CD8(+) T cell-mediated injury in vivo progresses in the absence of effector T cells

Perforin and Fas cytolytic pathways coordinately shape the selection and diversity of CD8+-T-cell escape variants of influenza virus

Antigenic variation is a viral strategy exploited to promote survival in the face of the host immune response and represents a major challenge for efficient vaccine development. Influenza viruses are pathogens with high transmissibility and mutation rates, enabling viral escape from immunity induced by prior infection or vaccination. Intense selection from neutralizing antibody drives antigenic changes in the surface glycoproteins, resulting in emergence of new strains able to reinfect hosts immune to previously circulating viruses. CD8+ cytotoxic T cells (CTLs) also provide protective immunity from influenza virus infection and may contribute to the antigenic evolution of influenza viruses. Utilizing mice transgenic for an influenza virus NP366-374 peptide-specific T-cell receptor, we demonstrated that the respiratory tract is a suitable site for generation of escape variants of influenza virus selected by CTL in vivo. In this report the contributions of the perforin and Fas pathways utilized by influenza virus-specific CTLs in viral clearance and selection of CTL escape variants have been evaluated. While transgenic CTLs deficient in either perforin- or Fas-mediated pathways are efficient in initial pulmonary viral control, variant virus emergence was observed in all the mice studied, although the spectrum of viral CTL escape variants selected varied profoundly. Thus, a less-restricted repertoire of escape variants was observed in mice with an intact perforin cytotoxic pathway compared with a limited variant diversity in perforin pathway-deficient mice, although maximal variant diversity was observed in mice having both Fas and perforin pathways intact. We conclude that selection of viral CTL escape variants reflects coordinate action between the tightly controlled perforin/granzyme pathway and the more promiscuous Fas/FasL pathway.

CD8+ T lymphocytes in lung tissue from patients with idiopathic pulmonary fibrosis

Background

Several studies have implicated a role of inflammation in the pathogenesis of lung damage in idiopathic pulmonary fibrosis (IPF). Parenchymal lung damage leads to defects in mechanics and gas exchange and clinically manifests with exertional dyspnea. Investigations of inflammatory cells in IPF have shown that eosinophils, neutrophils and CD₈₊ TLs may be associated with worse prognosis. We wished to investigate by quantitative immunohistochemistry infiltrating macrophages, neutrophils and T lymphocytes (TLs) subpopulations (CD₃₊, CD₄₊ and CD₈₊) in lung tissue of patients with IPF and their correlation with lung function indices and grade of dyspnoea.

Methods

Surgical biopsies of 12 patients with IPF were immunohistochemically stained with mouse monoclonal antibodies (anti-CD₆₈ for macrophages, anti-elastase for neutrophils, and anti-CD₃, anti-CD₄, anti-CD₈ for CD₃₊TLs, CD₄₊TLs, and CD₈₊TLs respectively). The number of positively stained cells was determined by observer-interactive computerized image analysis (SAMBA microscopic image processor). Cell numbers were expressed in percentage of immunopositive nuclear surface in relation to the total nuclear surface of infiltrative cells within the tissue (labeling Index). Correlations were performed between cell numbers and physiological indices [FEV₁, FVC, TLC, DLCO, PaO₂, PaCO₂ and P(A-a)O₂)] as well as dyspnoea scores assessed by the Medical Research Council (MRC) scale.

Results

Elastase positive cells accounted for the 7.04% ± 1.1 of total cells, CD₆₈₊ cells for the 16.6% ± 2, CD₃₊ TLs for the 28.8% ± 7, CD₄₊ TLs for the 14.5 ± 4 and CD₈₊ TLs for the 13.8 ± 4. CD₈₊TLs correlated inversely with FVC % predicted (r_s = -0.67, p = 0.01), TLC % predicted (r_s = -0.68, p = 0.01), DLCO % predicted (r_s = -0.61, p = 0.04), and PaO₂ (r_s = -0.60, p = 0.04). Positive correlations were found between CD₈₊TLs and P(A-a)O₂ (r_s = 0.65, p = 0.02) and CD₈₊TLs and MRC score (r_s = 0.63, p = 0.02). Additionally, CD₆₈₊ cells presented negative correlations with both FVC % predicted (r_s = -0.80, p = 0.002) and FEV₁ % predicted (r_s = -0.68, p = 0.01).

Conclusion

In UIP/IPF tissue infiltrating mononuclear cells and especially CD₈₊ TLs are associated with the grade of dyspnoea and functional parameters of disease severity implicating that they might play a role in its pathogenesis.

No apoptotic deaths and different levels of inductions of inflammatory cytokines in alveolar macrophages infected with influenza viruses

Influenza viruses are reported to infect mainly the respiratory tract epithelium of hosts. Our studies in a pig model show that influenza A viruses infect alveolar macrophages that constitutively reside in the respiratory tract, without causing apoptosis. Tumor necrosis factor alpha was the inflammatory cytokine most highly induced in these macrophages. In vivo, alveolar macrophages infected with human H3N2 influenza virus showed greater expression of tumor necrosis factor alpha than did alveolar macrophages infected with human H1N1 influenza virus. Induction of specific inflammatory cytokine such as TNF-alpha is a polygenic trait that involves the HA and NA genes. Markedly elevated expression of tumor necrosis factor alpha may be responsible for the high mortality rate caused by H3N2 influenza virus infection in elderly patients.

