Regulation of T-cell activation in the lung: isolated lung T cells exhibit surface phenotypic characteristics of recent activation including down-modulated T-cell receptors, but are locked into the G0/G1 phase of the cell cycle

Shaping of the alveolar landscape by respiratory infections and long-term consequences for lung immunity

Respiratory infections and especially viral infections, along with other extrinsic environmental factors, have been shown to profoundly affect macrophage populations in the lung. In particular, alveolar macrophages (AMs) are important sentinels during respiratory infections and their disappearance opens a niche for recruited monocytes (MOs) to differentiate into resident macrophages. Although this topic is still the focus of intense debate, the phenotype and function of AMs that recolonize the niche after an inflammatory insult, such as an infection, appear to be dictated in part by their origin, but also by local and/or systemic changes that may be imprinted at the epigenetic level. Phenotypic alterations following respiratory infections have the potential to shape lung immunity for the long-term, leading to beneficial responses such as protection against allergic airway inflammation or against other infections, but also to detrimental responses when associated with the development of immunopathologies. This review reports the persistence of virus-induced functional alterations in lung macrophages, and discusses the importance of this imprinting in explaining inter-individual and lifetime immune variation.

Multiple Death Pathways of Neutrophils Regulate Alveolar Macrophage Proliferation

Alveolar macrophage (AM) proliferation and self-renewal play an important role in the lung tissue microenvironment. However, the impact of immune cells, especially the neutrophils, on AM homeostasis or function is not well characterized. In this study, we induced in vivo migration of neutrophils into bronchoalveolar lavage (BAL) fluid and lung using CXCL1, and then co-cultured these with AMs in vitro. Neutrophils in the BAL (BAL-neutrophils), rather than neutrophils of bone marrow (BM-neutrophils), were found to inhibit AM proliferation. Analysis of publicly available data showed high heterogeneity of lung neutrophils with distinct molecular signatures of BM- and blood-neutrophils. Unexpectedly, BAL-neutrophils from influenza virus PR8-infected mice (PR8-neutrophils) did not inhibit the proliferation of AMs. Bulk RNA sequencing further revealed that co-culture of AMs with PR8-neutrophils induced IFN-α and -γ responses and inflammatory response, and AMs co-cultured with BAL-neutrophils showed higher expression of metabolism- and ROS-associated genes; in addition, BAL-neutrophils from PR8-infected mice modulated AM polarization and phagocytosis. BAL-neutrophil-mediated suppression of AM proliferation was abrogated by a combination of inhibitors of different neutrophil death pathways. Collectively, our findings suggest that multiple cell death pathways of neutrophils regulate the proliferation of AMs. Targeting neutrophil death may represent a potential therapeutic strategy for improving AM homeostasis during respiratory diseases.

Critical Role of Lkb1 in the Maintenance of Alveolar Macrophage Self-Renewal and Immune Homeostasis

Alveolar macrophages (AMs) are pivotal for maintaining lung immune homeostasis. We demonstrated that deletion of liver kinase b1 (Lkb1) in CD11c+ cells led to greatly reduced AM abundance in the lung due to the impaired self-renewal of AMs but not the impeded pre-AM differentiation. Mice with Lkb1-deficient AMs exhibited deteriorated diseases during airway Staphylococcus aureus (S. aureus) infection and allergic inflammation, with excessive accumulation of neutrophils and more severe lung pathology. Drug-mediated AM depletion experiments in wild type mice indicated a cause for AM reduction in aggravated diseases in Lkb1 conditional knockout mice. Transcriptomic sequencing also revealed that Lkb1 inhibited proinflammatory pathways, including IL-17 signaling and neutrophil migration, which might also contribute to the protective function of Lkb1 in AMs. We thus identified Lkb1 as a pivotal regulator that maintains the self-renewal and immune function of AMs.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.

What lies beneath the airway mucosal barrier? Throwing the spotlight on antigen-presenting cell function in the lower respiratory tract

The global prevalence of respiratory infectious and inflammatory diseases remains a major public health concern. Prevention and management strategies have not kept pace with the increasing incidence of these diseases. The airway mucosa is the most common portal of entry for infectious and inflammatory agents. Therefore, significant benefits would be derived from a detailed understanding of how immune responses regulate the filigree of the airways. Here, the role of different antigen‐presenting cells (APC) in the lower airways and the mechanisms used by pathogens to modulate APC function during infectious disease is reviewed. Features of APC that are unique to the airways and the influence they have on uptake and presentation of antigen to T cells directly in the airways are discussed. Current information on the crucial role that airway APC play in regulating respiratory infection is summarised. We examine the clinical implications of APC dysregulation in the airways on asthma and tuberculosis, two chronic diseases that are the major cause of illness and death in the developed and developing world. A brief overview of emerging therapies that specifically target APC function in the airways is provided.

