Characterization of suppressor function of human alveolar macrophages for T lymphocyte responses to phytohemagglutinin: cellular selectivity, reversibility, and early events in T cell activation

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.

Characteristics of suppressor macrophages induced by mycobacterial and protozoal infections in relation to alternatively activated M2 macrophages

In the advanced stages of mycobacterial infections, host immune systems tend to change from a Th1-type to Th2-type immune response, resulting in the abrogation of Th1 cell- and macrophage-mediated antimicrobial host protective immunity. Notably, this type of immune conversion is occasionally associated with the generation of certain types of suppressor macrophage populations. During the course of Mycobacterium tuberculosis (MTB) and Mycobacterium avium-intracellulare complex (MAC) infections, the generation of macrophages which possess strong suppressor activity against host T- and B-cell functions is frequently encountered. This paper describes the immunological properties of M1- and M2-type macrophages generated in tumor-bearing animals and those generated in hosts with certain microbial infections. In addition, this paper highlights the immunological and molecular biological characteristics of suppressor macrophages generated in hosts with mycobacterial infections, especially MAC infection.

Alveolar macrophage subpopulations in bronchoalveolar lavage and induced sputum of asthmatic and control subjects

BACKGROUND

Alveolar macrophages (AM) are the most numerous immune cells in the airways and are involved in the immunological homeostasis of the lung. Intriguingly, their role in asthma remains unclear probably, in part, because of their heterogeneity.

OBJECTIVE

To characterize AM population from bronchoalveolar lavage (BAL) and induced sputum (IS) of asthmatic and normal subjects using specific biomarkers.

METHODS

Non-asthmatic non-allergic and allergic mild asthmatic subjects were recruited for this study. AM were obtained from BAL and IS and cytospins were prepared. Immunocytochemistry was performed for nine cellular markers (CD68, RFD7, CD14, CD11b, CD83, CD64, CD80, CD86, and FIZZ1).

RESULTS

Asthmatic subjects had more AM RFD7(+) in BAL compared with IS, whereas control subjects had more AM RFD7(+) in IS than in BAL. Consequently, there was an increased number of AM RFD7(+) in BAL of asthmatic subjects compared with BAL of control subjects. AM CD11b(+) was higher in BAL than in IS in both groups. The expression of FIZZ1, marker of macrophage alternative activation, was similar in asthmatic and normal subjects.

CONCLUSION

The expression of cellular markers on AM differs according to their localization in the lung. Subpopulations of AM may contribute to the inflammatory profile observed in asthmatic subjects.

Innate immune mechanism in allergic asthma

Allergic asthma is a chronic inflammatory disorder of the airways characterized by eosinophilic inflammation, airway hyperresponsiveness, and mucus hypersecretion. Adaptive, antigen-dependent immunity is critical for asthma pathogenesis. Allergic asthma may involve adaptive and innate, antigen-independent immune responses. This review discusses the current evidence that associates innate immunity with allergic asthma pathogenesis. In particular, we focus on the role of innate immune cells (eg, bronchial epithelial cells, alveolar macrophages, and dendritic cells) and molecules (Toll-like and nucleotide-binding oligomerization domain-like receptors) in modifying allergic immune responses.

Airway cell and cytokine changes in early asthma deterioration after inhaled corticosteroid reduction

BACKGROUND

Back-titration of inhaled corticosteroid (ICS) dose in well-controlled asthma patients is emphasized in clinical guidelines, but there are few published data on the airway cell and cytokine changes in relation to ICS reduction. In our study, 20 mild-to-moderate persistent (inspite of low-moderate dose ICS treatment) asthmatic subjects prospectively rendered largely asymptomatic by high-dose ICS were assessed again by clinical, physiological, and airway inflammatory indices after 4-8 weeks of reduced ICS treatment. We aimed at assessing the underlying pathological changes in relation to clinical deterioration.

METHODS

Patients recorded daily symptom scores and peak expiratory flows (PEF). Spirometry and airways hyperreactivity (AHR) were measured and bronchoscopy was performed with assessment of airway biopsies (mast cells, eosinophils, neutrophils, and T lymphocytes), bronchoalveolar lavage (BAL) IL-5 and eotaxin levels and cellular profiles at the end of high-dose ICS therapy and again after ICS dose reduction. Baseline data were compared with symptomatic steroid-free asthmatics (n=42) and non-asthmatic controls (n=28).

