Inhibition of SIV/SMM replication in vitro by CD8+ cells from SIV/SMM infected seropositive clinically asymptomatic sooty mangabeys.

Several investigators have demonstrated the ability of CD8+ T cells from HIV-1 infected humans and SIV infected rhesus macaques to inhibit viral replication in vitro. In this report we show that CD8+ cells from naturally SIV infected sooty mangabeys also have the ability to inhibit viral replication in vitro. In addition, initial experiments which seek to elucidate the mechanism and antigen specificity of CD8-mediated suppression are described.     

Phenotypic and functional differences in NK and LAK cells in the peripheral blood of sooty mangabeys and rhesus macaques

Greater than 75% of the sooty mangabey monkeys at the Yerkes Regional Primate Research Center are naturally infected with SIV without any apparent clinical symptomology. On the other hand, experimental infection of rhesus macaques with SIV results in a clinical syndrome similar to human AIDS. These differences with regard to SIV infection prompted us to examine the natural immunosurveillance system of peripheral blood mononuclear cells (PBMC) from SIV-infected and uninfected monkeys of these two species. Phenotypic and functional studies of precursor and effector NK and LAK cells in the PBMC from these two species were carried out using monoclonal reagents, flow microfluorometry (FMF), and the standard in vitro 51Cr release assay against prototype K562 (NK sensitive) and RAJI (NK resistant, LAK susceptible) target cell lines. Data indicate that both NK and LAK cell activities in the PBMC of sooty mangabeys were significantly (P less than 0.01) greater than those in rhesus macaques. The predominant NK effector cells and LAK cell precursors were shown to be Leu 19-CD8+ in the PBMC of sooty mangabeys and Leu19+ CD8- in the PBMC of rhesus macaques as determined by panning depletion techniques and FMF analysis. On the other hand, the predominant LAK effector cells were found to be dual marked Leu 19+ CD8+ in rhesus macaques and Leu 19- CD8+ in sooty mangabeys. These qualitative and quantitative differences were not due to SIV infection of these two species since PBMC from both SIV-seropositive and virus-positive and SIV-sero-negative and virus-negative monkeys gave similar results. Moreover, of importance is the finding that the functional NK and LAK precursor cells are CD8+ and CD8- in sooty mangabeys and rhesus macaques, respectively. These data may have implications for the natural SIV/SMM virus-positive asymptomatic state of sooty mangabeys and may provide useful tools for tracing the ontogeny and lineage derivation of NK and LAK cells.     

Th-1-type cytotoxic CD8+ T-lymphocyte responses to simian immunodeficiency virus (SIV) are a consistent feature of natural SIV infection in sooty mangabeys

Sooty mangabeys are a natural host of simian immunodeficiency virus (SIV) that remain asymptomatic and do not exhibit increased immune activation or increased T-lymphocyte turnover despite sustained high levels of SIV viremia. In this study we asked whether an altered immune response to SIV contributes to the lack of immunopathology in sooty mangabeys as opposed to species with pathogenic lentivirus infection. SIV-specific cellular immune responses were investigated in a cohort of 25 sooty mangabeys with natural SIV infection. Gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay responses targeting a median of four SIV proteins were detected in all 25 mangabeys and were comparable in magnitude to those of 13 rhesus macaques infected with SIVmac251 for more than 6 months. As with rhesus macaques, Th2 ELISPOT responses to SIV were absent or >10-fold lower than the IFN-gamma ELISPOT response to the same SIV protein. The SIV-specific ELISPOT response was predominantly mediated by CD8+ T lymphocytes; the frequency of circulating SIV-specific CD8+ T lymphocytes ranged between 0.11% and 3.26% in 13 mangabeys. Functionally, the SIV-specific CD8+ T lymphocytes were cytotoxic; secreted IFN-gamma, tumor necrosis factor alpha, and macrophage inflammatory protein 1beta; and had an activated effector phenotype. Although there was a trend toward higher frequencies of SIV-specific CD8+ T lymphocytes in mangabeys with lower viral loads, a significant inverse correlation between SIV viremia and SIV-specific cellular immunity was not detected. The consistent detection of Th1-type SIV-specific cellular immune responses in naturally infected sooty mangabeys suggests that immune attenuation is neither a feature of nor a requirement for maintenance of nonpathogenic SIV infection in its natural host.     