Tissue-resident innate immunity in the lung

The lung is a unique organ that must protect against inhaled pathogens and toxins, without mounting a disproportionate response against harmless particulate matter and without compromising its vital function. Tissue-resident immune cells within the lung provide local immunity and protection from infection but are also responsible for causing disease when dysregulated. There is a growing appreciation of the importance of tissue-resident memory T cells to lung immunity, but non-recirculating, tissue-resident, innate immune cells also exist. These cells provide the first line of defence against pulmonary infection and are essential for co-ordinating the subsequent adaptive response. In this review, we discuss the main lung-resident innate immune subsets and their functions in common pulmonary diseases, such as influenza, bacterial pneumonia, asthma and inflammatory disorders.

Identification and characterization of a novel anti-inflammatory lipid isolated from Mycobacterium vaccae, a soil-derived bacterium with immunoregulatory and stress resilience properties

RATIONALE

Mycobacterium vaccae (NCTC 11659) is an environmental saprophytic bacterium with anti-inflammatory, immunoregulatory, and stress resilience properties. Previous studies have shown that whole, heat-killed preparations of M. vaccae prevent allergic airway inflammation in a murine model of allergic asthma. Recent studies also demonstrate that immunization with M. vaccae prevents stress-induced exaggeration of proinflammatory cytokine secretion from mesenteric lymph node cells stimulated ex vivo, prevents stress-induced exaggeration of chemically induced colitis in a model of inflammatory bowel disease, and prevents stress-induced anxiety-like defensive behavioral responses. Furthermore, immunization with M. vaccae induces anti-inflammatory responses in the brain and prevents stress-induced exaggeration of microglial priming. However, the molecular mechanisms underlying anti-inflammatory effects of M. vaccae are not known.

OBJECTIVES

Our objective was to identify and characterize novel anti-inflammatory molecules from M. vaccae NCTC 11659.

METHODS

We have purified and identified a unique anti-inflammatory triglyceride, 1,2,3-tri [Z-10-hexadecenoyl] glycerol, from M. vaccae and evaluated its effects in freshly isolated murine peritoneal macrophages.

RESULTS

The free fatty acid form of 1,2,3-tri [Z-10-hexadecenoyl] glycerol, 10(Z)-hexadecenoic acid, decreased lipopolysaccharide-stimulated secretion of the proinflammatory cytokine IL-6 ex vivo. Meanwhile, next-generation RNA sequencing revealed that pretreatment with 10(Z)-hexadecenoic acid upregulated genes associated with peroxisome proliferator-activated receptor alpha (PPARα) signaling in lipopolysaccharide-stimulated macrophages, in association with a broad transcriptional repression of inflammatory markers. We confirmed using luciferase-based transfection assays that 10(Z)-hexadecenoic acid activated PPARα signaling, but not PPARγ, PPARδ, or retinoic acid receptor (RAR) α signaling. The effects of 10(Z)-hexadecenoic acid on lipopolysaccharide-stimulated secretion of IL-6 were prevented by PPARα antagonists and absent in PPARα-deficient mice.

CONCLUSION

Future studies should evaluate the effects of 10(Z)-hexadecenoic acid on stress-induced exaggeration of peripheral inflammatory signaling, central neuroinflammatory signaling, and anxiety- and fear-related defensive behavioral responses.

The development and function of lung-resident macrophages and dendritic cells

Gas exchange is the vital function of the lungs. It occurs in the alveoli, where oxygen and carbon dioxide diffuse across the alveolar epithelium and the capillary endothelium surrounding the alveoli, separated only by a fused basement membrane 0.2-0.5 μm in thickness. This tenuous barrier is exposed to dangerous or innocuous particles, toxins, allergens and infectious agents inhaled with the air or carried in the blood. The lung immune system has evolved to ward off pathogens and restrain inflammation-mediated damage to maintain gas exchange. Lung-resident macrophages and dendritic cells are located in close proximity to the epithelial surface of the respiratory system and the capillaries to sample and examine the air-borne and blood-borne material. In communication with alveolar epithelial cells, they set the threshold and the quality of the immune response.

