T cell reactivity against mycolyl transferase antigen 85 of M. tuberculosis in HIV-TB coinfected subjects and in AIDS patients suffering from tuberculosis and nontuberculous mycobacterial infections.

The mycolyl transferase antigen 85 complex is a major secreted protein family from mycobacterial culture filtrate, demonstrating powerful T cell stimulatory properties in most HIV-negative, tuberculin-positive volunteers with latent M.tuberculosis infection and only weak responses in HIV-negative tuberculosis patients. Here, we have analyzed T cell reactivity against PPD and Ag85 in HIV-infected individuals, without or with clinical symptoms of tuberculosis, and in AIDS patients with disease caused by nontuberculous mycobacteria. Whereas responses to PPD were not significantly different in HIV-negative and HIV-positive tuberculin-positive volunteers, responses to Ag85 were significantly decreased in the HIV-positive (CDC-A and CDC-B) group. Tuberculosis patients demonstrated low T cell reactivity against Ag85, irrespective of HIV infection, and finally AIDS patients suffering from NTM infections were completely nonreactive to Ag85. A one-year follow-up of twelve HIV-positive tuberculin-positive individuals indicated a decreased reactivity against Ag85 in patients developing clinical tuberculosis, highlighting the protective potential of this antigen.

KAP1 regulates gene networks controlling T-cell development and responsiveness.

Chromatin remodeling at specific genomic loci controls lymphoid differentiation. Here, we investigated the role played in this process by Kruppel-associated box (KRAB)-associated protein 1 (KAP1), the universal cofactor of KRAB-zinc finger proteins (ZFPs), a tetrapod-restricted family of transcriptional repressors. T-cell-specific Kap1-deleted mice displayed a significant expansion of immature thymocytes, imbalances in CD4(+)/CD8(+) cell ratios, and altered responses to TCR and TGFβ stimulation when compared to littermate KAP1 control mice. Transcriptome and chromatin studies revealed that KAP1 binds T-cell-specific cis-acting regulatory elements marked by the H3K9me3 repressive mark and enriched in Ikaros/NuRD complexes. Also, KAP1 directly controls the expression of several genes involved in TCR and cytokine signaling. Among these, regulation of FoxO1 seems to play a major role in this system. Likely responsible for tethering KAP1 to at least part of its genomic targets, a small number of KRAB-ZFPs are selectively expressed in T-lymphoid cells. These results reveal the so far unsuspected yet important role of KAP1-mediated epigenetic regulation in T-lymphocyte differentiation and activation.

Long-term safety and effectiveness of ritonavir, nelfinavir, and lopinavir/ritonavir in antiretroviral-experienced HIV-infected children.

AIM: To evaluate the long-term safety and effectiveness of ritonavir, nelfinavir, and lopinavir/ritonavir in antiretroviral-experienced, initially protease inhibitor (PI)-naive, human immunodeficiency virus (HIV)-1-infected children. METHODS: HIV-1-infected children enrolled in the Swiss Mother and Child HIV Cohort Study were eligible for this observational cohort study if they received at least 1 PI of interest between March 1996 and October 2003: ritonavir, nelfinavir, or lopinavir/ritonavir. Data regarding demographics, clinical disease and antiretroviral treatment history, HIV-1 RNA copies/mL, CD4 T-cell counts [absolute (cells/microL) and percentages (%)], adverse events, clinical laboratory values, reasons for discontinuation of PIs, and concomitant medications were extracted from the database for PI-naive (first-line) and PI-experienced (second- or higher-line) PI use. RESULTS: The total duration of ritonavir, nelfinavir, and lopinavir/ritonavir use for 133 HIV-1-infected children was 163.8, 235.0, and 46.1 patient-years, respectively. In an on-treatment analysis, first-line therapy with any of the PIs significantly reduced HIV-1 concentrations and increased CD4 T-cell counts and percentages from baseline throughout the 288-week study (P <or= 0.05) for ritonavir and nelfinavir and throughout 84 weeks of use for lopinavir/ritonavir, which was introduced into treatment more recently. All PIs investigated were most effective in PI-naive children. Thirteen PI-associated toxicities occurred requiring treatment changes or interruptions (neurologic symptoms, n = 2; pancreatitis, n = 1; allergic reactions, n = 4; visual symptoms, n = 3; and hyperlipidemia, n = 3). CONCLUSIONS: Long-term PI-based therapy seems to be safe and to result in durable virologic and immunologic effectiveness in HIV-1-infected antiretroviral-experienced children.

