Early neutralizing antibody response against mouse mammary tumor virus: critical role of viral infection and superantigen-reactive T cells.

Infectious mouse mammary tumor virus (MMTV) is a retrovirus that expresses a superantigen shortly after infection of B cells. The superantigen first drives the polyclonal activation and proliferation of superantigen-reactive CD4+ T cells, which then induce the infected B cells to proliferate and differentiate. Part of the MMTV-induced B cell response leads to the production of Abs that are specific for the viral envelope protein gp52. Here we show that this Ab response has virus-neutralizing activity and confers protection against superinfection by other MMTV strains in vivo as soon as 4 to 7 days after infection. A protective Ab titer is maintained lifelong. Viral infection as well as the superantigen-induced T-B collaboration are required to generate this rapid and long lasting neutralizing Ab response. Polyclonal or superantigen-independent B cell activation, on the contrary, does not lead to detectable virus neutralization. The early onset of this superantigen-dependent neutralizing response suggests that viral envelope-specific B cells are selectively recruited to form part of the extrafollicular B cell response and are subsequently amplified and maintained by superantigen-reactive Th cells.

Tumor endothelium FasL establishes a selective immune barrier promoting tolerance in tumors.

We describe a new mechanism regulating the tumor endothelial barrier and T cell infiltration into tumors. We detected selective expression of the death mediator Fas ligand (FasL, also called CD95L) in the vasculature of human and mouse solid tumors but not in normal vasculature. In these tumors, FasL expression was associated with scarce CD8(+) infiltration and a predominance of FoxP3(+) T regulatory (Treg) cells. Tumor-derived vascular endothelial growth factor A (VEGF-A), interleukin 10 (IL-10) and prostaglandin E2 (PGE2) cooperatively induced FasL expression in endothelial cells, which acquired the ability to kill effector CD8(+) T cells but not Treg cells because of higher levels of c-FLIP expression in Treg cells. In mice, genetic or pharmacologic suppression of FasL produced a substantial increase in the influx of tumor-rejecting CD8(+) over FoxP3(+) T cells. Pharmacologic inhibition of VEGF and PGE2 produced a marked increase in the influx of tumor-rejecting CD8(+) over FoxP3(+) T cells that was dependent on attenuation of FasL expression and led to CD8-dependent tumor growth suppression. Thus, tumor paracrine mechanisms establish a tumor endothelial death barrier, which has a critical role in establishing immune tolerance and determining the fate of tumors.

Processing of tumor-associated antigen by the proteasomes of dendritic cells controls in vivo T-cell responses.

Dendritic cells are unique in their capacity to process antigens and prime naive CD8(+) T cells. Contrary to most cells, which express the standard proteasomes, dendritic cells express immunoproteasomes constitutively. The melanoma-associated protein Melan-A(MART1) contains an HLA-A2-restricted peptide that is poorly processed by melanoma cells expressing immunoproteasomes in vitro. Here, we show that the expression of Melan-A in dendritic cells fails to elicit T-cell responses in vitro and in vivo because it is not processed by the proteasomes of dendritic cells. In contrast, dendritic cells lacking immunoproteasomes induce strong anti-Melan-A T-cell responses in vitro and in vivo. These results suggest that the inefficient processing of self-antigens, such as Melan-A, by the immunoproteasomes of professional antigen-presenting cells prevents the induction of antitumor T-cell responses in vivo.

Superantigens of mouse mammary tumor virus.

Superantigens (SAgs) are proteins of microbial origin that bind to major histocompatibility complex (MHC) class II molecules and stimulate T cells via interaction with the V beta domain of the T cell receptor (TCR). Mouse mammary tumor virus (MMTV) is a milk-transmitted type B retrovirus that encodes a SAg in its 3' long terminal repeat. Upon MMTV infection, B cells present SAg to the appropriate T cell subset, which leads to a strong "cognate" T-B interaction. This immune reaction results in preferential clonal expansion of infected B cells and differentiation of some of these cells into long-lived memory cells. In this way a stable MMTV infection is achieved that ultimately results in infection of the mammary gland and virus transmission via milk. Thus, in contrast to many microorganisms that attempt to evade the host immune system (reviewed in 1), MMTV depends upon a strong SAg-induced immune response for its survival. Because of their ability to stimulate very strong T cell responses in MHC-identical mice, minor lymphocyte stimulatory (Mls) antigens, discovered more than 20 years ago, are now known to be SAgs encoded by endogenous MMTV proviruses that have randomly integrated into germ cells. The aim of this review is to combine the extensive biology of Mls SAgs with our current understanding of the life cycle of MMTV.

Percutaneous radiofrequency ablation of primary intraosseous spinal glomus tumor.

