and dual infection and the development of a unique immunological profile in dual infected cats, which are protected from immune decline.     

Immunopathologic changes in the thymus during the acute stage of experimentally induced feline immunodeficiency virus infection in juvenile cats.

The feline thymus is a target organ and site of viral replication during the acute stage of feline immunodeficiency virus (FIV) infection. This was demonstrated by histologic, immunohistologic, flow cytometric, and virologic tests. Thymic lesions developed after 28 days postinoculation (p.i.) and included thymitis, premature cortical involution, and medullary B-cell hyperplasia with germinal center formation and epithelial distortion. Alterations in thymocyte subsets also developed. Fewer CD4+ CD8- cells were detected at 28 days p.i., while an increase in CD4- CD8+ cells resulted in an inversion of the thymic CD4/CD8 ratio of single-positive cells, similar to events in peripheral blood. Provirus was present in all thymocyte subpopulations including cortical CD1(hi), CD1(lo), and B cells. The CD1(hi) thymocyte proviral burden increased markedly after 56 days p.i., coincident with the presence of infiltrating inflammatory cells. Increased levels of provirus in the CD1(lo) thymocyte subpopulation were detected prior to 56 days p.i. This was likely due to inclusion of infected infiltrating inflammatory cells which could not be differentiated from mature, medullary thymocytes. Proviral levels in B cells also increased from 70 days p.i. Morphologic alterations, productive viral infection, and altered thymocyte subpopulations suggest that thymic function is compromised, thus contributing to the inability of FIV-infected cats to replenish the peripheral T-cell pool.     

Induction of mucosal homing virus-specific CD8(+) T lymphocytes by attenuated simian immunodeficiency virus

Induction of virus-specific T-cell responses in mucosal as well as systemic compartments of the immune system is likely to be a critical feature of an effective AIDS vaccine. We investigated whether virus-specific CD8(+) lymphocytes induced in rhesus macaques by immunization with attenuated simian immunodeficiency virus (SIV), an approach that is highly effective in eliciting protection against mucosal challenge, express the mucosa-homing receptor alpha4beta7 and traffic to the intestinal mucosa. SIV-specific CD8(+) T cells expressing alpha4beta7 were detected in peripheral blood and intestine of macaques infected with attenuated SIV. In contrast, virus-specific T cells in blood of animals immunized cutaneously by a combined DNA-modified vaccinia virus Ankara regimen did not express alpha4beta7. These results demonstrate the selective induction of SIV-specific CD8(+) T lymphocytes expressing alpha4beta7 by a vaccine approach that replicates in mucosal tissue and suggest that induction of virus-specific lymphocytes that are able to home to mucosal sites may be an important characteristic of a successful AIDS vaccine.     

Structural mapping of CD134 residues critical for interaction with feline immunodeficiency virus

CD134 is a primary binding receptor for feline immunodeficiency virus (FIV), and with CXCR4 facilitates infection of CD4(+) T cells. Human CD134 fails to support FIV infection. To delineate the regions important for defining virus specificity of CD134, we exchanged domains between human and feline CD134. The binding site for FIV surface glycoprotein (SU) is located in domain 1, in a region distinct from the natural ligand (CD134L)-binding site. Mutagenesis showed that Asp60 and Asp62 are required for interaction with FIV, and modeling studies localized these two residues to the outer edge of domain 1. Substitutions S60D and N62D, in conjunction with H45S, R59G and V64K, imparted both FIV SU binding and receptor function to human CD134. Finally, we demonstrated that soluble CD134 facilitates infection of CD134(-) CXCR4(+) target cells in a manner analogous to CD4 augmentation of HIV infection.