Flow microfluorometric analysis of peripheral blood mononuclear cells from nonhuman primates: Correlation of phenotype with immune function

A panel of monoclonal antibody reagents has been identified that can be used for routine monitoring of subsets of peripheral blood mononuclear cells (PBMC) from Macaca mulatta (rhesus macaques), Macaca nemestrina (pig-tailed macaques), and Cercocebus atys (sooty mangabeys). The procedure uses fluorescein and phycoerythrin conjugates of the monoclonal antibodies in appropriate combinations, so that two-color microfluorometric analyses can be readily performed on as little as 1.2 ml of EDTA blood. PBMC from a total of 20 normal adult rhesus macaques, 21 normal adult pig-tailed macaques, 4 SIV^? sooty mangabeys, and 16 SIV⁺ adult sooty mangabeys were analyzed with the panel of monoclonal reagents and flow microfluorometry. The mean frequency, absolute numbers, and range for each subset in these nonhuman primate species are described. Sooty mangabeys appeared markedly different from the other two primate species. The PBMCs from the mangabeys had a higher mean frequency and absolute number of total T cells, Leu-3a⁺/18^? T cells, suppressor (Leu?2a⁺) T cells, which were HLA-DR⁺, and IL-2R⁺ cells. Functional helper, suppressor, natural killer (NK), lymphokine activated killer (LAK), and antigen-presenting cell studies were also performed to correlate phenotype with immune function. Data indicate that Leu?3a⁺ T cells (CD4⁺) and Leu?2a⁺ T cells (CD8⁺) in these primate species represent human equivalents of helper and suppressor T cells, respectively. NK and LAK effector cells in the rhesus and pig-tailed macaques appear to be predominantly Leu?19⁺. In contrast, Leu?2a⁺ cells appear to be the predominant NK and LAK effector cell in sooty mangabeys. These data provide a basis for routine evaluation of lymphocyte subsets in these nonhuman primate species, and provide a means to correlate phenotype with immune function.     

Inhibition of simian immunodeficiency virus (SIV) replication by CD8 + cells of SIV-infected rhesus macaques: Implications for immunopathogenesis

The ability of the CD8 + cells from simian immunodeficiency virus (SIV)-infected rhesus macaques to inhibit SIV replication was investigated. Inhibition was produced by a heat-stable soluble factor of molecular size greater than 10kDa. CD8 + supernatants from some macaques were found not only to suppress SIV growth but also to be cytolytic toward both infected and uninfected CD4+ cells. Such indiscriminate CD8 + cell-mediated cell killing may therefore account for DC4 + cell depletion in certain SIV-infected macaques.     

Similar Impact of CD8+ T Cell Responses on Early Virus Dynamics during SIV Infections of Rhesus Macaques and Sooty Mangabeys

Despite comparable levels of virus replication, simian immunodeficiency viruses (SIV) infection is non-pathogenic in natural hosts, such as sooty mangabeys (SM), whereas it is pathogenic in non-natural hosts, such as rhesus macaques (RM). Comparative studies of pathogenic and non-pathogenic SIV infection can thus shed light on the role of specific factors in SIV pathogenesis. Here, we determine the impact of target-cell limitation, CD8+ T cells, and Natural Killer (NK) cells on virus replication in the early SIV infection. To this end, we fit previously published data of experimental SIV infections in SMs and RMs with mathematical models incorporating these factors and assess to what extent the inclusion of individual factors determines the quality of the fits. We find that for both rhesus macaques and sooty mangabeys, target-cell limitation alone cannot explain the control of early virus replication, whereas including CD8+ T cells into the models significantly improves the fits. By contrast, including NK cells does only significantly improve the fits in SMs. These findings have important implications for our understanding of SIV pathogenesis as they suggest that the level of early CD8+ T cell responses is not the key difference between pathogenic and non-pathogenic SIV infection.     

