Loss of naïve cells accompanies memory CD4+ T-cell depletion during long-term progression to AIDS in Simian immunodeficiency virus-infected macaques

Human immunodeficiency virus and simian immunodeficiency virus (SIV) induce a slow progressive disease, characterized by the massive loss of memory CD4+ T cells during the acute infection followed by a recovery phase in which virus replication is partially controlled. However, because the initial injury is so severe and virus production persists, the immune system eventually collapses and a symptomatic fatal disease invariably occurs. We have assessed CD4+ T-cell dynamics and disease progression in 12 SIV-infected rhesus monkeys for nearly 2 years. Three macaques exhibiting a rapid progressor phenotype experienced rapid and irreversible loss of memory, but not na?ve, CD4+ T lymphocytes from peripheral blood and secondary lymphoid tissues and died within the first 6 months of virus inoculation. In contrast, SIV-infected conventional progressor animals sustained marked but incomplete depletions of memory CD4+ T cells and continuous activation/proliferation of this T-lymphocyte subset. This was associated with a profound loss of na?ve CD4+ T cells from peripheral blood and secondary lymphoid tissues, which declined at rates that correlated with disease progression. These data suggest that the persistent loss of memory CD4(+)T cells, which are being eliminated by direct virus killing and activation-induced cell death, requires the continuous differentiation of na?ve into memory CD4+ T cells. This unrelenting replenishment process eventually leads to the exhaustion of the na?ve CD4+T-cell pool and the development of disease.     

Naïve blood monocytes suppress T-cell function. A possible mechanism for protection from autoimmunity

In certain disease context, cells of the monocyte/macrophage lineage are known to exhibit T-cell suppressor function. However, whether na?ve monocytes are also able to suppress T-cell responses has not been previously investigated. In this study, we have discovered that CD11b(+)Ly6G(-) mononuclear cells in the blood of na?ve mice are potent suppressors of T-cell proliferation in vitro. The suppression of T-cell proliferation requires cell-cell contact and is partially dependent on nitric oxide production. Following the induction of experimental autoimmune encephalomyelitis in mice, the suppressor function of this blood CD11b(+)Ly6G(-) cell population is impaired. Therefore, blood CD11b(+)Ly6G(-) cells appear to be intrinsically suppressive and may have a key role in maintaining immune homoeostasis. Loss of this suppressive function may contribute to development of autoimmunity.     

Dynamics of CCR5 expression by CD4(+) T cells in lymphoid tissues during simian immunodeficiency virus infection

Early viral replication and profound CD4(+) T-cell depletion occur preferentially in intestinal tissues of macaques infected with simian immunodeficiency virus (SIV). Here we show that a much higher percentage of CD4(+) T cells in the intestine express CCR5 compared with those found in the peripheral blood, spleen, or lymph nodes. In addition, the selectivity and extent of the CD4(+) T-cell loss in SIV infection may depend upon these cells coexpressing CCR5 and having a "memory" phenotype (CD45RA(-)). Following intravenous infection with SIVmac251, memory CD4(+) CCR5(+) T cells were selectively eliminated within 14 days in all major lymphoid tissues (intestine, spleen, and lymph nodes). However, the effect on CD4(+) T-cell numbers was most profound in the intestine, where cells of this phenotype predominate. The CD4(+) T cells that remain after 14 days of infection lacked CCR5 and/or were naive (CD45RA(+)). Furthermore, when animals in the terminal stages of SIV infection (with AIDS) were examined, virtually no CCR5-expressing CD4(+) T cells were found in lymphoid tissues, and all of the remaining CD4(+) T cells were naive and coexpressed CXCR4. These findings suggest that chemokine receptor usage determines which cells are targeted for SIV infection and elimination in vivo.     