The glomus tumor is a rare, benign, but painful vascular neoplasm arising from the neuromyoarterial glomus. Primary intraosseous glomus tumor is even rarer, with only about 20 cases reported in the literature so far, 5 of which involved the spine. Surgical resection is currently considered the treatment of choice. We herewith present an uncommon case of primary intraosseous spinal glomus tumor involving the right pedicle of the eleventh thoracic vertebra (T11). To our knowledge, this is the first case of primary intraosseous spinal glomus tumor successfully treated by percutaneous CT-guided radiofrequency ablation (RFA).

Teichoic acids are not required for Streptococcus pneumoniae and Staphylococcus aureus cell walls to trigger the release of tumor necrosis factor by peripheral blood monocytes.

In gram-negative bacteria, the outer membrane lipopolysaccharide is the main component triggering cytokine release from peripheral blood mononuclear cells (PBMCs). In gram-positive bacteria, purified walls also induce cytokine release, but stimulation requires 100 times more material. Gram-positive walls are complex megamolecules reassembling distinct structures. Only some of them might be inflammatory, whereas others are not. Teichoic acids (TA) are an important portion (> or =50%) of gram-positive walls. TA directly interact with C3b of complement and the cellular receptor for platelet-activating factor. However, their contribution to wall-induced cytokine-release by PBMCs has not been studied in much detail. In contrast, their membrane-bound lipoteichoic acids (LTA) counterparts were shown to trigger inflammation and synergize with peptidoglycan (PGN) for releasing nitric oxide (NO). This raised the question as to whether TA are also inflammatory. We determined the release of tumor necrosis factor (TNF) by PBMCs exposed to a variety of TA-rich and TA-free wall fragments from Streptococcus pneumoniae and Staphylococcus aureus. TA-rich walls from both organisms induced measurable TNF release at concentrations of 1 microg/ml. Removal of wall-attached TA did not alter this activity. Moreover, purified pneumococcal and staphylococcal TA did not trigger TNF release at concentrations as high as > or =100 microg/ml. In contrast, purified LTA triggered TNF release at 1 microg/ml. PGN-stem peptide oligomers lacking TA or amino-sugars were highly active and triggered TNF release at concentrations as low as 0.01 microg/ml (P. A. Majcherczyk, H. Langen, et al., J. Biol. Chem. 274:12537-12543,1999). Thus, although TA is an important part of gram-positive walls, it did not participate to the TNF-releasing activity of PGN.

Intravaginal TLR agonists increase local vaccine-specific CD8 T cells and human papillomavirus-associated genital-tumor regression in mice.

Human papillomaviruses (HPV)-related cervical cancer is the second leading cause of cancer death in women worldwide. Despite active development, HPV E6/E7 oncogene-specific therapeutic vaccines have had limited clinical efficacy to date. Here, we report that intravaginal (IVAG) instillation of CpG-ODN (TLR9 agonist) or poly-(I:C) (TLR3 agonist) after subcutaneous E7 vaccination increased ∼fivefold the number of vaccine-specific interferon-γ-secreting CD8 T cells in the genital mucosa (GM) of mice, without affecting the E7-specific systemic response. The IVAG treatment locally increased both E7-specific and total CD8 T cells, but not CD4 T cells. This previously unreported selective recruitment of CD8 T cells from the periphery by IVAG CpG-ODN or poly-(I:C) was mediated by TLR9 and TLR3/melanoma differentiation-associated gene 5 signaling pathways, respectively. For CpG, this recruitment was associated with a higher proportion of GM-localized CD8 T cells expressing both CCR5 and CXCR3 chemokine receptors and E-selectin ligands. Most interestingly, IVAG CpG-ODN following vaccination led to complete regression of large genital HPV tumors in 75% of mice, instead of 20% with vaccination alone. These findings suggest that mucosal application of immunostimulatory molecules might substantially increase the effectiveness of parenterally administered vaccines.Mucosal Immunology advance online publication 12 September 2012; doi:10.1038/mi.2012.83.

Decreased binding of peptides-MHC class I (pMHC) multimeric complexes to CD8 affects their binding avidity for the TCR but does not significantly impact on pMHC/TCR dissociation rate.

The CD8 coreceptor plays a crucial role in both T cell development in the thymus and in the activation of mature T cells in response to Ag-specific stimulation. In this study we used soluble peptides-MHC class I (pMHC) multimeric complexes bearing mutations in the CD8 binding site that impair their binding to the MHC, together with altered peptide ligands, to assess the impact of CD8 on pMHC binding to the TCR. Our data support a model in which CD8 promotes the binding of TCR to pMHC. However, once the pMHC/TCR complex is formed, the TCR dominates the pMHC/TCR dissociation rates. As a consequence of these molecular interactions, under physiologic conditions CD8 plays a key role in complex formation, resulting in the enhancement of CD8 T cell functions whose specificity, however, is determined by the TCR.