中药复方连黄对小鼠T淋巴细胞亚群CD4~+、CD8~+的影响

目的探讨中药复方连黄对小鼠T淋巴细胞亚群CD4+、CD8+的影响.方法 T淋巴细胞亚群测定采用单克降抗体直接免疫荧光技术,通过流式细胞仪测定.结果经统计学分析,与对照组比较,中药复方连黄能不同程度地使CD4+、CD4+/CD8+升高,而使CD8+下降.结果表明,中药复方连黄对细胞免疫功能具有调节作用.     

Diverse Host Responses and Outcomes following Simian Immunodeficiency Virus SIVmac239 Infection in Sooty Mangabeys and Rhesus Macaques

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) do not develop immunodeficiency despite the presence of viral loads of 10⁵ to 10⁷ RNA copies/ml. To investigate the basis of apathogenic SIV infection in sooty mangabeys, three sooty mangabeys and three rhesus macaques were inoculated intravenously with SIVmac239 and evaluated longitudinally for 1 year. SIVmac239 infection of sooty mangabeys resulted in 2- to 4-log-lower viral loads than in macaques and did not reproduce the high viral loads observed in natural SIVsmm infection. During acute SIV infection, polyclonal cytotoxic T-lymphocyte (CTL) activity coincident with decline in peak plasma viremia was observed in both macaques and mangabeys; 8 to 20 weeks later, CTL activity declined in the macaques but was sustained and broadly directed in the mangabeys. Neutralizing antibodies to SIVmac239 were detected in the macaques but not the mangabeys. Differences in expression of CD38 on CD8⁺ T lymphocytes or in the percentage of naive phenotype T cells expressing CD45RA and CD62L-selection did not correlate with development of AIDS in rhesus macaques. In macaques, the proportion of CD4⁺ T lymphocytes expressing CD25 declined during SIV infection, while in mangabeys, CD25-expressing CD4⁺ T lymphocytes increased. Longitudinal evaluation of cytokine secretion by flow cytometric analysis of unstimulated lymphocytes revealed elevation of interleukin-2 and gamma interferon in a macaque and only interleukin-10 in a concurrently infected mangabey during acute SIV infection. Differences in host responses following experimental SIVmac239 infection may be associated with the divergent outcome in sooty mangabeys and rhesus macaques.     

Limited CD4+ T cell proliferation leads to preservation of CD4+ T cell counts in SIV-infected sooty mangabeys

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections result in chronic virus replication and progressive depletion of CD4+ T cells, leading to immunodeficiency and death. In contrast, ‘natural hosts’ of SIV experience persistent infection with high virus replication but no severe CD4+ T cell depletion, and remain AIDS-free. One important difference between pathogenic and non-pathogenic infections is the level of activation and proliferation of CD4+ T cells. We analysed the relationship between CD4+ T cell number and proliferation in HIV, pathogenic SIV in macaques, and non-pathogenic SIV in sooty mangabeys (SMs) and mandrills. We found that CD4+ T cell proliferation was negatively correlated with CD4+ T cell number, suggesting that animals respond to the loss of CD4+ T cells by increasing the proliferation of remaining cells. However, the level of proliferation seen in pathogenic infections (SIV in rhesus macaques and HIV) was much greater than in non-pathogenic infections (SMs and mandrills). We then used a modelling approach to understand how the host proliferative response to CD4+ T cell depletion may impact the outcome of infection. This modelling demonstrates that the rapid proliferation of CD4+ T cells in humans and macaques associated with low CD4+ T cell levels can act to ‘fuel the fire’ of infection by providing more proliferating cells for infection. Natural host species, on the other hand, have limited proliferation of CD4+ T cells at low CD4+ T cell levels, which allows them to restrict the number of proliferating cells susceptible to infection.     