Increased loss of CCR5+ CD45RA- CD4+ T cells in CD8+ lymphocyte-depleted Simian immunodeficiency virus-infected rhesus monkeys

Previously we have shown that CD8(+) T cells are critical for containment of simian immunodeficiency virus (SIV) viremia and that rapid and profound depletion of CD4(+) T cells occurs in the intestinal tract of acutely infected macaques. To determine the impact of SIV-specific CD8(+) T-cell responses on the magnitude of the CD4(+) T-cell depletion, we investigated the effect of CD8(+) lymphocyte depletion during primary SIV infection on CD4(+) T-cell subsets and function in peripheral blood, lymph nodes, and intestinal tissues. In peripheral blood, CD8(+) lymphocyte-depletion changed the dynamics of CD4(+) T-cell loss, resulting in a more pronounced loss 2 weeks after infection, followed by a temporal rebound approximately 2 months after infection, when absolute numbers of CD4(+) T cells were restored to baseline levels. These CD4(+) T cells showed a markedly skewed phenotype, however, as there were decreased levels of memory cells in CD8(+) lymphocyte-depleted macaques compared to controls. In intestinal tissues and lymph nodes, we observed a significantly higher loss of CCR5(+) CD45RA(-) CD4(+) T cells in CD8(+) lymphocyte-depleted macaques than in controls, suggesting that these SIV-targeted CD4(+) T cells were eliminated more efficiently in CD8(+) lymphocyte-depleted animals. Also, CD8(+) lymphocyte depletion significantly affected the ability to generate SIV Gag-specific CD4(+) T-cell responses and neutralizing antibodies. These results reemphasize that SIV-specific CD8(+) T-cell responses are absolutely critical to initiate at least partial control of SIV infection.     

Helper-independent, L-selectinlow CD8+ T cells with broad anti-tumor efficacy are naturally sensitized during tumor progression

We recently reported that the CD4(+) T cell subset with low L-selectin expression (CD62L(low)) in tumor-draining lymph nodes (TDLN) can be culture activated and adoptively transferred to eradicate established pulmonary and intracranial tumors in syngeneic mice, even without coadministration of IL-2. We have extended these studies to characterize the small subset of L-selectin(low) CD8(+) T cells naturally present in TDLN of mice bearing weakly immunogenic tumors. Isolated L-selectin(low) CD8(+) T cells displayed the functional phenotype of helper-independent T cells, and when adoptively transferred could consistently eradicate, like L-selectin(low) CD4(+) T cells, both established pulmonary and intracranial tumors without coadministration of exogenous IL-2. Whereas adoptively transferred L-selectin(low) CD4(+) T cells were more potent on a cell number basis for eradicating 3-day intracranial and s.c. tumors, L-selectin(low) CD8(+) T cells were more potent against advanced (10-day) pulmonary metastases. Although the presence of CD4(+) T cells enhanced generation of L-selectin(low) CD8(+) effector T cells, the latter could also be obtained from CD4 knockout mice or normal mice in vivo depleted of CD4(+) T cells before tumor sensitization. Culture-activated L-selectin(low) CD8(+) T cells did not lyse relevant tumor targets in vitro, but secreted IFN-gamma and GM-CSF when specifically stimulated with relevant tumor preparations. These data indicate that even without specific vaccine maneuvers, progressive tumor growth leads to independent sensitization of both CD4(+) and CD8(+) anti-tumor T cells in TDLN, phenotypically L-selectin(low) at the time of harvest, each of which requires only culture activation to unmask highly potent stand-alone effector function.     

Experimental Trypanosoma cruzi infection alters the shaping of the central and peripheral T-cell repertoire

We investigated the thymic and peripheral T-lymphocyte subsets in BALB/c mice undergoing acute or chronic Trypanosoma cruzi infection, in terms of expression of particular Vbeta rearrangements of the T-cell receptor. We first confirmed the severe depletion of CD4(+)CD8(+) thymocytes following acute T. cruzi infection. By contrast, the numbers of CD4(+)CD8(+) cells in subcutaneous lymph nodes increased up to 16 times. In subcutaneous lymph nodes, we found CD4(+)CD8(+) cells that expressed prohibited segments TCRVbeta5 and TCRVbeta12 (which are physiologically deleted in the thymus of BALB/c mice), as did some mature single-positive cells (CD4(+)CD8(-) and CD4(-)CD8(+)). In the thymus of infected animals, although higher numbers of immature cells bearing such Vbeta segments were seen, they were no longer detected in the mature single-positive stage, suggesting that negative selection occurs normally. We also found increased numbers of cells bearing the potentially autoreactive phenotype TCRVbeta5(+) and TCRVbeta12(+) in T-lymphocyte subsets from subcutaneous lymph nodes of T. cruzi chronically infected mice. In conclusion, our data indicate that immature T lymphocytes bearing prohibited TCRVbeta segments leave the thymus and gain the lymph nodes, where they further differentiate into mature CD4(+) or CD8(+) cells. Conjointly, these findings show changes in the shaping of the central and peripheral T-cell repertoire in both acute and chronic phases of murine T. cruzi infection. The release of potentially autoreactive T cells in the periphery of the immune system may contribute to the autoimmune process found in both murine and human Chagas' disease.     

