Protection and compensation in the influenza virus-specific CD8+ T cell response.

Influenza virus-specific CD8+ T cells generally recognize peptides derived from conserved, internal proteins that are not subject to antibody-mediated selection pressure. Prior exposure to any one influenza A virus (H1N1) can prime for a secondary CD8+ T cell response to a serologically different influenza A virus (H3N2). The protection afforded by this recall of established CD8+ T cell memory, although limited, is not negligible. Key characteristics of primary and secondary influenza-specific host responses are probed here with recombinant viruses expressing modified nucleoprotein (NP) and acid polymerase (PA) genes. Point mutations were introduced into the epitopes derived from the NP and PA such that they no longer bound the presenting H2Db MHC class I glycoprotein, and reassortant H1N1 and H3N2 viruses were made by reverse genetics. Conventional (C57BL/6J, H2b, and Ig+/+) and Ig-/- (muMT) mice were more susceptible to challenge with the single NP [HKx31 influenza A virus (HK)-NP] and PA (HK-PA) mutants, but unlike the Ig-/- mice, Ig+/+ mice were surprisingly resistant to the HK-NP/-PA double mutant. This virus was found to promote an enhanced IgG response resulting, perhaps, from the delayed elimination of antigen-presenting cells. Antigen persistence also could explain the increase in size of the minor KbPB1703 CD8+ T cell population in mice infected with the mutant viruses. The extent of such compensation was always partial, giving the impression that any virus-specific CD8+ T cell response operates within constrained limits. It seems that the relationship between protective humoral and cellular immunity is neither simple nor readily predicted.

Clustering of Th cell epitopes on exposed regions of HIV envelope despite defects in antibody activity

A long-standing question in the field of immunology concerns the factors that contribute to Th cell epitope immunodominance. For a number of viral membrane proteins, Th cell epitopes are localized to exposed protein surfaces, often overlapping with Ab binding sites. It has therefore been proposed that Abs on B cell surfaces selectively bind and protect exposed protein fragments during Ag processing, and that this interaction helps to shape the Th cell repertoire. While attractive in concept, this hypothesis has not been thoroughly tested. To test this hypothesis, we have compared Th cell peptide immunodominance in normal C57BL/6 mice with that in C57BL/6MT/MT mice (lacking normal B cell activity). Animals were first vaccinated with DNA constructs expressing one of three different HIV envelope proteins, after which the CD4 T cell response profiles were characterized toward overlapping peptides using an IFN- ELISPOT assay. We found a striking similarity between the peptide response profiles in the two mouse strains. Profiles also matched those of previous experiments in which different envelope vaccination regimens were used. Our results clearly demonstrate that normal Ab activity is not required for the establishment or maintenance of Th peptide immunodominance in the HIV envelope response. To explain the clustering of Th cell epitopes, we propose that localization of peptide on exposed envelope surfaces facilitates proteolytic activity and preferential peptide shuttling through the Ag processing pathway.

Influenza A virus-specific CD8.sup.+ T-cell responses : from induction to function

Seasonal influenza virus infection is a leading cause of illness and mortality in young children and the elderly each year. Current influenza vaccines generate protective antibody responses; however, these must be given annually to provide protection against serologically distinct viruses. By contrast, CD8.sup.+ T cells are capable of recognizing conserved antigenic determinants within the influenza virion and, as such, may provide protection against a number of variant strains of the virus. CD8.sup.+ T cells play a critical key role in controlling and resolving influenza virus infections via the production of cytokines and cytolytic mediators. This article focuses on the induction of the influenza-specific CD8.sup.+ T-cell response and how these cells acquire and maintain effector function after induction. Moreover, we discuss how cytotoxic T-lymphocyte function correlates with protection following vaccination.