Genetic deficiency of tartrate-resistant acid phosphatase associated with skeletal dysplasia, cerebral calcifications and autoimmunity.

Vertebral and metaphyseal dysplasia, spasticity with cerebral calcifications, and strong predisposition to autoimmune diseases are the hallmarks of the genetic disorder spondyloenchondrodysplasia. We mapped a locus in five consanguineous families to chromosome 19p13 and identified mutations in ACP5, which encodes tartrate-resistant phosphatase (TRAP), in 14 affected individuals and showed that these mutations abolish enzyme function in the serum and cells of affected individuals. Phosphorylated osteopontin, a protein involved in bone reabsorption and in immune regulation, accumulates in serum, urine and cells cultured from TRAP-deficient individuals. Case-derived dendritic cells exhibit an altered cytokine profile and are more potent than matched control cells in stimulating allogeneic T cell proliferation in mixed lymphocyte reactions. These findings shed new light on the role of osteopontin and its regulation by TRAP in the pathogenesis of common autoimmune disorders.

Hepatitis E Virus seroprevalence and chronic infections in patients with HIV, Switzerland.

We screened 735 HIV-infected patients in Switzerland with unexplained alanine aminotransferase elevation for hepatitis E virus (HEV) immunoglobulin G. Although HEV seroprevalence in this population is low (2.6%), HEV RNA can persist in patients with low CD4 cell counts. Findings suggest chronic HEV infection should be considered as a cause of persistent alanine aminotransferase elevation.

Induction of potent antitumor CTL responses by recombinant vaccinia encoding a melan-A peptide analogue.

There is considerable interest in the development of vaccination strategies that would elicit strong tumor-specific CTL responses in cancer patients. One strategy consists of using recombinant viruses encoding amino acid sequences corresponding to natural CTL-defined peptide from tumor Ags as immunogens. However, studies with synthetic tumor antigenic peptides have demonstrated that introduction of single amino acid substitutions may dramatically increase their immunogenicity. In this study we have used a well-defined human melanoma tumor Ag system to test the possibility of translating the immunological potency of synthetic tumor antigenic peptide analogues into recombinant vaccinia viruses carrying constructs with the appropriate nucleotide substitutions. Our results indicate that the use of a mutated minigene construct directing the expression of a modified melanoma tumor Ag leads to improved Ag recognition and, more importantly, to enhanced immunogenicity. Thus, recombinant vaccinia viruses containing mutated minigene sequences may lead to new strategies for the induction of strong tumor-specific CTL responses in cancer patients.

Changing responsiveness to chemokines allows medullary plasmablasts to leave lymph nodes.

During T cell-dependent antibody responses lymph node B cells differentiate either to plasmablasts that grow in the medullary cords, or to blasts that proliferate in follicles forming germinal centers. Many plasmablasts differentiate to plasma cells locally, but some leave the medullary cords and migrate to downstream lymph nodes. To assess the basis for this migration, changes in the responsiveness of B cells to a range of chemokines have been studied as they differentiate. Naive B cells express high levels of CCR6, CCR7, CXCR4 and CXCR5. When activated B cells grow in follicles the expression of these chemokine receptors and the responsiveness to the respective chemokines is retained. During the extrafollicular response, plasmablast expression of CXCR5 and responsiveness to B-lymphocyte chemoattractant (CXCR5) as well as to secondary lymphoid tissue chemokine (CCR7) and stromal cell-derived factor (SDF)-1 (CXCR4) are lost while a weak response towards the CCR6 chemokine LARC is maintained. Despite losing responsiveness to SDF-1, extrafollicular plasmablasts still express high levels of CXCR4 on the cell surface. These results suggest that the combined loss of chemokine receptor expression and of chemokine responsiveness may be a necessary prerequisite for cells to migrate to the medullary cords and subsequently enter the efferent lymph.

Theileria parva-transformed T cells show enhanced resistance to Fas/Fas ligand-induced apoptosis.