Solid pseudopapillary tumor of the pancreas in children : typical radiological findings and pathological correlation

Introduction : Les tumeurs solides pseudo-papillaires du pancréas (SPT) sont des tumeurs rares, d'étiopathogénie encore incertaine.Le but de notre travail était de décrire les caractéristiques radiologiques des SPT dans le groupe d'âge pédiatrique et d'étudier leur corrélation avec les études anatomopathologiques en vue d'établir un diagnostic.Patients et Méthodes : Nous avons étudié rétrospectivement trois malades pédiatriques pour lesquelles le diagnostic de tumeur solide pseudo-papillaire du pancréas a été porté à l'examen d'une pièce opératoire. Ce groupe comprenait 3 jeunes filles et femmes (âge médian: 13 ans).Résultats : La tumeur a été découverte pendant le bilan de symptômes digestifs non spécifiques. Les examens biologiques n'étaient pas informatifs. Des investigations radiologiques complètes ont été réalisées y compris les ultrasons (US), la tomodensitométrie (CT) et l'imagerie par résonance magnétique (IRM).Celles-ci ont montré de volumineuses lésions nodulaires, peu vascularisées, de compositions habituellement hétérogènes, avec des composantes kystiques et hémorragiques identifiées dans les 3 cas. Un traitement chirurgical a été pratiqué chez toute les patientes. L'étude de la pièce opératoire a montré une tumeur encapsulée dans les 3 cas. Aucune métastase n'a été mise en évidence.Conclusion : Les SPT doivent être considérées dans le diagnostic différentiel des masses pancréatiques pédiatriques, en particulier chez les adolescentes. Certaines caractéristiques radiologiques comme des masses volumineuses bien circonscrites, des lésions hétérogènes avec des zones kystiques et hémorragiques, de plus entourées d'une pseudocapsule fibreuse réactive, suggèrent fortement le diagnostic de SPT. Celui-ci devrait ensuite être confirmé par une biopsie avant que la résection chirurgicale soit effectuée. Chez les enfants, Γ écho graphie abdominale reste la méthode de première intention, suivie par l'IRM comme technique d'imagerie de choix pour évaluer les caractéristiques et l'extension de la lésion, tout en évitant l'exposition des patients aux rayonnements ionisants.

A novel protein family mediates Casparian strip formation in the endodermis.

Polarized epithelia are fundamental to multicellular life. In animal epithelia, conserved junctional complexes establish membrane diffusion barriers, cellular adherence and sealing of the extracellular space. Plant cellular barriers are of independent evolutionary origin. The root endodermis strongly resembles a polarized epithelium and functions in nutrient uptake and stress resistance. Its defining features are the Casparian strips, belts of specialized cell wall material that generate an extracellular diffusion barrier. The mechanisms localizing Casparian strips are unknown. Here we identify and characterize a family of transmembrane proteins of previously unknown function. These 'CASPs' (Casparian strip membrane domain proteins) specifically mark a membrane domain that predicts the formation of Casparian strips. CASP1 displays numerous features required for a constituent of a plant junctional complex: it forms complexes with other CASPs; it becomes immobile upon localization; and it sediments like a large polymer. CASP double mutants display disorganized Casparian strips, demonstrating a role for CASPs in structuring and localizing this cell wall modification. To our knowledge, CASPs are the first molecular factors that are shown to establish a plasma membrane and extracellular diffusion barrier in plants, and represent a novel way of epithelial barrier formation in eukaryotes.

A nonapeptide encoded by human gene MAGE-1 is recognized on HLA-A1 by cytolytic T lymphocytes directed against tumor antigen MZ2-E.

We have reported the identification of human gene MAGE-1, which directs the expression of an antigen recognized on a melanoma by autologous cytolytic T lymphocytes (CTL). We show here that CTL directed against this antigen, which was named MZ2-E, recognize a nonapeptide encoded by the third exon of gene MAGE-1. The CTL also recognize this peptide when it is presented by mouse cells transfected with an HLA-A1 gene, confirming the association of antigen MZ2-E with the HLA-A1 molecule. Other members of the MAGE gene family do not code for the same peptide, suggesting that only MAGE-1 produces the antigen recognized by the anti-MZ2-E CTL. Our results open the possibility of immunizing HLA-A1 patients whose tumor expresses MAGE-1 either with the antigenic peptide or with autologous antigen-presenting cells pulsed with the peptide.