Medial prefrontal cortex control of the paraventricular hypothalamic nucleus response to psychological stress : possible role of the bed nucleus of the stria terminalis

The medial prefrontal cortex (mPFC) has been strongly implicated in control of the paraventricular nucleus of the hypothalamus (PVN) response to stress. Because of the paucity of direct projections from the mPFC to the PVN, we sought to investigate possible brain regions that might act as a relay between the two during psychological stress. Bilateral ibotenic acid lesions of the rat mPFC enhanced the number of Fos-immunoreactive cells seen in the PVN after exposure to the psychological stressor, air puff. Altered neuronal recruitment was seen in only one of the candidate relay populations examined, the ventral bed nucleus of the stria terminalis (vBNST). Furthermore, bilateral ibotenic acid lesions of the BNST caused a significant attenuation of the PVN response to air puff. To better characterize the structural relationships between the mPFC and PVN, retrograde tracing studies were conducted examining Fos expression in cells retrogradely labeled with cholera toxin b subunit (CTb) from the PVN and the BNST. Results obtained were consistent with an important role for both the mPFC and BNST in the mpPVN CRF cell response to air puff. We suggest a set of connections whereby a direct PVN projection from the ipsilateral vBNST is involved in the mpPVN response to air puff and this may, in turn, be modulated by an indirect projection from the mPFC to the BNST.

Influenza A virus infection impairs mycobacteria-specific T cell responses and mycobacterial clearance in the lung during pulmonary coinfection.

Individuals infected with mycobacteria are likely to experience episodes of concurrent infections with unrelated respiratory pathogens, including the seasonal or pandemic circulating influenza A virus strains. We analyzed the impact of influenza A virus and mycobacterial respiratory coinfection on the development of CD8 T cell responses to each pathogen. Coinfected mice exhibited reduced frequency and numbers of CD8 T cells specific to Mycobacterium bovis bacille Calmette-Guérin (BCG) in the lungs, and the IFN-γ CD8 T cell response to BCG-encoded OVA was decreased in the lungs of coinfected mice, when compared with mice infected with BCG alone. Moreover, after 2 wk of infection, mice coinfected with both pathogens showed a significant increase in the number of mycobacteria present in the lung compared with mice infected with BCG only. Following adoptive transfer into coinfected mice, transgenic CD8 T cells specific for OVA257–264 failed to proliferate as extensively in the mediastinal lymph nodes as in mice infected only with BCG-OVA. Also noted was a reduction in the proliferation of BCG-specific CD4 transgenic T cells in mice coinfected with influenza compared with mice infected with BCG alone. Furthermore, phenotypic analysis of CD11c+ dendritic cells from mediastinal lymph nodes of the infected mice showed that coinfection was associated with decreased surface expression of MHC class II and class I. Thus, concurrent pulmonary infection with influenza A virus is associated with decreased MHC expression on dendritic cells, reduced activation of BCG-specific CD4 and CD8 T cells, and impaired clearance of mycobacteria.

The influence of titania-zirconia-zirconium titanate nanotube characteristics on osteoblast cell adhesion

Studies of biomaterial surfaces and their influence on cell behavior provide insights concerning the design of surface physicochemical and topography properties of implant materials. Fabrication of biocompatible metal oxide nanotubes on metallic biomaterials, especially titanium alloys such as Ti50Zr via anodization, alters the surface chemistry as well as surface topography of the alloy. In this study, four groups of TiO2-ZrO2-ZrTiO4 nanotubes that exhibit diverse nanoscale dimensional characteristics (i.e. inner diameter Di, outer diameter Do and wall thicknesses Wt) were fabricated via anodization. The nanotubes were annealed and characterized using scanning electron microscopy and 3-D profilometry. The potential applied during anodization influenced the oxidation rate of titanium and zirconium, thereby resulting in different nanoscale characteristics for the nanotubes. The different oxidation and dissolution rates both led to changes in the surface roughness parameters. The in vitro cell response to the nanotubes with different nanoscale dimensional characteristics was assessed using osteoblast cells (SaOS2). The results of the MTS assay indicated that the nanotubes with inner diameter (Di)≈40nm exhibited the highest percentage of cell adhesion of 41.0%. This result can be compared to (i) 25.9% cell adhesion at Di≈59nm, (ii) 33.1% at Di≈64nm, and (iii) 33.5% at Di≈82nm. The nanotubes with Di≈59nm exhibited the greatest roughness parameter of Sa (mean roughness), leading to the lowest ability to interlock with SaOS2 cells.