Compromised influenza virus-specific CD8(+)-T-cell memory in CD4(+)-T-cell-deficient mice

The primary influenza A virus-specific CD8(+)-T-cell responses measured by tetramer staining of spleen, lymph node, and bronchoalveolar lavage (BAL) lymphocyte populations were similar in magnitude for conventional I-A(b+/+) and CD4(+)-T-cell-deficient I-A(b-/-) mice. Comparable levels of virus-specific cytotoxic-T-lymphocyte activity were detected in the inflammatory exudate recovered by BAL following challenge. However, both the size of the memory T-cell pool and the magnitude of the recall response in the lymphoid tissues (but not the BAL specimens) were significantly diminished in mice lacking the CD4(+) subset. Also, the rate of virus elimination from the infected respiratory tract slowed at low virus loads following challenge of na?ve and previously immunized I-A(b-/-) mice. Thus, though the capacity to mediate the CD8(+)-T-cell effector function is broadly preserved in the absence of concurrent CD4(+)-T-cell help, both the maintenance and recall of memory are compromised and the clearance of residual virus is delayed. These findings are consistent with mathematical models that predict virus-host dynamics in this, and other, models of infection.     

Simian immunodeficiency virus infection induces severe loss of intestinal central memory T cells which impairs CD4+ T-cell restoration during antiretroviral therapy

BACKGROUND: Simian immunodeficiency virus (SIV) infection leads to severe loss of intestinal CD4(+) T cells and, as compared to peripheral blood, restoration of these cells is slow during antiretroviral therapy (ART). Mechanisms for this delay have not been examined in context of which specific CD4(+) memory subsets or lost and fail to regenerate during ART. METHODS: Fifteen rhesus macaques were infected with SIV, five of which received ART (FTC/PMPA) for 30 weeks. Viral loads were measured by real-time PCR. Flow cytometric analysis determined changes in T-cell subsets and their proliferative state. RESULTS: Changes in proliferative CD4(+) memory subsets during infection accelerated their depletion. This reduced the central memory CD4(+) T-cell pool and contributed to slow CD4(+) T-cell restoration during ART. CONCLUSION: There was a lack of restoration of the CD4(+) central memory and effector memory T-cell subsets in gut-associated lymphoid tissue during ART, which may contribute to the altered intestinal T-cell homeostasis in SIV infection.     

Quantitative analysis of the acute and long-term CD4(+) T-cell response to a persistent gammaherpesvirus

The murine gammaherpesvirus 68 (MHV-68) replicates in respiratory epithelial cells, where it establishes a persistent, latent infection limited predominantly to B lymphocytes. The virus-specific CD4(+) T-cell response in C57BL/6 mice challenged intranasally with MHV-68 is detected first in the mediastinal lymph nodes and then in the cervical lymph nodes and the spleen. The numbers of MHV-68-specific CD4(+) T cells generated in congenic mice homozygous for disruption of the beta2-microglobulin gene tended to be higher, indicating that the absence of the CD8(+) set in this group resulted in a compensatory response. The peak frequency within the splenic CD4(+) T-cell population may reach 1:50 in the acute response; it then drops to 1:400 to 1:500 within 4 months and stays at that level in the very long term. Sorting for L-selectin (CD62L) expression established that all virus-specific CD4(+) T cells were initially CD62Llow, with >80% maintaining that phenotype for the next 14 months. The overall conclusion is that MHV-68-specific CD4(+) T cells remain activated (CD62Llow) and at a stable frequency in the face of persistent infection.     

Pathogenesis of mousepox in H-2(d) mice: evidence for MHC class I-restricted CD8(+) and MHC class II-restricted CD4(+) CTL antiviral activity in the lymph nodes, spleen and skin, but not in the conjunctivae.

