Alveolar macrophages, blood monocytes, and density-fractionated alveolar macrophages differ in their ability to promote lymphocyte proliferation to mitogen and antigen

Effect of exogenous surfactant on Paediatric Bronchoalveolar lavage derived macrophages' cytokine secretion

BACKGROUND

Bronchoalveolar lavage is a useful bronchoscopy technique. However, studies in "normal" children populations are few. Furthermore, the anti-inflammatory effects of exogenous pulmonary surfactants on the bronchoalveolar cellular components are limited.

METHODS

Thirty children, aged 3 to 14 years, underwent diagnostic bronchoscopy and bronchoalveolar lavage. Differential cytology, cytokine and chemokine measurements were performed on the fluid after exogenous surfactant exposure. The aim of the study was to investigate the potential anti-inflammatory effects of exogenous surfactants on the bronchoalveolar lavage fluid, specifically alveolar macrophages of healthy South African children.

RESULTS

Alveolar macrophages were the predominant cellular population in normal children. Patients with inflammatory pneumonopathies had significantly more neutrophils. Levels of inflammatory cytokines were significantly lower after exogenous surfactant exposure. Moreover, IL-10 and IL-12 cytokine secretion increased after exogenous surfactant exposure.

CONCLUSION

This study provides the first data on bronchoalveolar lavage of healthy South African children. Bronchoalveolar lavage fluid from patients with pulmonary inflammation was characterised by neutrophilia. Finally, we propose that exogenous surfactant treatment could help alleviate inflammation in diseased states where it occurs in the tracheobronchial tree.

Evaluation of inflammatory cytokine secretion by human alveolar macrophages

The alveolar macrophage (AM) secretes interleukin 1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-8 (IL-8), all of them inflammatory cytokines involved in the pathogenesis of many lung diseases. The aim of the present work was to evaluate the basal and stimulated secretion of these cytokines by human AMs. Human AMs were collected by bronchoalveolar lavage (BAL) from four healthy controls and 13 patients with diffuse interstitial lung disease (five cases of sarcoidosis, three of hypersensitivity pneumonitis and five of idiopathic pulmonary fibrosis). AMs were cultured in the presence or absence of different concentrations of lipopolysaccharide (LPS), phorbolmyristate and gamma-interferon. IL-1beta, TNF-alpha, IL-6 and IL-8 levels were measured in BAL fluid and culture supernatant using specific enzyme-linked immunosorbent assays. The substance found to stimulate the secretion of inflammatory cytokines to the greatest extent was LPS at a concentration of 10 microg/ml. Regarding the secretion of IL-1beta, four observations were of interest: basal secretion was very low; LPS exerted a potent stimulatory effect; considerable within-group variability was observed; and there were no significant differences in the comparisons among groups. With respect to TNF-alpha secretion, the results were similar. The only striking finding was the higher basal secretion of this cytokine with respect to that of IL-1beta. Regarding the secretion of IL-6, the same pattern followed by TNF-alpha was found. However, it should be stressed that the increase induced by LPS was smaller than in the two previous cytokines. Regarding the secretion of IL-8, three findings were patent: the strong basal secretion of this cytokine; the moderate increase induced by LPS; and the existence of significant differences among the different groups with respect to the stimulated secretion of this cytokine, which reached maximum values in patients with idiopathic pulmonary fibrosis. Finally, it should be noted that the pattern of cytokines observed in the BAL fluid was similar to that found in cultured AM supernatants. The pattern of inflammatory cytokine secretion by AMs differs from that of other cells of the mononuclear phagocyte system (MPS). In this sense. AMs secrete low amounts of IL-1, moderate amounts of TNF-alpha and IL-6, and high quantities of IL-8. Adherence is an important stimulus in the secretion of these molecules and LPS elicits an increased secretion inverse to the basal secretion. There is considerable individual variability in the secretion of inflammatory cytokines by the AMs of patients with interstitial lung disease and the AMs of these patients are primed in vivo for the secretion of these cytokines. The results of our study, carried out in vitro, can be extrapolated to the in vivo setting.