Differential tumor necrosis factor receptor 2-mediated editing of virus-specific CD8+ effector T cells

Much of the CD8+ T cell response in H2b mice with influenza pneumonia is directed at the nucleoprotein366-374 (NP366) and acid polymerase224-233 (PA224) peptides presented by the H2Db MHC class I glycoprotein. These DbNP366- and DbPA224-specific T cell populations are readily analyzed by staining with tetrameric complexes of MHC+ peptide (tetramers) or by cytokine production subsequent to in vitro stimulation with the cognate peptides. The DbPA224-specific CD8+ effector T cells make more tumor necrosis factor (TNF) α than the comparable CD8+DbNP366+ set, a difference reflected in the greater sensitivity of the CD8+DbPA224+ population to TNF receptor (TNFR) 2-mediated apoptosis under conditions of in vitro culture. Freshly isolated CD8+DbNP366+ and CD8+DbPA224+ T cells from influenza-infected TNFR2-/- mice produce higher levels of IFN-γ and TNF-α after in vitro stimulation with peptide, although the avidity of the T cell receptor-epitope interaction does not change. Increased numbers of both CD8+DbPA224+ and CD8+DbNP366+ T cells were recovered from the lungs (but not the spleens) of secondarily challenged TNFR2-/- mice, a pattern that correlates with the profiles of TNFR expression in the TNFR2+/+ controls. Thus, it seems that TNFR2-mediated editing of influenza-specific CD8+ T cells functions to limit the numbers of effectors that have localized to the site of pathology in the lung but does not modify the size of the less activated responder T cell populations in the spleen. Therefore, the massive difference in magnitude for the secondary, although not the primary, response to these DbNP366 and DbPA224 epitopes cannot be considered to reflect differential TNFR2-mediated T cell editing.

Toll like receptors play a role in general immunity, eye infection and inflammation : TLRs for nanodelivery

Dendritic cells [DCs] are potent antigen presenting cells [APC], which plays a vital role in immune system by detecting and capturing pathogens in the body. DCs perform a pivotal role in induction of T cell response. Regulation of immune response can be achieved by specific antigen [Ag] delivery to DCs. A delivery system that can efficiently target and present Ags to DCs for the purpose of anti-tumour activity is currently a topic of significant research interest. DCs are receiving attention due to their key role in anti cancer host response and due to their adjuvanic property in tumour vaccines. Role of toll like receptors [TLR] in innate immune system and their part in eventual stimulation of adaptive immunity is exploited to develop vaccines. TLR agonists in conjugation with vaccines are shown to increase therapeutic efficacy in some cases. TLRs also play a vital role in protecting the cornea from invading pathogens. Due to adverse effects in the treatment of ocular inflammations, cancer and in viral infections, an alternate approach such as the use of TLRs will solve the inquisitive question regarding side effects. The intended delivery is attained by the use of nanoparticles which in turn leads to prolonged half-life in the body. Co-delivery of Ags, TLRs and immunomodulators using nanoparticles has been demonstrated to elicit potent cellular immune responses and are currently under development of clinically applicable immunisations and vaccines.

The central nucleus of the amygdala ; a conduit for modulation of HPA axis responses to an immune challenge?