Lymphocyte homeostasis is regulated by mechanisms that control lymphocyte proliferation and apoptosis. Activation-induced cell death is mediated by the expression of death ligands and receptors, which, when triggered, activate an apoptotic cascade. Bovine T cells transformed by the intracellular parasite Theileria parva proliferate in an uncontrolled manner and undergo clonal expansion. They constitutively express the death receptor Fas and its ligand, FasL but do not undergo apoptosis. Upon elimination of the parasite from the host cell by treatment with a theilericidal drug, cells become increasingly sensitive to Fas/FasL-induced apoptosis. In normal T cells, the sensitivity to death receptor killing is regulated by specific inhibitor proteins. We found that anti-apoptotic proteins such as cellular (c)-FLIP, which functions as a catalytically inactive form of caspase-8, and X-chromosome-linked inhibitor of apoptosis protein (IAP) as well as c-IAP, which can block downstream executioner caspases, are constitutively expressed in T. parva-transformed T cells. Expression of these proteins is rapidly down-regulated upon parasite elimination. Antiapoptotic proteins of the Bcl-2 family such as Bcl-2 and Bcl-x(L) are also expressed but, in contrast to c-FLIP, c-IAP, and X-chromosome-linked IAP, do not appear to be tightly regulated by the presence of the parasite. Finally, we show that, in contrast to the situation in tumor cells, the phosphoinositide 3-kinase/Akt pathway is not essential for c-FLIP expression. Our findings indicate that by inducing the expression of antiapoptotic proteins, T. parva allows the host cell to escape destruction by homeostatic mechanisms that would normally be activated to limit the continuous expansion of a T cell population.

Efficient T cell activation requires an optimal dwell-time of interaction between the TCR and the pMHC complex.

Cytotoxic T cell (CTL) activation by antigen requires the specific detection of peptide-major histocompatibility class I (pMHC) molecules on the target-cell surface by the T cell receptor (TCR). We examined the effect of mutations in the antigen-binding site of a Kb-restricted TCR on T cell activation, antigen binding and dissociation from antigen.These parameters were also examined for variants derived from a Kd-restricted peptide that was recognized by a CTL clone. Using these two independent systems, we show that T cell activation can be impaired by mutations that either decrease or increase the binding half-life of the TCR-pMHC interaction. Our data indicate that efficient T cell activation occurs within an optimal dwell-time range of TCR-pMHC interaction. This restricted dwell-time range is consistent with the exclusion of either extremely low or high affinity T cells from the expanded population during immune responses.

A Role for cis Interaction between the Inhibitory Ly49A receptor and MHC class I for natural killer cell education.

Natural killer (NK) cells show enhanced functional competence when they express inhibitory receptors specific for inherited major histocompatibility complex class I (MHC-I) molecules. Current models imply that NK cell education requires an interaction of inhibitory receptors with MHC-I expressed on other cells. However, the inhibitory Ly49A receptor can also bind MHC-I ligand on the NK cell itself (in cis). Here we describe a Ly49A variant, which can engage MHC-I expressed on other cells but not in cis. Even though this variant inhibited NK cell effector function, it failed to educate NK cells. The association with MHC-I in cis sequestered wild-type Ly49A, and this was found to relieve NK cells from a suppressive effect of unengaged Ly49A. These data explain how inhibitory MHC-I receptors can facilitate NK cell activation. They dissociate classical inhibitory from educating functions of Ly49A and suggest that cis interaction of Ly49A is necessary for NK cell education.

BAFF, APRIL and their receptors: structure, function and signaling.

BAFF, APRIL and their receptors play important immunological roles, especially in the B cell arm of the immune system. A number of splice isoforms have been described for both ligands and receptors in this subfamily, some of which are conserved between mouse and human, while others are species-specific. Structural and mutational analyses have revealed key determinants of receptor-ligand specificity. BAFF-R has a strong selectivity for BAFF; BCMA has a higher affinity for APRIL than for BAFF, while TACI binds both ligands equally well. The molecular signaling events downstream of BAFF-R, BCMA and TACI are still incompletely characterized. Survival appears to be mediated by upregulation of Bcl-2 family members through NF-kappaB activation, degradation of the pro-apototic Bim protein, and control of subcellular localization of PCKdelta. Very little is known about other signaling events associated with receptor engagement by BAFF and APRIL that lead for example to B cell activation or to CD40L-independent Ig switch.

Dramatic influence of V beta gene polymorphism on an antigen-specific CD8+ T cell response in vivo.