Heterogeneity in phenotype and function of CD8+ and CD4/CD8 double‐negative Natural Killer T cell subsets in sooty mangabeys

Background We have recently reported the presence of CD8⁺ and CD4/8 double‐negative (DN) natural killer T (NKT) lymphocytes in sooty mangabeys. To investigate differences in the two NKT cell subsets, we compared the phenotype and function of sooty mangabey CD8⁺ and DN NKT cells. Methods Flow‐sorted NKT lymphocytes from one SIV‐negative sooty mangabey were subjected to limiting dilution cloning. Invariant NKT clones were characterized by flow cytometry and cytokine ELISA. Results The majority of NKT clones displayed an effector memory phenotype and expressed CXCR3 and NKG2D. While CD8⁺ NKT subsets expressed significantly higher levels of granzyme B and perforin and produced more IFN‐γ, the DN NKT subsets secreted significantly more IL‐4, IL‐13, and IL‐10. Conclusions The Th1 and Th2 cytokine bias of CD8⁺ and DN NKT cells, respectively, indicates the presence of functionally heterogeneous populations of NKT cells in sooty mangabeys.     

Lymphokine-activated killer (LAK) cells. VI. NK1.1+, CD3+ LAK effectors are derived from CD4-, CD8-, NK1.1- precursors.

Normal murine splenocytes cultured with IL2 for 6, but not 3, days contained an NK1.1+, CD3+ lytically active subset. These lymphocytes were not derived from NK1.1+ precursors since NK1.1+ cells, purified by flow cytometry, failed to express CD3, as determined by the 145-2C11 mAb, on their surface even after culture with IL2 for 6 days. Instead, the precursors of the NK1.1+, CD3+ effectors were contained in a B cell-depleted CD4-, CD8-, NK1.1- splenic subset. Freshly obtained CD4-, CD8-, NK1.1- splenocytes were mostly CD3+, CD5+, B220-, had no spontaneous lytic activity against YAC-1, and were unable to mediate anti-CD3 directed lysis against FcR-bearing target cells. Culture of the CD4-, CD8-, NK1.1- splenocytes with IL2, for 6 days, resulted in the development of NK1.1+, CD3+, B220+ effectors 40% of which were CD5dim and 20-25% of which expressed TCR-V beta 8 as determined by the F23.1 mAb. The acquisition of NK1.1, B220, and lytic activity by this triple-negative subset was readily inhibited by cyclosporine A (CSA). On the other hand, CSA had no effect on the acquisition of B220 or lytic activity by NK1.1+ precursors obtained by flow cytometry sorting. Moreover, all of the NK1.1+ cells generated by IL2 culture of splenocytes obtained from mice depleted of NK1.1+ lymphocytes (by in vivo injection of anti-NK1.1 mAb) coexpressed CD3 on their surface and were thus distinct from classical NK cells. These findings demonstrate that splenic NK cells do not express or acquire CD3; that the NK1.1+, CD3+ LAK effectors are derived from an NK1.1- precursor; and that CSA is exquisitely selective in its inhibitory effect on LAK generation.     

Variation in the CD4+ and CD8+ populations in lymph nodes does not reflect that in the blood during SIVMNE/E11S infection of macaques.

The decline in the CD4% and CD4/CD8 ratios have been compared in lymph nodes and blood from SIVMNE/E11S infected rhesus macaques. The results indicate that loss from the LN CD4+ cell pool does not occur until CD4/CD8 ratios of less than 0.5 is reached in blood. These changes also correlate with the ability to isolate virus from the blood and the transition of CD45RAhi to highly activated CD45RAlo CD8+ cells both of which may play a role in eliminating CD4+ cells. In end-stage disease, CD8+ cells also decline in LN and mitogen responsiveness no longer exists in any nodes. Interestingly at this stage, the circulating CD8% increases significantly and represents the only source of functional T cells remaining in the body.     