Physical stressors such as infection, inflammation and tissue injury elicit activation of the hypofhalamic-pituitary-adrenal (HPA) axis. This response has significant implications for both immune and central nervous system function. Investigations in rats into the neural substrates responsible for HPA axis activation to an immune challenge have predominantly utilized an experimental paradigm involving the acute administration of the pro-inflammatory cytokine interleukin-1 β (IL-1β). It is well recognized that medial parvocellular corticotrophin-releasing factor cells of the paraventricular nucleus (mPVN CRF) are critical in generating HPA axis responses to an immune challenge but little is known about how peripheral immune signals can activate and/or modulate the mPVN CRF cells. Studies that have examined the afferent control of the mPVN CRF cell response to systemic IL-1β have centred largely on the inputs from brainstem catecholamine cells. However, other regulatory neuronal populations also merit attention and one such region is a component of the limbic system, the central nucleus of the amygdala (CeA). A large number of CeA cells are recruited following systemic IL-lβ administration and there is a significant body of work indicating that the CeA can influence HPA axis function. However, the contribution of the CeA to HPA axis responses to an immune challenge is only just beginning to be addressed. This review examines three aspects of HPA axis control by systemic IL-lβ; (i) whether the CeA has a role in generating HPA axis responses to systemic IL-1 β, (ii) the identity of the neural connections between the CeA and mPVN CRF cells that might be important to HPA axis responses and (iii) the mechanisms by which systemic IL-lβ triggers the recruitment of CeA cells.

Ti-SrO metal matrix composites for bone implant materials

Titanium-strontia (Ti-SrO) metal matrix composites (MMCs) with 0, 1, 3 and 5% (weight ratio) of SrO have been fabricated through the powder metallurgy method. Increasing the weight ratio of SrO from 0 to 5%, the compressive strength of Ti-SrO MMCs increased from 982 MPa to 1753 MPa, while the ultimate strain decreased from 0.28 to 0.05. The elastic moduli of Ti-3SrO and Ti-5SrO MMCs were higher than those of Ti and Ti-1SrO MMC samples. Additionally, the micro hardness of Ti-SrO MMCs was enhanced from 59% to 190% with the addition of SrO. The enhanced compression strength and micro hardness of Ti-SrO MMCs were attributed to the Hall-Petch effect and the SrO dispersion strengthening in the Ti matrix. MTS assay results demonstrated that Ti-SrO MMCs with 3% SrO exhibited enhanced proliferation of osteoblast-like cells. Alkaline phosphatase activity of cells was not influenced significantly on the surface of Ti-SrO MMCs compared with pure Ti in a term longer than 10 days. The cell morphology on the Ti-SrO MMCs was observed using confocal microscopy and scanning electron microscopy, which confirmed that the Ti-3%SrO MMCs showed optimal in vitro biocompatibility. This journal is © the Partner Organisations 2014.

Processing and characterization of srTiO₃-TiO₂ nanoparticle-nanotube heterostructures on titanium for biomedical applications

Surface properties such as physicochemical characteristics and topographical parameters of biomaterials, essentially determining the interaction between the biological cells and the biomaterial, are important considerations in the design of implant materials. In this study, a layer of SrTiO3-TiO2 nanoparticle-nanotube heterostructures on titanium has been fabricated via anodization combined with a hydrothermal process. Titanium was anodized to create a layer of titania (TiO2) nanotubes (TNTs), which was then decorated with a layer of SrTiO3 nanoparticles via hydrothermal processing. SrTiO3-TiO2 heterostructures with high and low volume fraction of SrTiO3 nanoparticle (denoted by 6.3-Sr/TNTs and 1.4-Sr/TNTs) were achieved by using a hydrothermal processing time of 12 and 3 h, respectively. The in vitro biocompatibility of the SrTiO3-TiO2 heterostructures was assessed by using osteoblast cells (SaOS2). Our results indicated that the SrTiO3-TiO2 heterostructures with different volume fractions of SrTiO3 nanoparticles exhibited different Sr ion release in cell culture media and different surface energies. An appropriate volume fraction of SrTiO3 in the heterostructures stimulated the secretion of cell filopodia, leading to enhanced biocompatibility in terms of cell attachment, anchoring, and proliferation on the heterostructure surface.