Manipulation of immunity to and pathology of respiratory infections

Respiratory infections are the third leading cause of death worldwide and are a priority for vaccine development. Immune defence mechanisms are critical in recovery from most respiratory infections but the role of the immune system in causing bystander lung injury is not as well understood, and will be the focus of this review. Immune-mediated injury results from physical occlusion of the airways or the ensuing 'cytokine storm', which may spill over into the systemic circulation and cause devastating consequences. Respiratory pathogens employ numerous strategies to avoid detection by the immune system. One of these, the alteration of key surface determinants, makes the design of rational vaccines problematic. In the following review the immune compartments responsible for clinical lung disease are discussed, and current and novel strategies to reduce their potency are overviewed.

Cutting edge: pulmonary immunopathology mediated by antigen-specific expression of TNF-alpha by antiviral CD8+ T cells

Respiratory virus infection results in considerable pulmonary immunopathology, a component of which results from the host immune responses. We have developed a murine model to specifically examine the lung injury due to CD8(+) T cell recognition of an influenza hemagglutinin (HA) transgene on lung epithelium in the absence of replicating virus, after adoptive transfer. Lung injury is largely mediated by chemokines expressed by the epithelial cells upon T cell recognition mediated by TNF-alpha. To determine the critical source of TNF-alpha, HA-specific TNF(-/-) CD8(+) T cells were transferred into HA transgenic animals, and lung injury was not observed, though these T cells exhibited no defect in antiviral activity in vivo. This indicates that the initiating event in the injury process is Ag-specific expression of TNF-alpha by antiviral CD8(+) T cells upon recognition of alveolar epithelial Ag, and that the effector activities responsible for viral clearance may be dissociable from those resulting in immunopathology.

TNF Receptor Signaling Contributes to Chemokine Secretion, Inflammation, and Respiratory Deficits duringPneumocystisPneumonia

CD8(+) T cells contribute to the pathophysiology of Pneumocystis pneumonia (PcP) in a murine model of AIDS-related disease. The present studies were undertaken to more precisely define the mechanisms by which these immune cells mediate the inflammatory response that leads to lung injury. Experimental mice were depleted of either CD4(+) T cells or both CD4(+) and CD8(+) T cells and then infected with Pneumocystis: The CD4(+)-depleted mice had significantly greater pulmonary TNF-alpha levels than mice depleted of both CD4(+) and CD8(+) T cells. Elevated TNF-alpha levels were associated with increased lung concentrations of the chemokines RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant. To determine whether TNFR signaling was involved in the CD8(+) T cell-dependent chemokine response, TNFRI- and II-deficient mice were CD4(+) depleted and infected with Pneumocystis: TNFR-deficient mice had significantly reduced pulmonary RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant responses, reduced inflammatory cell recruitment to the alveoli, and reduced histological evidence of PcP-related alveolitis as compared with infected wild-type mice. Diminished pulmonary inflammation correlated with improved surfactant activity and improved pulmonary function in the TNFR-deficient mice. These data indicate that TNFR signaling is required for maximal CD8(+) T cell-dependent pulmonary inflammation and lung injury during PcP and also demonstrate that CD8(+) T cells can use TNFR signaling pathways to respond to an extracellular fungal pathogen.

Virokinin, a bioactive peptide of the tachykinin family, is released from the fusion protein of bovine respiratory syncytial virus

Tachykinins, an evolutionary conserved family of peptide hormones in both invertebrates and vertebrates, are produced by neuronal cells as inactive preprotachykinins that are post-translationally processed into different neuropeptides such as substance P, neurokinin A, and neurokinin B. We show here that furin-mediated cleavage of the bovine respiratory syncytial virus fusion protein results in the release of a peptide that is converted into a biologically active tachykinin (virokinin) by additional post-translational modifications. An antibody directed to substance P cross-reacted with the C terminus of mature virokinin that contains a classical tachykinin motif. The cellular enzymes involved in the C-terminal maturation of virokinin were found to be present in many established cell lines. Virokinin is secreted by virus-infected cells and was found to act on the tachykinin receptor 1 (TACR1), leading to rapid desensitization of this G protein-coupled receptor as shown by TACR1-green fluorescent protein conjugate translocation from the cell surface to endosomes and by co-internalization of the receptor with beta-arrestin 1-green fluorescent protein conjugates. In vitro experiments with isolated circular muscle from guinea pig stomach indicated that virokinin is capable of inducing smooth muscle contraction by acting on the tachykinin receptor 3. Tachykinins and their cognate receptors are present in the mammalian respiratory tract, where they have potent effects on local inflammatory and immune processes. The viral tachykinin-like peptide represents a novel form of molecular mimicry, which may benefit the virus by affecting the host immune response.