Alveolar macrophages contribute to respiratory tolerance by inducing FoxP3 expression in naive T cells

Alveolar macrophages (AMs) from mice and humans have long been known to contribute to maintaining tolerance in the lung. Studies have shown that AMs can induce anergy in CD4(+) T cells. Nitric oxide, prostaglandins, and leukotrienes have been implicated in AM-mediated tolerance. However, it remains unclear what effect, if any, AMs exert on FoxP3 induction in CD4(+) T cells from mice and humans, and whether or not other immunomodulators might play a role. AMs were isolated from bronchoalveolar lavage (BAL) fluid from either mice or humans, and cocultured with enriched naive CD4(+)FoxP3(-) T cells. We show here for the first time that AMs and AM-conditioned media (AM-CM) from mice and humans induced FoxP3 expression in naive CD4(+) T cells in vitro, an outcome that was reversed in part either by inhibiting retinoic acid (RA) binding to its receptor (RAR), or by blocking transforming growth factor (TGF)-β₁ signaling. A nasal administration of the RAR antagonist reduced the frequencies of CD4(+)FoxP3(+) T cells in the lungs of mice after aerosol challenge with Bordetella pertussis. In addition, we found that the intranasal vaccination of mice with ovalbumin (OVA) protein in conjunction with an RAR inhibitor led to a significant increase in OVA-specific serum IgE. Our findings suggest that AMs can mediate tolerance in the lungs of mice and humans via RA and TGF-β₁. These data may have implications in the development of nasal vaccines in the future.

Chemokines and their receptors in the allergic airway inflammatory process

The development of the allergic airway disease conveys several cell types, such as T-cells, eosinophils, mast cells, and dendritic cells, which act in a special and temporal synchronization. Cellular mobilization and its complex interactions are coordinated by a broad range of bioactive mediators known as chemokines. These molecules are an increasing family of small proteins with common structural motifs and play an important role in the recruitment and cell activation of both leukocytes and resident cells at the allergic inflammatory site via their receptors. Trafficking and recruitment of cell populations with specific chemokines receptors assure the presence of reactive allergen-specific T-cells in the lung, and therefore the establishment of an allergic inflammatory process. Different approaches directed against chemokines receptors have been developed during the last decades with promising therapeutic results in the treatment of asthma. In this review we explore the role of the chemokines and chemokine receptors in allergy and asthma and discuss their potential as targets for therapy.

Pivotal Advance: Nonfunctional lung effectors exhibit decreased calcium mobilization associated with reduced expression of ORAI1

CD8(+) T cells play a critical role in the clearance of respiratory pathogens. Thus, it is surprising that functional inactivation of lung effectors has been observed in many models of viral infection. Currently, the molecular defect responsible for the shut-off of function in these cells is unknown. In the present study, we addressed this question using a model of respiratory infection with the paramyxovirus SV5. Nonfunctional cells were found to exhibit decreases in SOCE, resulting in reduced NFAT1 activation. Notably, function could be restored by the provision of increased levels of extracellular calcium. The reduced ability to mobilize calcium was associated with reduced expression of ORAI1, the CRAC channel subunit. These findings reveal a previously unknown mechanism for the negative regulation of function in effector T cells.

Trafficking, persistence, and activation state of adoptively transferred allogeneic and autologous Simian Immunodeficiency Virus-specific CD8(+) T cell clones during acute and chronic infection of rhesus macaques

Despite multiple lines of evidence suggesting their involvement, the precise role of CD8(+) T cells in controlling HIV replication remains unclear. To determine whether CD8(+) T cells can limit retroviral replication in the absence of other immune responses, we transferred 1-13 x 10(9) allogeneic in vitro expanded SIV-specific CD8(+) T cell clones matched for the relevant restricting MHC-I allele into rhesus macaques near the time of i.v. SIV challenge. Additionally, in vitro expanded autologous SIV-specific CD8(+) T cell clones were infused 4-9 mo postinfection. Infused cells did not appreciably impact acute or chronic viral replication. The partially MHC-matched allogeneic cells were not detected in the blood or most tissues after 3 d but persisted longer in the lungs as assessed by bronchoalveolar lavage (BAL). Autologous cells transferred i.v. or i.p. were found in BAL and blood samples for up to 8 wk postinfusion. Interestingly, despite having a nominally activated phenotype (CD69(+)HLA-DR(+)), many of these cells persisted in the BAL without dividing. This suggests that expression of such markers by T cells at mucosal sites may not reflect recent activation, but may instead identify stable resident memory T cells. The lack of impact following transfer of such a large number of functional Ag-specific CD8(+) T cells on SIV replication may reflect the magnitude of the immune response required to contain the virus.