RESULTS

After ICS reduction, subjects experienced a variable but overall significant increase in symptoms and reductions in PEF and forced expiratory volume in 1 s. There were no corresponding changes in AHR or airways eosinophilia. The most relevant pathogenic changes were increased CD4(+)/CD8(+) T cell ratio, and decreased sICAM-1 and CD18 macrophage staining (potentially indicating ligand binding). However, there was no relationship between the spectrum of clinical deterioration and the changes in cellular profiles or BAL cytokines.

CONCLUSIONS

These data suggest that clinical markers remain the most sensitive measures of early deterioration in asthma during back-titration of ICS, occurring at a time when AHR and conventional indices of asthmatic airway inflammation appear unchanged. These findings have major relevance to management and to how back-titration of ICS therapy is monitored.

Antigen sensitization modulates alveolar macrophage functions in an asthma model

We have previously demonstrated that adoptive transfer of alveolar macrophages from allergy-resistant rats to alveolar macrophage-depleted allergic rats prevents airway hyperresponsiveness development, suggesting an important role for alveolar macrophages in asthma pathogenesis. Given that ovalbumin sensitization can modulate alveolar macrophage cytokine production, we investigated the role of sensitized and unsensitized alveolar macrophages in an asthma model. Alveolar macrophages from unsensitized or sensitized Brown Norway rats were transferred to alveolar macrophage-depleted sensitized rats 24 h before allergen challenge. Airway responsiveness to methacholine and airway inflammation were measured the following day. Methacholine concentration needed to increase lung resistance by 200% was significantly higher in alveolar macrophage-depleted sensitized rats that received unsensitized alveolar macrophages compared with alveolar macrophage-depleted sensitized rats that received sensitized alveolar macrophages. Tumor necrosis factor levels in bronchoalveolar lavage fluid of sensitized rats that received unsensitized alveolar macrophages were significantly lower compared with rats that received sensitized alveolar macrophages. Interestingly, alveolar macrophages of unsensitized animals showed higher phagocytosis activity compared with alveolar macrophages of sensitized rats, suggesting that sensitization modulates alveolar macrophage phagocytosis function. Our data suggest an important role of allergen sensitization on alveolar macrophage function in asthma pathogenesis.

Inhibition of major histocompatibility complex II expression and antigen processing in murine alveolar macrophages by Mycobacterium bovis BCG and the 19-kilodalton mycobacterial lipoprotein

Alveolar macrophages constitute a primary defense against Mycobacterium tuberculosis, but they are unable to control M. tuberculosis without acquired T-cell immunity. This study determined the antigen-presenting cell function of murine alveolar macrophages and the ability of the model mycobacterium, Mycobacterium bovis BCG, to modulate it. The majority (80 to 85%) of alveolar macrophages expressed both CD80 (B7.1) and CD11c, and 20 to 30% coexpressed major histocompatibility complex II (MHC-II). Gamma interferon (IFN-gamma) enhanced MHC-II but not B7.1 expression. Naive or IFN-gamma-treated alveolar macrophages did not express CD86 (B7.2), CD11b, Mac-3, CD40, or F4/80. M. bovis BCG and the 19-kDa mycobacterial lipoprotein inhibited IFN-gamma-regulated MHC-II expression on alveolar macrophages, and inhibition was dependent on Toll-like receptor 2. The inhibition of MHC-II expression by the 19-kDa lipoprotein was associated with decreased presentation of soluble antigen to T cells. Thus, susceptibility to tuberculosis may result from the ability of mycobacteria to interfere with MHC-II expression and antigen presentation by alveolar macrophages.

Adoptive transfer of alveolar macrophages abrogates bronchial hyperresponsiveness

Increasing evidence suggests that alveolar macrophages (AM) are involved in asthma pathogenesis. To better understand the role that these cells play, we investigated the capacity of AM from allergy-resistant rat, Sprague Dawley (SD), to modulate airway hyperresponsiveness of allergy-susceptible rat, Brown Norway (BN). AM of ovalbumin (OVA)-sensitized BN rats were eliminated by intratracheal instillation of liposomes containing clodronate. AM from OVA-sensitized SD rats were transferred into AM-depleted BN rats 24 h before allergen challenge. Airway responsiveness to methacholine was measured the following day. Instillation of liposomes containing clodronate in BN rats eliminated 85% AM after 3 d compared with saline liposomes. Methacholine concentration needed to increase lung resistance by 200% (EC200RL) was significantly lower in OVA-challenged BN rats (27.9 +/- 2.8 mg/ml) compared with SD rats (63.9 +/- 8.6 mg/ml). However, when AM from SD rats were transferred into AM-depleted BN rats, airway responsiveness (64.0 +/- 11.3 mg/ml) was reduced to the level of naïve rats (54.4 +/- 3.7 mg/ml) in a dose-dependent manner. Interestingly, transfer of AM from BN rats into SD rats did not modulate airway responsiveness. To our knowledge, this is the first direct evidence showing that AM may protect against the development of airway hyperresponsiveness.