According to recent crystallographic studies, the TCR-alpha beta contacts MHC class I-bound antigenic peptides via the polymorphic V gene-encoded complementarity-determining region 1 beta (CDR1 beta) and the hypervariable (D)J-encoded CDR3 beta and CDR3 alpha domains. To evaluate directly the relative importance of CDR1 beta polymorphism on the fine specificity of T cell responses in vivo, we have taken advantage of congenic V beta a and V beta b mouse strains that differ by a CDR1 polymorphism in the V beta 10 gene segment. The V beta 10-restricted CD8+ T cell response to a defined immunodominant epitope was dramatically reduced in V beta a compared with V beta b mice, as measured either by the expansion of V beta 10+ cells or by the binding of MHC-peptide tetramers. These data indicate that V beta polymorphism has an important impact on TCR-ligand binding in vivo, presumably by modifying the affinity of CDR1 beta-peptide interactions.

Positive and negative regulation of T cell responses by fibroblastic reticular cells within paracortical regions of lymph nodes.

Fibroblastic reticular cells (FRC) form the structural backbone of the T cell rich zones in secondary lymphoid organs (SLO), but also actively influence the adaptive immune response. They provide a guidance path for immigrating T lymphocytes and dendritic cells (DC) and are the main local source of the cytokines CCL19, CCL21, and IL-7, all of which are thought to positively regulate T cell homeostasis and T cell interactions with DC. Recently, FRC in lymph nodes (LN) were also described to negatively regulate T cell responses in two distinct ways. During homeostasis they express and present a range of peripheral tissue antigens, thereby participating in peripheral tolerance induction of self-reactive CD8(+) T cells. During acute inflammation T cells responding to foreign antigens presented on DC very quickly release pro-inflammatory cytokines such as interferon γ. These cytokines are sensed by FRC which transiently produce nitric oxide (NO) gas dampening the proliferation of neighboring T cells in a non-cognate fashion. In summary, we propose a model in which FRC engage in a bidirectional crosstalk with both DC and T cells to increase the efficiency of the T cell response. However, during an acute response, FRC limit excessive expansion and inflammatory activity of antigen-specific T cells. This negative feedback loop may help to maintain tissue integrity and function during rapid organ growth.

CD4(+) T cell count decreases by ethnicity among untreated patients with HIV infection in South Africa and Switzerland.

BACKGROUND: Estimates of the decrease in CD4(+) cell counts in untreated patients with human immunodeficiency virus (HIV) infection are important for patient care and public health. We analyzed CD4(+) cell count decreases in the Cape Town AIDS Cohort and the Swiss HIV Cohort Study. METHODS: We used mixed-effects models and joint models that allowed for the correlation between CD4(+) cell count decreases and survival and stratified analyses by the initial cell count (50-199, 200-349, 350-499, and 500-750 cells/microL). Results are presented as the mean decrease in CD4(+) cell count with 95% confidence intervals (CIs) during the first year after the initial CD4(+) cell count. RESULTS: A total of 784 South African (629 nonwhite) and 2030 Swiss (218 nonwhite) patients with HIV infection contributed 13,388 CD4(+) cell counts. Decreases in CD4(+) cell count were steeper in white patients, patients with higher initial CD4(+) cell counts, and older patients. Decreases ranged from a mean of 38 cells/microL (95% CI, 24-54 cells/microL) in nonwhite patients from the Swiss HIV Cohort Study 15-39 years of age with an initial CD4(+) cell count of 200-349 cells/microL to a mean of 210 cells/microL (95% CI, 143-268 cells/microL) in white patients in the Cape Town AIDS Cohort > or =40 years of age with an initial CD4(+) cell count of 500-750 cells/microL. CONCLUSIONS: Among both patients from Switzerland and patients from South Africa, CD4(+) cell count decreases were greater in white patients with HIV infection than they were in nonwhite patients with HIV infection.

Proliferation is a prerequisite for bacterial superantigen-induced T cell apoptosis in vivo.

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that binds to major histocompatibility complex class II molecules and selectively interacts with T cells that bear certain T cell receptor (TCR) V beta domains. Administration of SEB in adult mice results in initial proliferation of V beta 8+ T cells followed by a state of unresponsiveness resulting from a combination of clonal deletion and clonal anergy in the SEB-reactive population. At this time, it is unclear what relationship exists between the T cells that have proliferated and those that have been deleted or have become anergic. Here we show that only a fraction of the potentially reactive V beta 8+ T cells proliferate in response to SEB in vivo, and that all the cells that have proliferated eventually undergo apoptosis. Virtually no apoptosis can be detected in the nonproliferating V beta 8+ T cells. These data demonstrate a causal relationship between proliferation and apoptosis in response to SEB in vivo, and they further indicate that T cells bearing the same TCR V beta segment can respond differently to the same superantigen. The implications of this differential responsiveness in terms of activation and tolerance are discussed.