Respiratory Homeostasis and Exploitation of the Immune System for Lung Cancer Vaccines

Lung cancer is the leading cause of all cancer deaths in the US. The international scientific and clinical community has made significant advances toward understanding specific molecular mechanisms underlying lung carcinogenesis; however, despite these insights and advances in surgery and chemoradiotherapy, the prognosis for non-small-cell lung cancer (NSCLC) remains poor. Nonetheless, significant effort is being focused on advancing translational research evaluating the efficacy of novel targeted therapeutic strategies for lung cancer. Illustrative examples of this include antagonists of the epidermal growth factor receptor (EGFR), tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib, and a diverse assortment of anti-angiogenic compounds targeting growth factors and/or their receptors that regulate tumor-associated angiogenic programs. In addition, with the increased awareness of the significant role chronically activated leukocytes play as potentiators of solid-tumor development, the role of innate and adaptive immune cells as regulators of lung carcinogenesis is being examined. While some of these studies are examining how novel therapeutic strategies may enhance the efficacy of lung cancer vaccines, others are evaluating the intrinsic characteristics of the immune response to lung cancer in order to identify rate-limiting molecular and/or cellular programs to target with novel anticancer therapeutics. In this article, we explore important aspects of the immune system and its role in regulating normal respiratory homeostasis compared with the immune response accompanying development of lung cancer. These hallmarks are then discussed in the context of recent efforts to develop lung cancer vaccines, where we have highlighted important concepts that must be taken into consideration for future development of novel therapeutic strategies and clinical trials assessing their efficacy.

T cell trafficking in allergic asthma: the ins and outs

T cells are critical mediators of the allergic airway inflammation seen in asthma. Pathogenic allergen-specific T cells are generated in regional lymph nodes and are then recruited into the airway by chemoattractants produced by the asthmatic lung. These recruited effector T cells and their products then mediate the cardinal features of asthma: airway eosinophilia, mucus hypersecretion, and airway hyperreactivity. There has been considerable progress in delineating the molecular mechanisms that control T cell trafficking into peripheral tissue, including the asthmatic lung. In this review, we summarize these advances and formulate them into a working model that proposes that T cell trafficking into and out of the allergic lung is controlled by several discrete regulatory pathways that involve the collaboration of innate and acquired immune cells.

High levels of endogenous nitric oxide produced after burn injury in rats arrest activated T lymphocytes in the first G1 phase of the cell cycle and then induce their apoptosis

Major physical traumas provoke a systemic inflammatory response and immune dysfunction. In a model of thermal injury in rats, we previously showed that an overproduction of nitric oxide (NO) was responsible for the collapse of lymphoproliferative responses. In the present work, we performed a time-course analysis of cell proliferation and cell death parameters in order to establish the sequence of events triggered by the high NO output in Wistar/Han rat splenocytes activated with Con A, 10 days after burn injury. We demonstrate that activated T cells from burned rats never divided whereas normal T cells underwent four division cycles. However, T cells from both burned and normal rat entered the G1 phase as shown by increase of cell size, mitochondria hyperpolarization, and expression of cyclin D1. Burned rat T cells progressed to the late G1 phase as shown by expression of the nuclear Ki-67 antigen, but they never entered the S phase. They underwent apoptosis as shown by morphological parameters, disruption of transmembrane mitochondrial potential, and DNA fragmentation. Persistent accumulation of the p53 protein accompanied these phenomena. NO synthase inhibitors antagonize alterations of cell proliferation and cell death parameters in burned rat T cells and accelerated p53 turnover.

Characterization of a B220+Lymphoid Cell Subpopulation with Immune Modulatory Functions in Nasal-Associated Lymphoid Tissues

Complex mechanisms operate on mucosal tissues to regulate immune responsiveness and tolerance. When the lymphocyte subpopulations from murine nasal-associated lymphoid tissues (NALT) were characterized, we observed an accumulation of B220(low)CD3(low)CD4(-)CD8(-)CD19(-)c-Kit(+) cells. TCR transgenic mice and athymic mice were used for monitoring T cell lineage and the presence of extrathymic T cell precursors. The majority of cells from NALT exhibited a T cell precursor phenotype (CD4(-)CD8(-)CD19(-)c-Kit(+)). Fas-independent apoptosis was their main mechanism of cell death. We also demonstrated that B220(low)CD4(-)CD8(-)CD19(-) cells from NALT exhibited the potential to down-regulate the activation of mature T cells. However, the innate immunity receptor TLR2 was also highly expressed by this cell subpopulation. Moreover, nasal stimulation with a TLR2/6 agonist resulted in a partial activation of the double-negative cells. These results suggest that the immune responses in NALT may be in part modulated by a cell subpopulation that maintains a tolerogenic milieu by its proapoptotic status and suppressive activity, which can be reverted through stimulation of a TLR signaling cascade.