House dust mite Dermatophagoides farinae augments proinflammatory mediator productions and accessory function of alveolar macrophages: implications for allergic sensitization and inflammation

In this study, we examine the effects of Dermatophagoides farinae (Der f), a major source of airborne allergens, on alveolar macrophages (AMs), and we also test its contribution to allergic responses in mice. Der f activated NF-kappaB of AMs and, unlike OVA or LPS stimulation, up-regulated IL-6, TNF-alpha, and NO. In addition, it down-regulated antioxidants, but affected neither the expression nor production of IL-12. Der f-stimulated AMs expressed enhanced levels of costimulatory B7 molecules, supported T cell proliferation, and promoted Th2 cell development. The enhanced accessory function was suppressed by blockade mAbs to B7.2, IL-6, and TNF-alpha and by N-monomethyl-L-arginine, an NO synthase inhibitor, and N-acetylcysteine, a thiol antioxidant, whereas it was augmented by (+/-)-S-nitroso-N-acetylpenicillamine, an NO donor. Arg-Gly-Asp-Ser peptide and neo-glycoproteins galactose-BSA and mannose-BSA inhibited the Der f-induced IL-6 and TNF-alpha productions and enhanced accessory function of AMs. Der f was more potent than OVA for inducing pulmonary eosinophilic inflammation, NO, and serum allergen-specific IgG1 Ab production in mice. AMs from Der f-challenged mice expressed enhanced levels of B7 and augmented T cell proliferation ex vivo. In Der f-challenged mice, respiratory syncytial virus infection (5 x 10(5) pfu; 3 days before Der f instillation) augmented Der f-specific Ab production, whereas dexamethasone (50 mg/kg; 1 h before Der f instillation) diminished the allergic airway inflammation and Ab response. We conclude that AMs are sensitive targets for Der f and that the Der f-induced proinflammatory responses may represent an important mechanism in mediating the development of allergic sensitization and inflammation.

Mycobacterium tuberculosis-infected human macrophages exhibit enhanced cellular adhesion with increased expression of LFA-1 and ICAM-1 and reduced expression and/or function of complement receptors, FcgammaRII and the mannose receptor

The entry of Mycobacterium tuberculosis (Mtb) into the host macrophage and its survival in this environment are key components of tuberculosis pathogenesis. Following intracellular replication of the bacterium within alveolar macrophages, there is spread of bacilli to regional lymph nodes in the lungs and subsequent presentation of antigens to the host immune system. How this process occurs remains poorly understood, but one mechanism may involve the migration of macrophages containing Mtb across the alveoli to lymph nodes, where there is development of a protective host response with formation of granulomas composed in part of aggregated and fused, apoptotic, infected macrophages. Leukocyte integrins, including lymphocyte function-associated antigen-1 (LFA-1) and complement receptors CR3 and CR4, and their counter receptors play a major role in macrophage adhesion processes and phagocytosis. In this study, the appearance of Mtb-infected macrophages over time was examined, using inverted-phase microscopy and an in vitro culture model of human monocyte-derived macrophages (MDMs). Prior to and immediately following infection of the MDMs with Mtb, the macrophages appeared as individual cells in monolayer culture; however, within 24 h of infection with Mtb, the MDMs began to migrate and adhere to each other. The kinetics of this response were dependent on both the m.o.i. and the length of infection. Quantitative transmission electron microscopy studies revealed that macrophage adhesion was accompanied by increases in levels of LFA-1 and its counter receptor (ICAM-1), decreases in surface levels of the phagocytic receptors CR3, CR4 and FcgammaRII, and an increase in major histocompatibility complex Class II (MHC-II) molecules at 72 h post-infection. Decreases in surface levels of CR3 and CR4 had a functional correlate, with macrophages containing live bacilli showing a diminished phagocytic capacity for complement-opsonized sheep erythrocytes; macrophages containing heat-killed bacilli did not show this diminished capacity. The modulation of macrophage adhesion and phagocytic proteins may influence the trafficking of Mtb-infected macrophages within the host, with increases in levels of LFA-1 and ICAM-1 enhancing the adhesive properties of the macrophage and decreases in phagocytic receptors diminishing the phagocytic capacity of an already-infected cell, potentially allowing for maintenance of the intracellular niche of Mtb.