Increased release of matrix metalloproteinase-9 in bronchoalveolar lavage fluid and by alveolar macrophages of asthmatics

In order to determine whether matrix metalloproteinases (MMPs) contribute to inflammation in asthma, we have examined the release of MMPs in bronchoalveolar lavage (BAL) fluids and their production and regulation by alveolar macrophages (AM), in short-term culture. BAL was collected from 38 asthmatic subjects (24 untreated and 14 treated with inhaled corticosteroids), 26 healthy nonsmokers, and 18 patients with chronic bronchitis used as a control group for another inflammation. The profile of MMPs present in BAL fluid and AM supernatant, determined by zymographic analysis, was found to be similar in all populations. The main enzyme released was identified immunologically as MMP-9, a potent collagenolytic and elastolytic enzyme. Its release, measured using enzyme immunoassay, was significantly enhanced in fluids and in AM supernatants from untreated asthmatics compared with those from the other populations. Enhanced MMP-9 levels, in asthma, could not be explained by a different sensitivity of AM to interleukin-4, interferon-gamma, or dexamethasone, compounds that have been shown to inhibit MMP-9. The phorbol ester phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, significantly increased MMP-9 in AM from healthy control subjects but not in those from untreated asthmatics. Calphostin C and H7, PKC inhibitors, significantly reduced PMA-stimulated MMP-9 release in AM from healthy control subjects and spontaneous MMP-9 release in AM from untreated asthmatics. H8, a PKA inhibitor, was inactive in both populations. These data suggest that the stimulation of MMP-9 release in AM from untreated asthmatic patients occurs, at least partly, via signals activating PKC.

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.

Mucosal immunoadjuvant activity of liposomes: role of alveolar macrophages

Previously, we have reported on a liposomal adjuvant system for stimulation of both systemic IgG and mucosal s-IgA responses against viral antigens (influenza virus subunit antigen or whole inactivated measles virus) administered intranasally to mice. Immune stimulation is observed with negatively charged, but not with zwitterionic, liposomes and is independent of a physical association of the antigen with the liposomes. Furthermore, liposome-mediated immune stimulation requires deposition of the liposomes and the antigen in the lower respiratory tract. In the present study, it is shown that alveolar macrophages (AM) are the main target cells for negatively charged liposomes administered to the lungs of mice. AM isolated from animals, to which negatively charged liposomes were administered beforehand, showed large intracellular vacuoles, suggestive of massive liposome uptake. Under ex vivo conditions, both AM and RAW 264 cells exhibited a high capacity to take up negatively charged liposomes. The deposition of negatively charged liposomes, but not zwitterionic, liposomes in the lung reduced the phagocytic and migratory behaviour of AM, as assessed on the basis of transport of carbon particles to the draining lymph nodes of the lungs. Depletion of AM in vivo with dichloromethylene diphosphonate, facilitated an enhanced systemic and local antibody response against influenza subunit antigen deposited subsequently to the lower respiratory tract. In conclusion, these data provide support for the hypothesis that uptake of negatively charged liposomes blocks the immunosuppressive activity of AM, thereby facilitating local and systemic antibody responses.

The kinetics of surface expression of CD11/CD18 integrins and CD54 on monocytes and macrophages

Cells of the macrophage lineage mediate extremely important normal functions of the immune system. Such functions are in part related to interactions between cell-bound LeuCAMs and their ligands. MoAb staining and flow cytometric analysis were used to follow changes in surface expression of LeuCAMs and the LFA-1 ligand CD54 during maturation of peripheral blood monocytes (BM) in vitro. Surface expression of these molecules increased on BM following isolation, the greatest increase being in CD54 and CD11c. Following an initial increase, there was a reduction in CD11a expression after 2 weeks in culture, this being greater on adherent compared with suspension-maintained cells. Expression of CD11b remained high throughout the culture period. LeuCAM and CD54 expression was further compared on freshly isolated alveolar macrophages (AM) and BM paired donors. A reciprocal relationship was observed between CD11c and CD11b on AM and BM, in that BM expressed higher levels of CD11b than CD11c, whilst the converse was true for AM. CD54 expression was also higher on AM than on BM, whilst there was no significant difference in expression of CD11a on these cells. These data suggest that consistent changes occur in the surface expression of the LeuCAMs and CD54 as monocytes mature into macrophages, which may reflect the specific functions of these cells.

Delineation of pulmonary alveolar macrophage subpopulations by flow cytometry in normal subjects and in patients with lung cancer

We have previously described alterations in pulmonary alveolar macrophage (PAM) function in patients with lung cancer when compared with control subjects. This study examined PAM from five patients with lung cancer, seven normal volunteers and nine control patients, to assess whether any differences in surface phenotypic markers were present in lung cancer versus non-cancer subjects, and what changes might be induced with interferon-gamma (IFN-gamma) stimulation. After 3 days' culture with or without IFN-gamma no differences were seen in the percentages of cells staining positively in each group for HLA class I, class II and ICAM-1 (CD54) antigens. However, in 13 out of 14 control subjects, and only one out of the five cancer subjects, dual PAM populations were identified. The second PAM population (PAM-2) was larger and demonstrated a higher expression of class I and ICAM-1 antigens. Unlike the unfractionated PAM population, PAM-2 consistently responded to IFN-gamma stimulation with an increase in both class I (90 +/- 25%) and ICAM-1 (45 +/- 10%) antigens, while there was no change in class II antigen expression. In three subjects PAM-2 was found to induce a significantly greater mitogen response than the rest of the PAM population. If confirmed in a larger group of patients, the absence of PAM-2 in the majority of patients with lung cancer may underlie the functional PAM defects observed in these patients.