Bidirectional interactions between antigen-bearing respiratory tract dendritic cells (DCs) and T cells precede the late phase reaction in experimental asthma: DC activation occurs in the airway mucosa but not in the lung parenchyma

The airway mucosal response to allergen in asthma involves influx of activated T helper type 2 cells and eosinophils, transient airflow obstruction, and airways hyperresponsiveness (AHR). The mechanism(s) underlying transient T cell activation during this inflammatory response is unclear. We present evidence that this response is regulated via bidirectional interactions between airway mucosal dendritic cells (AMDC) and T memory cells. After aerosol challenge, resident AMDC acquire antigen and rapidly mature into potent antigen-presenting cells (APCs) after cognate interactions with T memory cells. This process is restricted to dendritic cells (DCs) in the mucosae of the conducting airways, and is not seen in peripheral lung. Within 24 h, antigen-bearing mature DCs disappear from the airway wall, leaving in their wake activated interleukin 2R+ T cells and AHR. Antigen-bearing activated DCs appear in regional lymph nodes at 24 h, suggesting onward migration from the airway. Transient up-regulation of CD86 on AMDC accompanies this process, which can be reproduced by coculture of resting AMDC with T memory cells plus antigen. The APC activity of AMDC can be partially inhibited by anti-CD86, suggesting that CD86 may play an active role in this process and/or is a surrogate for other relevant costimulators. These findings provide a plausible model for local T cell activation at the lesional site in asthma, and for the transient nature of this inflammatory response.

Cellular immunity and memory to respiratory virus infections

Respiratory virus infections, such as those caused by influenza and parainfluenza viruses, are a major cause of morbidity and mortality worldwide. Current vaccines against these pathogens rely on the induction of humoral immune responses that target viral coat proteins. Although this type of immunity provides solid protection against homologous virus strains, it is ineffective against heterologous virus strains that express serologically distinct coat proteins. In contrast, cellular immune responses can target internal antigens that are shared between heterologous viral strains. This form of immunity, sometimes referred to as heterosubtypic immunity, can mediate a substantial degree of protection. Thus, vaccines that emphasize cellular immune responses would be a valuable complement to available humoral vaccines. However, we only have a rudimentary understanding of which T cell subsets mediate protective immunity, how T cell memory is established and maintained, how that memory is recalled in a secondary infection, and why cellular immunity wanes rapidly with time. Here we review the role of CD4+ and CD8+ T cells in the recall response to influenza and parainfluenza viruses. In particular we focus on the recent observation that substantial numbers of memory T cells are established in the lung tissues and discuss the potential role of these cells in mediating a recall response. A thorough understanding of the cellular immune response to infection in the lungs is essential for future vaccine development.

Naive and memory T cells migrate in comparable numbers through the normal rat lung: only effector T cells accumulate and proliferate in the lamina propria of the bronchi

T cells reach the lung via the pulmonary and bronchial arteries that supply the alveolar and bronchial regions. Although these regions are differentially affected by T cell-mediated diseases, the migration of T-cell subsets in these two regions has not been studied. Naive, memory, and effector T cells were injected into congenic rats and traced in sections of normal lung. All three T-cell subsets were found in large numbers in the alveolar region and exited again quickly. Only effector T cells accumulated in the lamina propria of the bronchi. Further, 72 h after injection 6% of the effector T cells still proliferated in the lung, whereas apoptotic effector T cells were only observed 1 h after injection (0.2%). Thus, not only effector and memory but also naive T cells continuously migrated through the lung. The preferential accumulation of effector T cells in the bronchial lamina propria may explain why some diseases preferentially affect the bronchial region.

Effects of cyclosporin A administered into the airways against antigen-induced airway inflammation and hyperreactivity in the rat

The immunosuppressant cyclosporin A given orally has anti-asthma properties but carries an undesirable risk of systemic effects. We administered cyclosporin A to Brown Norway rats either orally (p.o.) or topically by intratracheal (i.t.) instillation into the airways before inhaled antigen. Cyclosporin A suppressed the antigen-induced accumulation of activated (CD25+) CD4+ T lymphocytes and eosinophils in the lung, interleukin-5 mRNA expression in lung tissue and airway hyperreactivity. Intratracheal cyclosporin A suppressed cell accumulation at a 10-fold lower dose than that required orally. Minimum effective doses were 3 mg x kg(-1) i.t. and 30 mg x kg(-1) p.o. Intratracheal administration reduced the plasma concentration and systemic exposure compared with an equieffective oral dose, but the reduction (4-5-fold) was not as large as anticipated. Our data suggests that although topical administration to asthmatics would provide some potential for an improved safety margin, it may not offer any major advantage over existing oral therapy. However, the data clearly demonstrate that a novel immunosuppressant with similar anti-inflammatory properties but reduced potential for systemic effects would offer an attractive therapy for severe asthma.