Characterization of lung hyperresponsiveness, inflammation, and alveolar macrophage mediator production in allergy resistant and susceptible rats

To better understand asthma pathogenesis, we characterized airway responsiveness, lung inflammation, and mediator production of alveolar macrophages (AM) after allergen sensitization and challenge in two strains of rats showing different susceptibilities in developing airway allergic reactions. Airway responsiveness to acethylcholine was measured 24 h after ovalbumin (OVA) challenge, whereas bronchoalveolar lavages were performed 5 min, 8 h, and 24 h after challenge. Brown Norway rats showed airway hyperresponsiveness after challenge, whereas lung resistance remained unchanged in Sprague-Dawley rats. Interestingly, Sprague-Dawley rats developed a neutrophilic inflammation, whereas both neutrophils and eosinophils were increased in Brown Norway rats. AM mediator production varied with time with a lower tumor necrosis factor (TNF) and interleukin (IL)-10 release at 8 h after challenge. OVA challenge stimulated spontaneous TNF and IL-10 release by AM isolated 24 h after challenge in both strains of rats, although AM from Brown Norway rats released significantly more IL-10 and TNF. Furthermore, nitric oxide production was increased only in OVA-challenged (24 h) Brown Norway rats. Our results suggest that AM may participate to the expansion of Th2 inflammation in Brown Norway rats and that differences in AM mediator production may explain, in part, distinct allergic susceptibilities in these two strains of rats.

Interleukin-10 contributes development of macrophage suppressor activities by macrophage colony-stimulating factor, but not by granulocyte-macrophage colony-stimulating factor

Macrophages are known to possess suppressor activities in immune responses. To determine the effects of GM-CSF and M-CSF on the expression of macrophage suppressor activities, monocyte-derived macrophages cultured with GM-CSF (GM-Mphis) were compared with those cultured with M-CSF (M-Mphis) for antigen-specific proliferation and interferon-gamma (IFN-gamma) production by lymphocytes. Both GM-Mphis and M-Mphis equally suppressed lymphocyte proliferation, but only M-Mphis suppressed IFN-gamma production in response to purified protein derivative (PPD). M-Mphis, but not GM-Mphis, released IL-10 not only in the course of macrophage differentiation but also in response to PPD after maturation to macrophages. From the results that (i) exogenous IL-10 suppressed IFN-gamma production, but not proliferation of lymphocytes, and that (ii) neutralizing antibody to IL-10 reversed suppressor activities of M-Mphis on IFN-gamma production, but not lymphocyte proliferation, it appeared that IL-10 was the major factor responsible for suppression of IFN-gamma production. Thus, these results suggest that only M-CSF augments IL-10-dependent suppressor activity of macrophages on IFN-gamma production and that both GM-CSF and M-CSF induce IL-10-independent macrophage suppressor activity on lymphocyte proliferation.

Alveolar macrophages of allergic resistant and susceptible strains of rats show distinct cytokine profiles

Brown Norway rats are widely used as a model of asthma, whereas Sprague Dawley rats do not develop allergic reactions under the same conditions. Given the importance of alveolar macrophages (AM) in down-regulating cellular immune responses in the lung, we postulated that the different susceptibilities in the development of airway allergic reactions in these rat strains may be related to functional differences in their AM. We investigated the production of important mediators in asthma, namely tumour necrosis factor (TNF), interleukin-10 (IL-10), IL-12, IL-13, nitric oxide (NO) and macrophage inflammatory protein-1alpha (MIP-1alpha), by AM of unsensitized Sprague Dawley and Brown Norway rats. AM were purified by adherence and stimulated with OX8 (anti-CD8 antibody) or LPS. OX8 stimulation significantly increased the release of TNF, IL-10 and NO in both strains of rats, whereas MIP-1alpha and IL-12 release were increased in Brown Norway rats only. Interestingly, stimulated AM from Sprague Dawley rats released significantly more TNF and less IL-10, IL-12, IL-13, MIP-1alpha and NO compared with AM from Brown Norway rats. These differences were also observed at the mRNA level, except for TNF. Thus, AM from Brown Norway and Sprague Dawley rats are functionally different. Furthermore, LPS- and OX8-stimulated AM from Brown Norway rats produce more Th2 type cytokines (IL-10 and IL-13) than AM from Sprague Dawley rats, suggesting that these cells may play an important role in creating a cytokine milieu that may favour the development of allergic reactions.

Activation-inactivation of HIV-1 in the lung

The lung is prominently afflicted during the course of HIV-1 disease by both infectious and noninfectious complications. Direct or indirect effects of HIV-1 are likely central to the pathogenesis of these complications. Thus, any changes in viral load locally would negatively impact on the lung. This review focuses on the endogenous influences (immune effector cells, surfactant) and the exogenous factors (including infections such as tuberculosis and noninfectious exposures like cigarette smoke) that may contribute to activation or inactivation of HIV-1 in the lung.