Normal and sarcoid alveolar macrophages differ in their ability to present antigen and to cluster with autologous lymphocytes

Human bronchoalveolar macrophages from normal individuals function poorly as accessory cells for the presentation of common recall antigens. In sarcoidosis, alveolar macrophages (AM) are reported to be effective accessory cells for the presentation of such antigens. In this study normal and sarcoid AM were compared with blood monocytes for their ability to act as accessory cells in presenting tuberculin purified protein derivative (PPD) and streptokinase-streptodornase (SKSD) to autologous T lymphocytes, or to form spontaneous, antigen- or mitogen-induced clusters with the T cells. When compared to autologous monocytes, normal AM failed to present the two recall antigens effectively. Likewise normal AM formed very few clusters with T lymphocytes when compared to monocytes, even in the presence of antigens or the mitogen phytohaemagglutinin (PHA). In contrast, sarcoid AM presented both antigens as effectively, and were equally effective as monocytes in forming clusters with T lymphocytes, spontaneously and in further response to antigen or mitogen. The results suggest that in sarcoidosis enhanced accessory cell function and enhanced cluster formation may be related features of bronchoalveolar macrophage populations.

Four monoclonal antibodies, AMH-1, -2, -3, and -4, give varied reactivities with monocytes, alveolar macrophages, and epithelioid-cell granulomas

Four monoclonal antibodies, termed AMH-1, AMH-2, AMH-3, and AMH-4, raised against human lung macrophages in bronchoalveolar lavaged fluid, alveolar spaces, and interstitia of lung tissue are described. The antibodies were produced according to hybridoma technique by immunizing mice with bronchoalveolar lavaged cells. All four monoclonal antibodies reacted with macrophages in bronchoalveolar lavaged fluid and alveolar spaces by immunohistochemical staining and flow cytometric analysis, but they gave different reactivity patterns with the monocyte-macrophage lineage. AMH-1 did not react with peripheral blood monocytes, peritoneal macrophages, or pulmonary interstitial macrophages. Although AMH-2 reacted weakly with blood monocytes and with some of the pulmonary interstitial macrophages, it did not react with peritoneal macrophages. AMH-3 did not show reactivities with either blood monocytes or peritoneal macrophages but was positive for most of the pulmonary interstitial macrophages. AMH-4 was reactive with cells from the monocyte-macrophage lineage. There was a correlation between the reactivity patterns of all four antibodies to macrophages in bronchoalveolar lavaged fluid and the patients' smoking habits. Most significantly, epithelioid cells of lung granulomas obtained from patients with sarcoidosis and hypersensitivity pneumonitis were negative for AMH-1 but were strongly stained by AMH-2, AMH-3, and AMH-4. Differences among the four antibodies in their reactivities with macrophages and granulomas in lungs indicate that lung macrophages contain heterogeneous populations which are in various states of differentiation and maturation and that the epithelioid cells and lung macrophages share the same membrane antigens. Therefore, these antibodies would be useful reagents for investigating the subpopulations and functions of macrophages in lungs and for clarifying the pathogenesis of granulomatous lung diseases.

Immune aspects of sarcoidosis

Although the initiating factor(s) is unknown, it is now accepted that pulmonary sarcoidosis develops as a result of an over-stimulated local cellular immune response. Starting as a lymphocytic alveolitis, there is a progression to granuloma formation within the interstitium as stimulated T lymphocytes release mediators capable of attracting and activating monocytes to differentiate into macrophages and epithelioid cells. We are also aware that macrophage-like cells must act as antigen presenters to initiate T cell stimulation within the immune response. To date, interest in the alveolar macrophages of patients with sarcoidosis has focused more on their passive role as responders of the soluble T cell products released as the disease progresses. This paper explores the active role of mononuclear non-lymphoid cells as inducers of immune responses, by taking advantage of monoclonal antibodies capable of discriminating between phenotypically distinct subsets of macrophages. Recent results are presented that suggest a central role for these cells in controlling the course of this disease, focusing specifically on the mechanisms underlying the failure in some patients to resolve the interstitial inflammation and subsequently progressing to fibrosis. A new hypothesis proposes that aberrations in the functional capacity of macrophages may prohibit the emergence of a granuloma-resolving mechanism in some sarcoid patients.