Absence of the macrophage mannose receptor in mice does not increase susceptibility to Pneumocystis carinii infection in vivo

Host defense against the opportunistic pathogen Pneumocystis carinii requires functional interactions of many cell types. Alveolar macrophages are presumed to be a vital host cell in the clearance of P. carinii, and the mechanisms of this interaction have come under scrutiny. The macrophage mannose receptor is believed to play an important role as a receptor involved in the binding and phagocytosis of P. carinii. Although there is in vitro evidence for this interaction, the in vivo role of this receptor in P. carinii clearance in unclear. Using a mouse model in which the mannose receptor has been deleted, we found that the absence of this receptor is not sufficient to allow infection by P. carinii in otherwise immunocompetent mice. Furthermore, when mice were rendered susceptible to P. carinii by CD4(+) depletion, mannose receptor knockout mice (MR-KO) had pathogen loads equal to those of wild-type mice. However, the MR-KO mice exhibited a greater influx of phagocytes into the alveoli during infection. This was accompanied by increased pulmonary pathology in the MR-KO mice, as well as greater accumulation of glycoproteins in the alveoli (glycoproteins, including harmful hydrolytic enzymes, are normally cleared by the mannose receptor). We also found that the surface expression of the mannose receptor is not downregulated during P. carinii infection in wild-type mice. Our findings suggest that while the macrophage mannose receptor may be important in the recognition of P. carinii, in vivo, this mechanism may be redundant, and the absence of this receptor may be compensated for.

A critical role for CCR2/MCP-1 interactions in the development of idiopathic pneumonia syndrome after allogeneic bone marrow transplantation

Idiopathic pneumonia syndrome (IPS) is a major complication after allogeneic bone marrow transplantation (allo-BMT) and involves the infiltration of donor leukocytes and the secretion of inflammatory cytokines. We hypothesized that leukocyte recruitment during IPS is dependent in part upon interactions between chemokine receptor 2 (CCR2) and its primary ligand monocyte chemoattractant protein-1 (MCP-1). To test this hypothesis, IPS was induced in a lethally irradiated parent --> F1 mouse BMT model. Compared with syngeneic controls, pulmonary expression of MCP-1 and CCR2 mRNA was significantly increased after allo-BMT. Transplantation of CCR2-deficient (CCR2-/-) donor cells resulted in a significant reduction in IPS severity compared with transplantation of wild-type (CCR2+/+) cells and in reduced bronchoalveolar lavage (BAL) fluid cellularity and BAL fluid levels of tumor necrosis factor-alpha (TNF-alpha) and soluble p55 TNF receptor (sTNFRI). In addition, neutralization of MCP-1 resulted in significantly decreased lung injury compared with control-treated allogeneic recipients. Experimental data correlated with preliminary clinical findings; patients with IPS have elevated levels of MCP-1 in the BAL fluid at the time of diagnosis. Collectively, these data demonstrate that CCR2/MCP-1 interactions significantly contribute to the development of experimental IPS and suggest that interventions blocking these receptor-ligand interactions may represent novel strategies to prevent or treat this lethal complication after allo-BMT.

Cell-mediated immunity to respiratory virus infections

The mucosal surfaces of the lungs pose tremendous problems for an immune system charged with maintaining a sterile pulmonary environment. Despite these problems, the immune system is effective at controlling most pulmonary infections. Over the past few years significant progress has been made in our understanding of how adaptive (humoral and cellular) immunity is able to control infections in the respiratory tract. Recent advances include the identification of effector memory T-cell populations in the lungs and an appreciation for the role of cytokines in regulating memory T-cell pools.

LFA-1 is required for retention of effector CD8 T cells in mouse lungs

The adhesion molecules involved in the migration and retention of activated effector CD8 T cells in the lung microcirculation and their recruitment into lung tissue are largely unknown. Here, we have analyzed the role of lymphocyte function-associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4) on adhesion of influenza hemagglutinin (HA)-specific CD8 T-cell clone D4 under shear conditions in an in vitro binding assay and in an in vivo homing assay to the lungs of naive or transgenic Balb/c mice expressing HA (HA-Tg) by a lung-specific promoter. Blocking LFA-1 or intercellular adhesion molecule 1 (ICAM-1) significantly inhibited adhesion of D4 cells to lung vascular endothelium and parenchyma of lung sections. However, blocking VLA-4 or vascular cell adhesion molecule 1 (VCAM-1) had no effect on cell adhesion. Blocking LFA-1 in vivo significantly delayed lethal injury following adoptive transfer of D4 cells into HA-Tg mice as assessed by weight loss and histology. Residence time of adoptively transferred Indium 111 (111In)-labeled D4 cells in lungs of normal and HA-Tg mice as analyzed by dual modality imaging revealed a significantly shorter transit time of 4 hours for the D4 cells upon in vivo blockade of LFA-1. These results demonstrate a crucial role for LFA-1 in retention of activated CD8 T cells in normal mouse lungs and in the progression of lethal injury in HA-Tg mice.