Priming of alveolar macrophages by leukotriene D(4): potentiation of inflammation

Cysteinyl leukotrienes (LTs), including LTC(4), LTD(4), and LTE(4), are well known to induce bronchoconstriction and increase bronchial hyperreactivity, mucus secretion, and vascular permeability. Interestingly, alveolar macrophages (AMs) express LTD(4) high-affinity receptor. These cells represent a major source of inflammatory mediators implicated in the pathophysiology of asthma. Thus, we investigated the immunomodulatory effects of LTD(4) on the production of inflammatory mediators such as macrophage inflammatory protein (MIP)- 1alpha, tumor necrosis factor (TNF), and nitric oxide (NO) by AMs. NR8383 cells, an AM cell line, were pretreated with LTD(4) (10(-11) M) for different periods of time and stimulated or not with lipopolysaccharide (LPS) for 2 h. Although LTD(4) treatment did not modulate the release of MIP-1alpha and TNF, this treatment (6 h) significantly increased the release of these mediators when AMs were further stimulated with LPS (increases of 47 and 21%, respectively). Further, LTD(4) pretreatment increased messenger RNA (mRNA) levels of MIP-1alpha and TNF. These effects of LTD(4) were abrogated by the presence of a LTD(4) receptor antagonist, Verlukast (MK-679), showing the specificity of LTD(4). Interestingly, LTD(4) treatment significantly increased the release of NO by LPS-stimulated AMs without modulating mRNA levels of the inducible NO synthase. Our data suggest that LTD(4) primes AMs to release more MIP-1alpha, TNF, and NO after stimulation. Thus, in addition to its potent bronchoconstrictor effect, LTD(4) may participate in the inflammatory process seen in asthma by potentiating the production of proinflammatory mediators by AMs during immunologic stimuli.

Macrophage suppression of T cell activation: a potential mechanism of peripheral tolerance

The mechanisms of induction and maintenance of tolerance in self-reactive T cells in the periphery are poorly understood. Current models assume that successful T cell activation only occurs if ligation of the T cell receptor (signal 1) by antigen presenting cells (APCs) is accompanied by a costimulatory signal (signal 2), and that signal 1 in the absence of signal 2 is either ignored or is tolerizing. However, there is also evidence for the existence of macrophages (M phi) capable of suppressing T cell activation both in vitro and in vivo. The possibility of a more actively induced tolerance exists, in which the M phi itself responds to T cell-mediated signals in a tolerogenic fashion. This would help to resolve the paradox that tissue M phi, which act as scavengers of self-antigen, can also act as professional APCs. The ability of tissue macrophages to actively suppress T cells would further underscore the importance of the innate immune system in regulating adaptive immune responses.

Pulmonary immune responses during primary mycobacterium bovis- Calmette-Guerin bacillus infection in C57Bl/6 mice

Mechanisms of protective immunity to mycobacterial infection in the lung remain poorly defined. In this study, T-cell subset expansion and cytokine expression in bronchoalveolar spaces, lung parenchyma, and mediastinal lymph nodes of mice infected intratracheally with Mycobacterium bovis-Calmette-Guerin bacillus (BCG) were analyzed in parallel with histopathology and bacterial burden. M. bovis-BCG was cleared rapidly from bronchoalveolar spaces without evidence for persistence. In lung parenchyma bacteria grew during the first 4 wk followed by gradual clearance with less than 0.1% of the original inoculum persisting for more than 8 mo. Clearance of M. bovis-BCG from bronchoalveolar lavage was associated with recruitment of both neutrophils and lymphocytes. Lung CD4(+), CD8(+), and gammadelta T-cell receptor-positive T cells expanded maximally by Week 4, and declined by Week 8 to control values despite bacterial persistence. Both CD4(+) and CD8(+) lung T cells produced interferon (IFN)-gamma in response to M. bovis-BCG. Four distinct pathologic states of lung parenchymal infection were noted. Early focal sub-bronchial inflammation with transmigration of cells into airways was followed by diffuse peribronchitis, perivasculitis, and alveolitis with activated macrophages, lymphoblasts, and occasional giant cells. The latter stage corresponded to maximal M. bovis-BCG growth. Resolving infection consisted of small lymphocytes and foamy macrophages, which coincided with decreasing M. bovis-BCG colony-forming units, T-cell infiltration, and IFN-gamma expression. A final quiescent phase consisted of residual lymphoid aggregates and perivasculitis associated with persistent spontaneous IFN-gamma production. Bacterial dissemination to lymph node and spleen occurred by Week 4 and declined in parallel to lung. In contrast to lung, IFN-gamma secretion was detected only late despite early expansion of CD4(+) and CD8(+) T cells. By reverse transcriptase/polymerase chain reaction, IFN-gamma and interleukin (IL)-12 p40 messenger RNA (mRNA) in lung paralleled IFN-gamma protein production. Tumor necrosis factor-alpha, IL-4 and IL-10 mRNA expression was not increased during M. bovis-BCG lung infection. Thus, protective immunity to M. bovis-BCG in the lung evolved differently in air space, lung, and lymph node.