Genetically sensitive mice (i.e. H-2(d) haplotype) infected with a natural mouse pathogen named ectromelia virus (EV) can develop a mousepox. Virus replicates well in the skin, next in the draining lymph nodes (DLNs) and then in the spleen and liver, where it may induce extensive necrosis with strong inflammatory reaction. It is well known from the studies defined on some other viruses that a correlation, functional link and powerful help exist between MHC class I-restricted CD8(+) and MHC class II-restricted CD4(+) virus-specific cytotoxic T lymphocytes (CTLs). However, in the case of mousepox the role of CD4(+) CTLs is still controversial and some reports support the notion that induction of EV-specific CD4(+) CTLs is nonessential for the generation of virus-specific immune response. Consequently, this study was designed to evaluate EV-specific CD8(+) and CD4(+) CTL activity in the DLNs, spleen, skin and conjunctivae of BALB/c (H-2(d)) mice at 7 and 14 days p.i. with Moscow strain of EV. By using bulk cytotoxicity assay and immunosurgery of effector T cells with mAb specific for CD4(+) and/or CD8(+) T cells our data show that EV-specific CD8(+) CTLs predominated in DLNs and spleen at 7 days (67 and 66% of total CTLs, respectively) and 14 days p.i. (63 and 69% of total CTLs, respectively). In contrast, we found that EV clearance from the cutaneous lesions during mousepox is CD4(+) CTL-dependent at 7 days p.i. (59% of total CTLs), whereas at 14 days p.i. CD8(+) CTLs predominated in the epidermis, accounting for 72% of the total EV-specific CTLs. Our studies showed that the population of EV-specific CTLs is heterogeneous and contains cells of both phenotypes: CD8(+) and CD4(+). However, these effector cells did not express a similar tendency in cytotoxic activity in the DLNs, spleen and skin in comparison to the conjunctivae where EV-specific CD8(+) and CD4(+) CTLs were not detected at 7 days p.i. and at peak of mousepox conjunctivitis (14 days p.i.). Our results are discussed in terms of the value of EV to study antiviral CTL responses in the genetically susceptible host.     

Vaccines based on novel adeno-associated virus vectors elicit aberrant CD8+ T-cell responses in mice

We recently discovered an expanded family of adeno-associated viruses (AAVs) that show promise as improved gene therapy vectors. In this study we evaluated the potential of vectors based on several of these novel AAVs as vaccine carriers for human immunodeficiency virus type 1 Gag. Studies with mice indicated that vectors based on AAV type 7 (AAV7), AAV8, and AAV9 demonstrate improved immunogenicity in terms of Gag CD8(+) T-cell and Gag antibody responses. The quality of these antigen-specific responses was evaluated in detail for AAV2/8 vectors and compared to results with an adenovirus vector expressing Gag (AdC7). AAV2/8 produced a vibrant CD8(+) T-cell effector response characterized by coexpression of gamma interferon and tumor necrosis factor alpha as well as in vivo cytolytic activity. No CD8(+) T-cell response generated by any of the AAVs was effectively boosted with AdC7, a result consistent with the finding of a relative lack of cells expressing interleukin-2 (IL-2) or a central memory phenotype at 3 months after the prime. The primary response to an AdC7 vaccine differed from that generated by AAVs in that the peak effector response evolved into populations of Gag-specific T cells expressing high levels of cytokines, including IL-2, and with effector memory and central memory phenotypes. A number of mechanisms could be considered to explain the aberrant activation of CD8(+) T cells by AAV, including insufficient inflammatory responses, CD4 help, and/or chronic antigen expression and T-cell exhaustion. Interestingly, the B-cell response to AAV-encoded Gag was quite vibrant and easily boosted with AdC7.     