T cell phenotypes of the normal nasal mucosa: induction of Th2 cytokines and CCR3 expression by IL-4

Mucosal environments such as that of the nose are points of first contact between the human organism and its environment. At these sites the immune system must be regulated to differentiate between and respond appropriately to pathogens and harmless contaminants. T cell-driven immune responses broadly fall into Th1- or Th2-type phenotypes, with increasing evidence that the recruitment of these T lymphocyte subsets is mediated by selective expression of specific chemokine receptors. We have investigated the immunology of the normal nasal mucosa. We show that nasal T cell lines from normal individuals, expanded by culture in IL-2, show reduced expression of the Th2-type cytokines IL-4 and IL-5 compared with lines derived from the blood of the same subjects. These T cells also show reduced expression of the Th2-selective chemokine receptor, CCR3, but similar levels of CCR4 compared with the blood-derived lines. This apparent suppression of Th2 cytokine and CCR3 expression by nasal T cells was reversed by addition of IL-4 to the culture medium. These data are consistent with the presence of a nasal mucosal microenvironment that suppresses Th2 responses and may represent a protective measure against atopic allergic disease in humans and a favoring of Th1 responses to infectious agents. In contrast, T cell expression of CCR1 was higher in the nose than in the blood regardless of the culture medium cytokine environment in keeping with a role for this receptor in tissue homing or lymphocyte activation.

Activated antigen-specific CD8+ T cells persist in the lungs following recovery from respiratory virus infections

The poor correlation between cellular immunity to respiratory virus infections and the numbers of memory CD8(+) T cells in the secondary lymphoid organs suggests that there may be additional reservoirs of T cell memory to this class of infection. Here we identify a substantial population of Ag-specific T cells in the lung that persist for several months after recovery from an influenza or Sendai virus infection. These cells are present in high numbers in both the airways and lung parenchyma and can be distinguished from memory cell populations in the spleen and peripheral lymph nodes in terms of the relative frequencies among CD8(+) T cells, activation status, and kinetics of persistence. In addition, these cells are functional in terms of their ability to proliferate, express cytolytic activity, and secrete cytokines, although they do not express constitutive cytolytic activity. Adoptive transfer experiments demonstrated that the long-term establishment of activated T cells in the lung did not require infection in the lung by a pathogen carrying the inducing Ag. The kinetics of persistence of Ag-specific CD8(+) T cells in the lung suggests that they play a key role in protective cellular immunity to respiratory virus infections.

A critical role for alveolar macrophages in elicitation of pulmonary immune fibrosis

Hapten immune pulmonary interstitial fibrosis (HIPIF) is induced by a recall cell-mediated immune response against the hapten 2,4, 6-trinitrobenzene sulphonic acid (TNBS) in the lung. Studies here dissect the role of the cellular components of the bronchoalveolar lavage (BAL) cells (alveolar macrophages [AMs] versus monocytes and immature dendritic cells) in the fibrogenic inflammatory response. BAL cells from HIPIF mice were generally more activated and produced a greater amount of tumour necrosis factor-alpha (TNF-alpha) than controls. Liposome-encapsulated dichloromethylene diphosphonate (Cl(2)MDP) that was inoculated intranasally (i.n.) into mice selectively depleted AMs. Following AM depletion, the number of TNF-alpha-containing cells was reduced, and both the number of immune inflammatory cells recruited into the alveolar space and the subsequent collagen deposition (hydroxyproline) were decreased in the sensitized and intratracheally (i.t.) challenged mice. In conclusion, AMs are required, in part, for the development of pulmonary fibrosis in HIPIF because AM-derived factors such as TNF-alpha are needed for initiation of chemokine and cytokine pathways and accumulation of immune inflammatory cells.