Neurotrophin and neurotrophin receptor expression in alveolar macrophages: an immunocytochemical study

Alveolar macrophages play a crucial role in regulating lung immune responses and in maintaining the integrity of the respiratory tract. Neurotrophins (NTs), besides to their neurotrophic activities, exhibit physiological effects in the immune system. In this study, nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), NT-3 and low- (p75) and high affinity (Trks) NT receptors were investigated by immunocytochemistry in cytospin centrifuged preparations of human alveolar macrophages. Approximately 2.5% alveolar macrophages were immunoreactive for NGF, whereas no macrophages displaying immunoreactivity for BDNF or NT-3 were observed. A 3.5% macrophages displayed immunoreactivity for TrkA-receptor protein, 10% for TrkB-receptor protein (full length isoform), and 2% for TrkC-receptor protein. No low-affinity p75 NT and TrkB[-] truncated isoform receptor immunoreactive macrophages were found. These findings support the hypothesis that NTs and the corresponding receptors may play a role in regulating immunological and functional activity of alveolar macrophages via paracrine/autocrine mechanisms.

Antigen trafficking and accessory cell function in respiratory epithelial cells

We investigated accessory cell function, antigen (Ag) trafficking, and uptake of immune complexes in isolated nasal epithelial cells (NEC) and airway epithelial cells (AEC), as well as in the two respiratory epithelial cell lines A549 and BEAS-2B. The NEC and AEC were capable of supporting Ag-specific as well as phytohemagglutinin-induced and anti-CD3 antibody-induced T-cell proliferation. We colocalized fluorescein isothiocyanate (FITC)-labeled Ags with human leukocyte antigen (HLA)-DR in A549 and BEAS-2B, utilizing laser confocal microscopy. Respiratory epithelial cells stimulated and unstimulated with interferon (IFN)-gamma were pulsed with FITC-labeled Ags for varying periods and evaluated for their ability to internalize Ag. In the unstimulated cells, intracellular punctate staining was evident at 60 min and persisted up to 120 min. In the IFN-gamma-stimulated cells (100 U/ml for 48 h), uptake occurred at 30 min, was maximal at 60 min, and diminished at 120 min. We conducted kinetic studies in the A549 and BEAS-2B cells, utilizing electron microscopy with colloidal gold-conjugated Ags (Au-OVA). At 15 min, Au-OVA was evident in the early compartments resembling the compartment of uncoupling of receptor and ligand. At 30 min, multivesicular bodies were labeled with Au-OVA, and by 60 min Au-OVA was present in the primary and secondary lysosomes. The FITC-labeled Ags colocalized with an early endosomal marker (anti-cathepsin D), a late endosomal marker (M6PR), a lysosomal marker (CD63), and with 3-(2, 4-dinitroanilino)-3'-aminomethyldipropylamine, a marker of acidic vesicles. The BEAS-2B and A549 cells, and NEC and AEC, expressed surface Fcgamma receptor and internalized IgG immune complexes. The NEC and AEC also expressed the costimulatory molecules CD80 and CD86 as determined with flow cytometry, the reverse transcription-polymerase chain reaction for RNA, and immunohistochemistry, and T-cell proliferation could be blocked by treating NEC and AEC with anti-CD80 and anti-CD86 antibodies. Our findings suggest that respiratory epithelial cells may have a role in local Ag presentation.

Proliferation of type II pneumocytes and alteration in their apical surface membrane antigenicity in pulmonary sarcoidosis

STUDY OBJECTIVE

To evaluate both the proliferation of type II pneumocytes in the alveolitis associated with pulmonary sarcoidosis and any alteration in their surface membrane antigenicity.

MATERIALS AND METHODS

We investigated 20 transbronchial lung biopsy (TBLB) specimens from 20 patients with pulmonary sarcoidosis, 7 TBLB specimens from 7 sarcoidosis patients without pulmonary involvement, and 19 normal lung specimens, using colloidal iron stain and immunostaining with anti-Thomsen-Friedenreich (TF) antigen and anti-surfactant protein-A monoclonal antibodies.