Memory CD8+ T cells provide an early source of IFN-gamma

During the non-Ag-specific early phase of infection, IFN-gamma is believed to be primarily provided by NK and NKT cells in response to pathogen-derived inflammatory mediators. To test whether other cell types were involved in early IFN-gamma release, IFN-gamma-producing cells were visualized in spleens and lymph nodes of LPS-injected mice. In addition to NK and NKT cells, IFN-gamma was also detected in a significant fraction of CD8(+) T cells. CD8(+) T cells represented the second major population of IFN-gamma-producing cells in the spleen ( approximately 30%) and the majority of IFN-gamma(+) cells in the lymph nodes ( approximately 70%). LPS-induced IFN-gamma production by CD8(+) T cells was MHC class I independent and was restricted to CD44(high) (memory phenotype) cells. Experiments performed with C3H/HeJ (LPS-nonresponder) mice suggested that CD8(+) T cells responded to LPS indirectly through macrophage/dendritic cell-derived IFN-alpha/beta, IL-12, and IL-18. IFN-gamma was also detected in memory CD8(+) T cells from mice injected with type I IFN or with poly(I:C), a synthetic dsRNA that mimics early activation by RNA viruses. Taken together, these results suggest that in response to bacterial and viral products, memory T cells may contribute to innate immunity by providing an early non-Ag-specific source of IFN-gamma.     

Suppressor of cytokine signaling 1 stringently regulates distinct functions of IL-7 and IL-15 in vivo during T lymphocyte development and homeostasis

SOCS1(-/-) mice accumulate within the thymus and periphery CD8(+) lymphocytes that express memory cell markers and display heightened in vitro responses to common gamma-chain cytokines. To investigate whether dysregulated homeostasis of T lymphocytes and acquisition of memory phenotype by CD8(+) cells in SOCS1(-/-) mice were mediated by IL-7 and/or IL-15 in vivo, we have generated SOCS1(-/-)IL-7(-/-), SOCS1(-/-)IL-15(-/-) and SOCS1(-/-)IL-7(-/-)IL-15(-/-) mice. We observed that in mice lacking SOCS1, either IL-7 or IL-15 skewed thymocyte development toward CD8 lineage, whereas IL-15 is the principal mediator of dysregulated homeostasis in the periphery. Homeostatic proliferation of SOCS1(-/-) CD8(+) lymphocytes in Rag1(-/-), Rag1(-/-)IL-7(-/-), Rag1(-/-)IL-15(-/-), and Rag1(-/-)IL-7(-/-)IL-15(-/-) mice showed that SOCS1 deficiency did not overcome the requirement for IL-7 and IL-15 to sustain homeostatic expansion. Differential expression of memory phenotype markers CD44, CD122, and Ly6C by SOCS1(-/-)IL-15(-/-) CD8(+) lymphocytes suggest that multiple signals contributed to the memory cell differentiation program. To address whether increased IL-15 responsiveness of SOCS1(-/-) CD8(+) lymphocytes required prior TCR sensitization, we generated SOCS1(-/-) H-Y TCR transgenic (Tg) mice. Using female SOCS1(-/-) H-Y TCR(tg) mice in Rag1(+/+) and Rag1(-/-) backgrounds, we show that acquisition of the memory phenotype by SOCS1-deficient CD8(+) lymphocytes did not require prior antigenic stimulation, but required the presence of activated T cells. SOCS1 deficiency accelerated the maturation of CD8 single-positive thymocytes expressing Tg TCR, but did not compromise negative selection in HY-TCR(tg) males. Our findings illustrate distinct functions for IL-7 and IL-15 in T lymphocyte development and homeostasis, and stringent regulation of these processes by SOCS1.     

Immune evasion by Yersinia enterocolitica: differential targeting of dendritic cell subpopulations in vivo

CD4(+) T cells are essential for the control of Yersinia enterocolitica (Ye) infection in mice. Ye can inhibit dendritic cell (DC) antigen uptake and degradation, maturation and subsequently T-cell activation in vitro. Here we investigated the effects of Ye infection on splenic DCs and T-cell proliferation in an experimental mouse infection model. We found that OVA-specific CD4(+) T cells had a reduced potential to proliferate when stimulated with OVA after infection with Ye compared to control mice. Additionally, proliferation of OVA-specific CD4(+) T cells was markedly reduced when cultured with splenic CD8α(+) DCs from Ye infected mice in the presence of OVA. In contrast, T-cell proliferation was not impaired in cultures with CD4(+) or CD4(-)CD8α(-) DCs isolated from Ye infected mice. However, OVA uptake and degradation as well as cytokine production were impaired in CD8α(+) DCs, but not in CD4(+) and CD4(-)CD8α(-) DCs after Ye infection. Pathogenicity factors (Yops) from Ye were most frequently injected into CD8α(+) DCs, resulting in less MHC class II and CD86 expression than on non-injected CD8α(+) DCs. Three days post infection with Ye the number of splenic CD8α(+) and CD4(+) DCs was reduced by 50% and 90%, respectively. The decreased number of DC subsets, which was dependent on TLR4 and TRIF signaling, was the result of a faster proliferation and suppressed de novo DC generation. Together, we show that Ye infection negatively regulates the stimulatory capacity of some but not all splenic DC subpopulations in vivo. This leads to differential antigen uptake and degradation, cytokine production, cell loss, and cell death rates in various DC subpopulations. The data suggest that these effects might be caused directly by injection of Yops into DCs and indirectly by affecting the homeostasis of CD4(+) and CD8α(+) DCs. These events may contribute to reduced T-cell proliferation and immune evasion of Ye.     