Importance of the CD3 marker for evaluating changes in rhesus macaque CD4/CD8 T-cell ratios

BACKGROUND: Until recently, there were no CD3 antibodies that crossreacted with rhesus macaque T cells. Consequently, studies relying on CD8 counts or CD4/CD8 ratios enumerated this subpopulation on the basis of CD8+ or CD8bright+ staining. We used a rhesus-specific, anti-CD3 antibody to better define the CD8+ T-cell population, and to show the effects of better measurements on CD4/CD8 ratios and changes in T cells as macaques age. METHODS: We used three-color flow cytometry to measure CD4 and CD8 populations with and without CD3 costaining. Venous blood samples were obtained from 52 colony-bred macaques between 2 months and 9 years of age. RESULTS: The CD8+ T cells defined by CD3 and CD8 double staining were approximately 60% of all cells that were stained by CD8 alone. Improved detection of this lymphocyte subset showed that CD4/CD8 ratios were close to the range of 1.5-2.0. Declining CD4/CD8 ratios during aging are predominantly due to decreasing CD4+ T-cell counts. CONCLUSIONS: Better quantitation of the CD8+ T-cell population showed that the CD4/CD8 ratio was not inverted as had been reported, but is actually very similar to the values observed in human beings. Although the two species differ in the pattern of CD8 expression, the general immune system characteristics are very similar.     

Phenotypic and functional analysis of murine CD3+,CD4-,CD8- TCR-gamma delta-expressing peripheral T cells

Murine CD3+,CD4-,CD8- peripheral T cells, which express various forms of the TCR-gamma delta on their cell surface, have been characterized in terms of their cell-surface phenotype, proliferative and lytic potential, and lymphokine-producing capabilities. Three-color flow cytofluorometric analysis demonstrated that freshly isolated CD3+,CD4-, CD8- TCR-gamma delta lymph node cells were predominantly Thy-1+,CD5dull,IL-2R-,HSA-,B220-, and approximately 70% Ly-6C+ and 70% Pgp-1+. After CD3+,CD4-,CD8-splenocytes were expanded for 7 days in vitro with anti-CD3-epsilon mAb (145-2C11) and IL-2, the majority of the TCR-gamma delta cells expressed B220 and IL-2R, and 10 to 20% were CD8+. In comparison to CD8+ TCR-alpha beta T cells, the population of CD8+ TCR-gamma delta-bearing T cells exhibited reduced levels of CD8, and about 70% of the CD8+ TCR-gamma delta cells did not express Lyt-3 on the cell surface. Functional studies demonstrated that splenic TCR-gamma delta cells proliferated when stimulated with mAb directed against CD3-epsilon, Thy-1, and Ly-6C, but not when incubated with an anti-TCR V beta 8 mAb, consistent with the lack of TCR-alpha beta expression. In addition, activated CD3+,CD4-,CD8- peripheral murine TCR-gamma delta cells were capable of lysing syngeneic FcR-bearing targets in the presence of anti-CD3-epsilon mAb and the NK-sensitive cell line, YAC-1, in the absence of anti-CD3-epsilon mAb. Finally, activated CD3+, CD4-,CD8-,TCR-gamma delta+ splenocytes were also capable of producing IL-2, IL-3, IFN-gamma, and TNF when stimulated in vitro with anti-CD3-epsilon mAb.     

IgG Fc receptor III homologues in nonhuman primate species: genetic characterization and ligand interactions

Ig Fc receptors bind to immune complexes through interactions with the Fc regions of specific Ab subclasses to initiate or inhibit the defense mechanisms of the leukocytes on which they are expressed. The mechanism of action of IgG-based therapeutic molecules, which are routinely evaluated in nonhuman primate models, involves binding to the low-affinity FcRIII (CD16). The premise that IgG/CD16 interactions in nonhuman primates mimic those present in humans has not been evaluated. Therefore, we have identified and characterized CD16 and associated TCR zeta-chain homologues in rhesus macaques, cynomolgus macaques, baboons, and sooty mangabeys. Similar to humans, CD16 expression was detected on a lymphocyte subpopulation, on monocytes, and on neutrophils of sooty mangabeys. However, CD16 was detected only on a lymphocyte subpopulation and on monocytes in macaques and baboons. A nonhuman primate rCD16 generated in HeLa cells interacted with human IgG1 and IgG2. By contrast, human CD16 binds to IgG1 and IgG3. As shown for humans, the mAb 3G8 was able to block IgG binding to nonhuman primate CD16 and inhibition of nonhuman primate CD16 N-glycosylation enhanced IgG binding. Clearly, differences in interaction with IgG subclasses and in cell-type expression should be considered when using these models for in vivo evaluation of therapeutic Abs.     