RESULTS

The density of type II pneumocytes was significantly higher in the pulmonary sarcoidosis specimens ([mean +/- SD] 11.1+/-3.7 per 1 mm alveolar septal length) than in the nonpulmonary sarcoidosis (7.8+/-1.3) or normal lung specimens (7.2+/-0.8). TF antigen was directly expressed on the apical surface of some type II pneumocytes in the pulmonary sarcoidosis specimens, but it was completely masked by sialic acids in the nonpulmonary sarcoidosis specimens and in the normal lung tissues.

CONCLUSIONS

In pulmonary sarcoidosis, type II pneumocytes proliferated and the antigenicity of the surface membrane was altered. It is suggested that these type II pneumocytes may be vulnerable to injury by natural anti-TF antibodies that are cytotoxic when present with complement. This damage may decrease alveolar surfactant and cause focal alveolar collapse proceeding to pulmonary fibrosis in some cases of pulmonary sarcoidosis.

Differential regulation of allergen-specific T(H2)- but not T(H1)-type responses by alveolar macrophages in atopic asthma

BACKGROUND AND OBJECTIVE

Previous studies have suggested that quantitative differences in TH2-type cytokine responses in the airways are of particular importance in the pathogenesis of asthma. In this study we investigated whether alveolar macrophages (AMs) and peripheral blood monocytes (PMNs) are able to significantly influence the profiles of allergen-induced TH1 (IFN-gamma) and TH2 (IL-4 and IL-5) cytokine production by CD4+ T cells in atopic asthmatic subjects versus atopic nonasthmatic subjects and nonatopic normal subjects.

METHODS

Peripheral blood CD4+ T cells were cultured alone or cocultured with either PMNs or AMs with allergen stimulation in the 3 groups.

RESULTS

Although allergen stimulation did not change TH1 or TH2 cytokine responses in cultures of CD4+ T cells alone, the addition of PMNs to the cultures induced a significant increase in production of IL-4, IL-5, and IFN-gamma (P < .01 or P < .001) in atopic asthmatic subjects and atopic nonasthmatic subjects. However, PMNs induced a significant increase for IFN-gamma (P < .05) only in normal subjects. AMs from atopic asthmatic subjects significantly enhanced production of all 3 cytokines (P < .01 or P < .001), whereas the AMs from atopic nonasthmatic subjects significantly increased only production of IL-4 (P < .01) and IFN-gamma (P < .05) but not IL-5. Furthermore, IL-4 (P = .066) and IL-5 (P < .01) production in allergen-stimulated AM-CD4+ cell cocultures was higher in atopic asthmatic subjects but significantly lower in atopic nonasthmatic subjects (P < .05) as compared with the PMN-cocultures. For IFN-gamma, no difference was found between the AM and PMN cocultures in either atopic group. Allergen-stimulated IL-5 production in coculture with both AMs and PMNs inversely correlated with both baseline FEV1 percent predicted and PD20 methacholine in atopic asthmatic subjects (P < .05, P < .01, or P < .001).

CONCLUSION

These data suggest that AMs from atopic asthmatic subjects but not atopic nonasthmatic subjects, play a significant role in airway pathogenic immunity through enhancing TH2-type cytokine production.

Alveolar macrophages from atopic asthmatics, but not atopic nonasthmatics, enhance interleukin-5 production by CD4+ T cells

Recent studies have demonstrated that different antigen-presenting cell (APC)-related factors in the microenvironment of a T cell may determine its profile and quantity of cytokine expression and production. We have therefore examined the effects of alveolar macrophages and peripheral blood monocytes on interleukin (IL)-5 production by peripheral blood CD4+ T cells from atopic people with asthma (AA), atopic people without asthma (AN), and nonatopic normal subjects (N). In response to allergen stimulation, IL-5 production was significantly enhanced by the addition of monocytes to CD4+ cell cultures in AA and AN patients (p < 0.05 and 0.01, respectively), but not in N subjects. In mitogen-stimulated CD4+ cell plus monocyte cocultures, there was a small increase in IL-5 production in all three groups (p < 0.05 for AN). In contrast, the addition of alveolar macrophages to parallel cultures significantly amplified IL-5 production only in AA patients (p < 0.05 or 0.01). Furthermore, IL-5 production by CD4+ cells in alveolar macrophage cocultures, stimulated by allergen or mitogen, was higher than that in monocyte cocultures in AA patients (p < 0.05). Conversely, in AN and N subjects, the IL-5 values for alveolar macrophage cocultures were lower than those for peripheral blood monocytes. In blocking studies, antibodies against IL-1alpha, IL-1beta, IL-6, or tumor necrosis factor-alpha differentially suppressed macrophage-enhanced IL-5 production (p < 0.05 for IL-1beta and IL-6) and expression of the activation marker CD25 (p < 0.05 for IL-1alpha and IL-6) by allergen-stimulated CD4+ cells in AA patients. These observations suggest that alveolar macrophages influence the quantity of IL-5 production by T cells in the airways and, as a consequence, the development of asthma in atopic individuals.