Arginase-dependent suppression by CpG-ODN plus IFA-induced splenic myeloid CD11b(+)Gr1(+) cells

The ability of synthetic oligodeoxynucleotides containing unmethylated cytosine guanine motifs (CpG-ODN) to induce both stimulatory and counter-regulatory responses offers novel opportunities for using these molecules as immunomodulatory agents in different therapeutic strategies. Here, we investigated the potential of CpG-ODN to activate the arginase (ARG) enzyme in vivo and focused on the consequences of this activation in T-cell proliferation. Challenging mice subcutaneously with CpG-ODN emulsified in incomplete Freund's adjuvant (IFA) induced ARG and reduced T-cell proliferation associated with CD3ζ chain downregulation. Interestingly, impaired T-cell expansion correlated with elevated levels of CD11b(+)Gr1(+) myeloid cells localized near T-cell areas in the spleen. In addition, purified CD11b(+) cells obtained from the spleen of CpG-ODN+IFA-treated mice exhibited increased ARG activity and ARG I expression along with an augmented [(3)H]-L-arginine uptake. CD11b(+) myeloid cells significantly suppressed T-cell proliferation and CD3ζ chain expression induced by a polyclonal stimulus. Furthermore, these effects could be recovered by the addition of excess L-arginine or by treatment of CD11b(+) cells with a specific ARG inhibitor. This study provides a novel evidence that CpG-ODN+IFA are able to induce splenic CD11b(+) cells with ARG activity, with this population being responsible for the impaired T-cell proliferation observed after the treatment with CpG-ODN+IFA. These results underscore a key role of CpG-ODN on ARG activity in vivo and add support to the growing body of evidence in favor of a counter-regulatory role for CpG-ODN in an immune response.     

T-cell subsets that harbor human immunodeficiency virus (HIV) in vivo: implications for HIV pathogenesis

Identification of T-cell subsets that are infected in vivo is essential to understanding the pathogenesis of human immunodeficiency virus (HIV) disease; however, this goal has been beset with technical challenges. Here, we used polychromatic flow cytometry to sort multiple T-cell subsets to 99.8% purity, followed by quantitative PCR to quantify HIV gag DNA directly ex vivo. We show that resting memory CD4(+) T cells are the predominantly infected cells but that terminally differentiated memory CD4(+) T cells contain 10-fold fewer copies of HIV DNA. Memory CD8(+) T cells can also be infected upon upregulation of CD4; however, this is infrequent and HIV-specific CD8(+) T cells are not infected preferentially. Na?ve CD4(+) T-cell infection is rare and principally confined to those peripheral T cells that have proliferated. Furthermore, the virus is essentially absent from na?ve CD8(+) T cells, suggesting that the thymus is not a major source of HIV-infected T cells in the periphery. These data illuminate the underlying mechanisms that distort T-cell homeostasis in HIV infection.     

CD8(+) T-cell homeostasis after infection: setting the 'curve'

Antigen (Ag)-specific CD8(+) T-cell responses exhibit remarkably similar kinetics after different types of infection. Starting from levels that are virtually undetectable in vivo, pathogen-specific na?ve CD8(+) T cells are precisely regulated to go through rapid expansion and contraction (death) phases, achieving memory levels of Ag-specific CD8(+) T cells that are maintained for the life of the host. However, the exact mechanisms used to achieve appropriate and reproducible CD8(+) T-cell homeostasis in response to diverse pathogens remain to be determined. The possibility that early events after infection regulate major features of Ag-specific CD8(+) T-cell homeostasis will be discussed here.     