Loss of IL-17-producing CD8 T cells during late chronic stage of pathogenic simian immunodeficiency virus infection

Progressive disease caused by pathogenic SIV/HIV infections is marked by systemic hyperimmune activation, immune dysregulation, and profound depletion of CD4(+) T cells in lymphoid and gastrointestinal mucosal tissues. IL-17 is important for protective immunity against extracellular bacterial infections at mucosa and for maintenance of mucosal barrier. Although IL-17-secreting CD4 (Th17) and CD8 (Tc17) T cells have been reported, very little is known about the latter subset for any infectious disease. In this study, we characterized the anatomical distribution, phenotype, and functional quality of Tc17 and Th17 cells in healthy (SIV-) and SIV+ rhesus macaques. In healthy macaques, Tc17 and Th17 cells were present in all lymphoid and gastrointestinal tissues studied with predominance in small intestine. About 50% of these cells coexpressed TNF-α and IL-2. Notably, ～50% of Tc17 cells also expressed the co-inhibitory molecule CTLA-4, and only a minority (<20%) expressed granzyme B suggesting that these cells possess more of a regulatory than cytotoxic phenotype. After SIV infection, unlike Th17 cells, Tc17 cells were not depleted during the acute phase of infection. However, the frequency of Tc17 cells in SIV-infected macaques with AIDS was lower compared with that in healthy macaques demonstrating the loss of these cells during end-stage disease. Antiretroviral therapy partially restored the frequency of Tc17 and Th17 cells in the colorectal mucosa. Depletion of Tc17 cells was not observed in colorectal mucosa of chronically infected SIV+ sooty mangabeys. In conclusion, our results suggest a role for Tc17 cells in regulating disease progression during pathogenic SIV infection.     

Severe depletion of mucosal CD4+ T cells in AIDS-free simian immunodeficiency virus-infected sooty mangabeys

HIV-infected humans and SIV-infected rhesus macaques experience a rapid and dramatic loss of mucosal CD4+ T cells that is considered to be a key determinant of AIDS pathogenesis. In this study, we show that nonpathogenic SIV infection of sooty mangabeys (SMs), a natural host species for SIV, is also associated with an early, severe, and persistent depletion of memory CD4+ T cells from the intestinal and respiratory mucosa. Importantly, the kinetics of the loss of mucosal CD4+ T cells in SMs is similar to that of SIVmac239-infected rhesus macaques. Although the nonpathogenic SIV infection of SMs induces the same pattern of mucosal target cell depletion observed during pathogenic HIV/SIV infections, the depletion in SMs occurs in the context of limited local and systemic immune activation and can be reverted if virus replication is suppressed by antiretroviral treatment. These results indicate that a profound depletion of mucosal CD4+ T cells is not sufficient per se to induce loss of mucosal immunity and disease progression during a primate lentiviral infection. We propose that, in the disease-resistant SIV-infected SMs, evolutionary adaptation to both preserve immune function with fewer mucosal CD4+ T cells and attenuate the immune activation that follows acute viral infection protect these animals from progressing to AIDS.     