Lymphocyte-endothelial cell adhesive interactions in lung immunity: lessons from the murine response to particulate antigen

The adhesive interaction between lymphocytes and lung endothelial cells presents an attractive arena for the development of novel therapeutic agents to modify pathologic pulmonary immune responses. The conceptual basis for choosing molecular targets to modulate this adhesive interaction derives, in large part, from results of murine experimental model systems of the pulmonary immune response. This article reviews one such model, the response of primed C57BL/6 mice to the particulate antigen sheep erythrocytes. Novel data are presented on the effect of a blocking anti-alpha(4) integrin monoclonal antibody on lung leukocyte and lymphocyte subset accumulation after intratracheal (IT) antigen challenge. Results from this model system have indicated that lymphocytes may use either the endothelial selectins or alpha(4) integrin as independent pathways to initiate recruitment into the lungs.

Regulation by human uterine cells of PBMC proliferation: influence of the phase of the menstrual cycle and menopause

To determine the influence of human uterine cells recovered at different stages of the menstrual cycle and following menopause on the proliferation of peripheral blood mononuclear cells (PBMC), whole cell suspensions of uterine tissues were co-cultured with autologous and heterologous PBMC. PBMC proliferation in response to tetanus toxoid (TT) or Con A was inhibited by uterine endometrial cells and was dependent on the phase of the menstrual cycle. Inhibition by cells from the proliferative phase was significantly greater than by cells from the secretory phase. Uterine cells isolated from post-menopausal women also inhibited proliferation of PBMC. Cell fractionation studies indicated that epithelial cells are the primary source of uterine inhibitory activity. When epithelial cells and PBMC were cultured in separate compartments, epithelial cells released a soluble factor(s) that inhibited the PBMC proliferation. These results suggest that uterine epithelial cells produce cytokines that down-regulate the proliferation of PBMC in response to antigens and mitogens. This may be important for the control of uterine immune responses, as well as the growth of the reproductive tract in preparation for implantation during the secretory phase of the menstrual cycle.

An ex vivo study of T lymphocytes recovered from the lungs of I/St mice infected with and susceptible to Mycobacterium tuberculosis

I/St mice, previously characterized as susceptible to Mycobacterium tuberculosis H37Rv, were given 10(3) or 10(5) CFU intravenously. At two time points postinoculation, the cell suspensions that resulted from enzymatic digestion of lungs were enumerated and further characterized phenotypically and functionally. Regarding the T-cell populations recovered at 2 and 5 weeks postinfection, two main results were obtained: (i) the population of CD44(-) CD45RB+ cells disappeared within 2 weeks postinfection, while the number of CD44(+) CD45RB-/low cells slowly increased between weeks 2 and 5; (ii) when cocultured with irradiated syngeneic splenocytes, these lung T cells proliferated in the presence of H37Rv sonicate. Using H37Rv sonicate and irradiated syngeneic splenocytes to reactivate lung T cells, we selected five CD3(+) CD4(+) CD8(-) T-cell clones. In addition to the H37Rv sonicate, the five clones react to both a short-term culture filtrate and an affinity-purified 15- to 18-kDa mycobacterial molecule as assessed by the proliferative assay. However, there was a clear difference between T-cell clones with respect to cytokine (gamma interferon [IFN-gamma] and interleukin-4 [IL-4] and IL-10) profiles: besides one Th1-like (IFN-gamma+ IL-4(-)) clone and one Th0-like (IFN-gamma+ IL-4(+) IL-10(+)) clone, three clones produced predominantly IL-10, with only marginal or no IL-4 and IFN-gamma responses. Inhibition of mycobacterial growth by macrophages in the presence of T cells was studied in a coculture in vitro system. It was found that the capacity to enhance antimycobacterial activity of macrophages fully correlated with INF-gamma production by individual T-cell clones following genetically restricted recognition of infected macrophages. The possible functional significance of cytokine diversity among T-cell clones is discussed.

Macrophage-Derived Nitric Oxide Regulates T Cell Activation via Reversible Disruption of the Jak3/STAT5 Signaling Pathway

Nitric oxide (NO) has been invoked as an important pathogenic factor in a wide range of immunologically mediated diseases. The present study demonstrates that macrophage-derived NO may conversely function to fine tune T cell-mediated inflammation via reversible dephosphorylation of intracellular signaling molecules, which are involved in the control of T cell proliferation. Thus, T cells activated in the presence of alveolar macrophages are unable to proliferate despite expression of IL-2R and secretion of IL-2. This process is reproduced by the NO generator S-nitroso-N-acetylpenicillamine and is inhibitable by the NO synthase inhibitor NG-methyl-l-arginine. Analysis of T cell lysates by immunoprecipitation with specific Abs and subsequent immunoblotting indicated marked reduction of tyrosine phosphorylation of Jak3 and STAT5 mediated by NO. Further studies indicated that NO-mediated T cell suppression was reversible by the guanylate cyclase inhibitors methylene blue and LY-83583 and was reproduced by a cell-permeable analogue of cyclic GMP, implicating guanylate cyclase activation as a key step in the inhibition of T cell activation by NO.