Effect of cardiopulmonary bypass on cytokine release and adhesion molecule expression in alveolar macrophages. Preliminary report in six cases

Although recent studies have shown that adhesion molecules on alveolar macrophages are important in a variety of pulmonary diseases, there have been few studies on the phenotypic and functional changes of alveolar macrophages during cardiopulmonary bypass. To investigate the possible role of alveolar macrophages in activating pulmonary immunity during cardiopulmonary bypass, we measured the expression of adhesion molecules on alveolar macrophages and peripheral blood monocytes in patients undergoing cardiopulmonary bypass. Antigens were stained with monoclonal antibodies against adhesion molecules, and the expression of antigens was quantified by flow cytometry as the ratio of specific to nonspecific linear fluorescence. On alveolar macrophages obtained after the release of aortic cross-clamp, macrophages as compared with alveolar macrophages obtained before cardiopulmonary bypass, there was a significant enhancement of CD11a, CD11b, CD11c, and CD18. In addition, alveolar macrophages, but not peripheral monocytes, produced higher levels of TNF-alpha and IL-8 when they were cultured in vitro. A higher expression of CD11 and CD18 on alveolar macrophages and enhanced production of cytokines after release of the aortic cross-clamp may contribute to immune activation in lung by macrophage-lymphocyte interaction.

Selective inhibition of T cell proliferation but not expression of effector function by human alveolar macrophages

BACKGROUND

Alveolar macrophages are thought to play an important part in regulating lung immune responses. While it is clear that human alveolar macrophages suppress T cell proliferation in vitro, the mechanisms by which this is achieved are not clear, nor is it known whether alveolar macrophages also inhibit other aspects of T cell function.

METHODS

Peripheral blood mononuclear cells were stimulated with phytohaemagglutinin or house dust mite allergen, and cultured with variable numbers of autologous alveolar macrophages obtained by bronchoalveolar lavage from 20 normal subjects.

RESULTS

Alveolar macrophages induced a reversible inhibition of T cell proliferation in response to both mitogen and allergen stimulation, with the latter being considerably more susceptible to inhibition. This was achieved via heterogenous mechanisms, involving both soluble factors derived from alveolar macrophages and cell-cell contact. Despite inhibiting proliferation, alveolar macrophages had little or no effect on T cell calcium flux, the characteristic changes in CD3, CD2, CD28 and interleukin-2 (IL-2) receptor expression which accompany normal T cell activation, and IL-2 and interferon gamma secretion. In contrast, alveolar macrophages inhibited the tyrosine phosphorylation of proteins which may be involved in IL-2 receptor-associated signal transduction.

CONCLUSIONS

The immunoregulatory properties of alveolar macrophages are relatively selective, allowing T cell activation and cytokine secretion while inhibiting T cell proliferation within the lung.

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

Peripheral lung tissue contains large numbers of T cells, strategically located for immune surveillance at the blood-air interface. Given the intensity of antigenic exposure at this site, it is clear that local T-cell activation events require strict control, in order to maintain tissue homeostasis. How this control is achieved in this unique tissue microenvironment is unknown, and the present study sought to elucidate the process via detailed analysis of the surface phenotypic characteristics of freshly isolated lung T cells. We report below that these cells display typical characteristic of 'postactivation', notably elevated basal Ca2+ concentrations, down-modulated T-cell receptors, expression of Ia and 'late' activation antigens and concomitant CD4/CD8. However, levels of interleukin-2 receptor and CD2 expression were below those expected of 'activated' T-cell populations, and virtually all of the cells were found to be in the G0/G1 phases of the cell cycle. These properties bear a remarkable similarity to those of T cells activated in the presence of endogenous tissue (alveolar) macrophages from the lung (see accompanying paper). We hypothesize that they reflect the in vivo operation of an endogenous macrophage-mediated T-cell anergy-induction process, the function of which is to limit the local clonal expansion of T cells in peripheral lung tissue after in situ activation.