Analysis of the functional capabilities of CD3+CD4-CD8- and CD3+CD4+CD8+ human T cell clones

The functional capabilities of human peripheral blood CD3+CD4-CD8- and CD3+CD4+CD8+ T cell clones were examined. The clones were generated by culturing purified populations of CD3+CD4-CD8- and CD3+CD4+CD8+ T cells at limiting dilution (0.3 cell/well) in the presence of PHA, rIL-2, and irradiated PBMC as feeders. Twelve CD3+CD4-CD8- and 5 CD3+CD4+CD8+ clones were generated. Clonality was documented by analyzing TCR gamma- and beta-chain rearrangement patterns. All CD3+CD4-CD8- clones were stained by the TCR-delta 1 mAb that identifies a framework epitope of the TCR delta-chain, but not by mAb WT31 that identifies the TCR-alpha beta on mature T cells. In contrast, the CD3+CD4+CD8+ clones were all stained by WT31 and not by TCR-delta 1. All 17 clones were screened for various functional activities. Each secreted IL-2, IFN-gamma, and lymphotoxin/TNF-like factors when stimulated with immobilized mAb to CD3 (64.1), albeit in varying quantities. These clones secreted far less IL-2 and IFN-gamma than CD3+CD4+CD8- or CD3+CD4-CD8+ alpha beta expressing clones, but comparable amounts of lymphotoxin/TNF. All clones also functioned as MHC-unrestricted cytotoxic cells. This activity was comparable to that mediated by the CD3+CD4+CD8- or CD3+CD4-CD8+ alpha beta clones. Nine of 12 CD3+CD4-CD8- and 4 of 5 CD3+CD4+CD8+ clones were able to support B cell differentiation when activated by immobilized anti-CD3, but usually not as effectively as the CD3+CD4+CD8- or CD3+CD4-CD8+ alpha beta clones. The differences in the functional capabilities of the various clones could not be accounted for by alterations in the signaling capacity of the CD3 molecular complex as mAb to CD3 induced comparable increases in intracellular free calcium in each clone examined. When clones were stimulated with PWM, each suppressed B cell differentiation supported by mitomycin C-treated fresh CD4+ T lymphocytes. Suppression was dependent on the number of clone cells added to culture, but could be observed with as few as 12,500 cells per microtiter well. Phenotypic analysis of the clones revealed that all expressed CD29, CD11b, and the NKH1 surface Ag. These results demonstrate that the CD3+CD4-CD8- and CD3+CD4+CD8+ T cell clones exhibit many of the functional characteristics of mature T cells, although they produce IL-2 and IFN-gamma and provide help for B cell differentiation less effectively than CD3+CD4+CD8- and CD3+CD4-CD8+ alpha beta T cell clones.     

Depletion of CD8+ cells in sooty mangabey monkeys naturally infected with simian immunodeficiency virus reveals limited role for immune control of virus replication in a natural host species

SIV infection of sooty mangabeys (SMs), a natural host species, does not cause AIDS despite high-level virus replication. In contrast, SIV infection of nonnatural hosts such as rhesus macaques (RMs) induces an AIDS-like disease. The depletion of CD8+ T cells during SIV infection of RMs results in marked increases in plasma viremia, suggesting a key role for CD8+ T cells in controlling levels of SIV replication. To assess the role that CD8+ T cells play in determining the virologic and immunologic features of nonpathogenic SIV infection in SMs, we transiently depleted CD8+ T cells in SIV-infected and uninfected SMs using a CD8alpha-specific Ab (OKT8F) previously used in studies of SIV-infected RMs. Treatment of SMs with the OKT8F Ab resulted in the prompt and profound depletion of CD8+ T cells. However, in contrast to CD8+ cell depleted, SIV-infected RMs, only minor changes in the levels of plasma viremia were observed in most SIV-infected SMs during the period of CD8+ cell deficiency. Those SMs demonstrating greater increases in SIV replication following CD8+ cell depletion also displayed higher levels of CD4+ T cell activation and/or evidence of CMV reactivation, suggesting that an expanded target cell pool rather than the absence of CD8+ T cell control may have been primarily responsible for transient increases in viremia. These data indicate that CD8+ T cells exert a limited influence in determining the levels of SIV replication in SMs and provide additional evidence demonstrating that the absence of AIDS in SIV-infected SMs is not due to the effective control of viral replication by cellular immune responses.