Alveolar macrophages regulate the induction of primary cytotoxic T-lymphocyte responses during influenza virus infection

Virus-specific cytotoxic T lymphocytes (CTL) are thought to be responsible for the eradication of respiratory influenza virus infections by direct cytolysis of virus-infected epithelial cells. In this study, we provide evidence for a role for alveolar macrophages (AM) in the regulation of pulmonary virus-specific CTL responses. Prior to infection with influenza virus, AM were selectively eliminated in vivo with a liposome-mediated depletion technique, and virus-specific CTL activities of lung and mediastinal lymph node (MLN) cells were assayed ex vivo and compared with those for normal mice. AM depletion resulted in increased primary CTL responses and changed the kinetics of the CTL response. Flow cytometric analysis of lung and MLN cells showed that the percentage of CD8+ cells was not altered after AM depletion and that lung cells from AM-depleted mice had an increased capacity to lyse virus-infected cells. Upon restimulation in vitro, virus-specific CTL activity in lung cells of normal mice was similar to that in lung cells of AM-depleted mice. Furthermore, elimination of AM resulted in increased virus titers in the lung, but virus clearance as a function of time was not affected. Our results show that AM regulate virus-specific CTL responses during respiratory influenza virus infection by removing viral particles, by downregulating the priming and activity of CTL in MLN cells, and by inhibiting the expansion of virus-specific CTL in the lung.

RPR 106541, a novel, airways-selective glucocorticoid: effects against antigen-induced CD4+ T lymphocyte accumulation and cytokine gene expression in the Brown Norway rat lung

1. The effects of a novel 17-thiosteroid, RPR 106541, were investigated in a rat model of allergic airway inflammation. 2. In sensitized Brown Norway rats, challenge with inhaled antigen (ovalbumin) caused an influx of eosinophils and neutrophils into the lung tissue and airway lumen. In the lung tissue there was also an accumulation of CD4+ T lymphocytes and increased expression of mRNA for interleukin-4 (IL-4) and IL-5, but not interferon-gamma (IFN-gamma). These findings are consistent with an eosinophilia orchestrated by activated Th2-type cells. 3. RPR 106541 (10-300 microg kg[-1]), administered by intratracheal instillation into the airways 24 h and 1 h before antigen challenge, dose-dependently inhibited cell influx into the airway lumen. RPR 106541 (100 microg kg[-1]) caused a significant (P<0.01) (98%) inhibition of eosinophil influx and a significant (P<0.01) (100%) inhibition of neutrophil influx. RPR 106541 was approximately 7 times and 4 times more potent than budesonide and fluticasone propionate, respectively. 4. When tested at a single dose (300 microg kg[-1]), RPR 106541 and fluticasone each caused a significant (P<0.01) (100%) inhibition of CD4+ T cell accumulation in lung tissue. Budesonide (300 microg kg[-1]) had no significant effect. RPR 106541 and fluticasone (300 microg kg[-1]), but not budesonide (300 microg kg[-1]), significantly (P<0.05) inhibited the expression within lung tissue of mRNA for IL-4. RPR 106541 (300 microg kg[-1]) also significantly (P<0.05) inhibited expression of mRNA for IL-5. 5. The high topical potency of RPR 106541 in this model, which mimics important aspects of airway inflammation in human allergic asthmatics, suggests that this glucocorticoid may be useful in the treatment of bronchial asthma.

Class II MHC expression on rat intestinal intraepithelial lymphocytes

The expression of class II major histocompatibility complex (MHC) on rat intestinal intraepithelial lymphocytes (IELs) and mesenteric lymph node cells (MLNCs) were examined by immunofluorescence and flow cytometry. As expected, MLNCs contain eight small populations of CD4+ class II MHC+ T-cells in addition to classical antigen presenting cells. In contrast, rat IELs include a significant population of class II MHC+ T-cells, predominantly in the CD8+ CD4-alpha beta TCR+ subset. IEL samples with a relatively high percentage of class II MHC+ cells also include some CD4+ class II MHC+ cells; IEL samples with a low percentage of class II MHC+ cells also include some CD4- CD8- class II MHC+ cells. The role of lymphocyte subpopulations in the intestinal epithelium may need to be revisited in consideration of these findings.