Failure of CD4 T-cells to respond to liver-derived antigen and to provide help to CD8 T-cells

CD4 T-cell help is required for the induction of efficient CD8 T-cells responses and the generation of memory cells. Lack of CD4 T-cell help may contribute to an exhausted CD8 phenotype and viral persistence. Little is known about priming of CD4 T-cells by liver-derived antigen. We used TF-OVA mice expressing ovalbumin in hepatocytes to investigate CD4 T-cell priming by liver-derived antigen and the impact of CD4 T-cell help on CD8 T-cell function. Naïve and effector CD4 T-cells specific for ovalbumin were transferred into TF-OVA mice alone or together with naïve ovalbumin-specific CD8 T-cells. T-cell activation and function were analyzed. CD4 T-cells ignored antigen presented by liver antigen-presenting cells (APCs) in vitro and in vivo but were primed in the liver-draining lymph node and the spleen. No priming occurred in the absence of bone-marrow derived APCs capable of presenting ovalbumin in vivo. CD4 T-cells primed in TF-OVA mice displayed defective Th1-effector function and caused no liver damage. CD4 T-cells were not required for the induction of hepatitis by CD8 T-cells. Th1-effector but not naïve CD4 T-cells augmented the severity of liver injury caused by CD8 T-cells. Our data demonstrate that CD4 T-cells fail to respond to liver-derived antigen presented by liver APCs and develop defective effector function after priming in lymph nodes and spleen. The lack of CD4 T-cell help may be responsible for insufficient CD8 T-cell function against hepatic antigens.     

Defective Signaling in a Subpopulation of CD4+ T Cells in the Absence of Ca2+/Calmodulin-Dependent Protein Kinase IV

Ca(2+)/calmodulin-dependent protein kinase IV-deficient (CaMKIV(-/-)) mice have been used to investigate the role of this enzyme in CD4(+) T cells. We identify a functional defect in a subpopulation of CD4(+) T cells, characterized by a cell surface marker profile usually found on memory phenotype CD4(+) T cells. Upon T-cell receptor engagement, the mutant cells produce diminished levels of interleukin-2 (IL-2), IL-4, and gamma interferon protein and mRNA. The defect is secondary to an inability to phosphorylate CREB and to induce CREB-dependent immediate-early genes, including c-jun, fosB, fra2, and junB, which are required for cytokine gene induction. In contrast, stimulated naive CD4(+) T cells from CaMKIV(-/-) mice show normal CREB phosphorylation, induction of immediate-early genes, and cytokine production. Thus, in addition to defining an important signaling role for CaMKIV in a subpopulation of T cells, we identify differential signaling requirements for cytokine production between naive T cells and T cells that express cell surface markers characteristic of the memory phenotype.     

PSGL-1 regulates the migration and proliferation of CD8(+) T cells under homeostatic conditions

P-selectin glycoprotein ligand-1 (PSGL-1), a heavily glycosylated sialomucin expressed on most leukocytes, has dual function as a selectin ligand for leukocyte rolling on vascular selectins expressed in inflammation and as a facilitator of resting T cell homing into lymphoid organs. In this article, we document disturbances in T cell homeostasis present in PSGL-1(null) mice. Naive CD4(+) and CD8(+) T cell frequencies were profoundly reduced in blood, whereas T cell numbers in lymph nodes and spleen were at or near normal levels. Although PSGL-1(null) T cells were less efficient at entering lymph nodes, they also remained in lymph nodes longer than PSGL-1(+/+) T cells, suggesting that PSGL-1 supports T cell egress. In addition, PSGL-1(null) CD8(+) T cell proliferation was observed under steady-state conditions and PSGL-1(null) CD8(+) T cells were found to be hyperresponsive to homeostatic cytokines IL-2, IL-4, and IL-15. Despite these disturbances in T cell homeostasis, PSGL-1(null) mice exhibited a normal acute response (day 8) to lymphocytic choriomeningitis virus infection but generated an increased frequency of memory T cells (day 40). Our observations demonstrate a novel pleiotropic influence of PSGL-1 deficiency on several aspects of T cell homeostasis that would not have been anticipated based on the mild phenotype of PSGL-1(null) mice. These potentially offsetting effects presumably account for the near-normal cellularity seen in lymph nodes of PSGL-1(null) mice.