The role of macrophages in pathogenesis of limited inflammation

It is shown on 250 male rats that a limiting capsule around an inflammation focus develops in the presence of bacteria as well as intoxication and possibility of infection generalization. Macrophages (Mph) phagocyte necrotic tissue in aceptic inflammation and stimulate reparation with formation of a scar. The role of Mph is more complicated in modeling of soft tissue abscess: they phagocyte bacteria inducing immune system involvement into the inflammatory process, stimulate primary cooperation of cells which produce inflammatory tissue mediators, regeneratory processes with final formation of a connective tissue capsule around a focus of purulent inflammation. When the system of phagocyting mononuclear cells is stimulated, all processes in the zone of inflammation become activated; when this system is inhibited the processes slow down.     

The critical role of macrophages in the pathogenesis of hidradenitis suppurativa

Introduction

Hidradenitis suppurativa (HS) is a painful chronic inflammatory disease with a prevalence between 1 and 4% of general population. The pathogenesis of HS long eluded scientists, but growing evidence suggests that it is a consequence of inflammatory dysregulation.

Findings

Recent studies suggest that dysregulated immune response to skin flora and overexpression of inflammatory cytokines leads to chronic skin inflammation seen in HS. Macrophages are the most numerous inflammatory cells found in HS infiltrates and release numerous pro-inflammatory cytokines such as IL-23, and IL-1β and TNF-α, exacerbating the inflammation and contributing to the pathogenesis of HS. Furthermore, in HS, there is dysregulated function of other immune players closely associated with macrophage function including: matrix metalloproteases (MMP) 2 and 9 overexpression, toll-like receptor upregulation, impaired Notch signalling, NLRP3 inflammasome upregulation, and dysregulated keratinocyte function. Lifestyle factors including obesity and smoking also contribute to macrophage dysfunction and correlate with HS incidence.

Conclusions

The overexpression of pro-inflammatory cytokines and subsequent efficacy of anti-cytokine biologic therapies highlights the importance of managing macrophage dysfunction. Future therapies should target key molecular drivers of macrophage dysfunction such as TLR2 and NLRP3 overexpression.

     

Reappraisal of the role of macrophages in the pathogenesis of atherosclerosis

New Zealand rabbits were fed an atherogenic diet, 8 with and 8 without twice weekly intravenous injections of GdCl2. The injections caused a reduction in the phagocytic activity of the reticuloendothelial system by one fourth to one half. No significant differences were found between the two groups in the planimetric extent of atheromata in the aortae. GdCl2 treatment inhibited the deposition of sudanophilic lipids in depth of the arterial wall. The findings indicate that macrophages are the primary foam cells and their uptake of lipoproteins is essential for the deposition of lipids in myocytes. Lipid-laden myocytes and ground substance mucopolysaccharides represent sinks in which lipids are removed from the flow and accumulate locally.     

Pulmonary alveolar macrophages in patients with sarcoidosis and hypersensitivity pneumonitis: Characterization by monoclonal antibodies

Using a panel of monoclonal antibodies (MoAbs), the frequency of cells bearing Class I and Class II major histocompatibility complex (MHC) determinants, transferrin receptor (TR) sites, and interleukin-2 receptors (IL-2R) has been evaluated on pulmonary alveolar macrophages (PAM) recovered from the bronchoalveolar lavage (BAL) fluid of 21 patients with pulmonary sarcoidosis (including 11 cases with active sarcoidosis and 10 cases with inactive disease), 8 patients with hypersensitivity pneumonitis (HP), and 6 normal non-smoking volunteers. When the frequency of Class II DR-positive cells was considered, 64.3% of control PAM expressed HLA-DR products. No statistically significant differences were observed between controls and sarcoid patients, while HP patients showed an enhanced proportion of DR⁺ PAM with respect to normal PAM (P<0.05). On the contrary, the frequency of PAM expressing HLA-DQ molecules was higher in both active sarcoidosis and HP patients with respect to patients with inactive sarcoidosis and normal subjects (P<0.001). A statistically significant increase in Class I antigen-positive PAM has been demonstrated in HP patients as compared to controls (P<0.05). Active sarcoid patients showed a higher number of PAM-bearing TR sites than controls and other groups of patients considered (P<0.001). An increase in the percentage of IL-2R-positive PAM has been demonstrated in active sarcoidosis (P<0.001). Our data suggest that (1) PAM of patients with the above-considered interstitial lung diseases are in a state of activation and exhibit structures which play a crucial role in antigenic recognition by T lymphocytes, such as HLA-DQ molecules; (2) the presence of TR in PAM of patients with active sarcoidosis could be related to a more advanced differentiation stage of these cells and/or to particular functional properties; and (3) a direct role of the IL-2/IL-2R system in the interaction between T cells and monocytes in sarcoid lung is crucial. Besides representing an additional parameter which differentiates BAL features of sarcoidosis from those of HP patients, these results could represent a useful tool in the evaluation of the macrophagic component of alveolitis by the BAL.     

The role of pulmonary intravascular macrophages in the pathogenesis of African horse sickness.

African horse sickness (AHS) is a disease of equids, characterized by severe pulmonary oedema and caused by an orbivirus. To determine the role of pulmonary intravascular macrophages (PIMs) in the development of pulmonary microvascular changes in this disease, five horses were given an intravenous inoculation of 10(6)TCID50of serotype 4 of AHS virus. Viral replication was detected in endothelial cells, PIMs, interstitial macrophages and fibroblasts. Alveolar and interstitial oedema, and changes in pulmonary microvasculature, consisting mainly of the sequestration of neutrophils and the formation of platelet aggregates and fibrinous microthrombi, were related to endothelial changes and to a high degree of PIM activation. This suggested that the PIMs, once activated, contributed to these vascular changes by releasing chemical inflammatory mediators.     

Inorganic cytoplasmic inclusions in alveolar macrophages. The role of cigarette smoking.

A case of tobacco-associated pulmonary fibrosis, with the results of histological, ultrastructural, and spectrometric analysis is reported. Abnormalities of the alveolar macrophages, which are particularly affected by tobacco inhalation were found. The size of the macrophages was increased and many large, polymorphous inclusions, including fat vacuoles and granular deposits, which were either homogeneous or electron lucent vacuoles, were seen in the cytoplasm. A few laminar structures were observed. All of these lesions are frequently found in cigarette smokers. Still more interesting was the discovery of numerous fiber-, needle-, or laminar-like inclusions that varied in size from 0.2 to more than 2 mu. The digestions of the inclusions with potassium hydroxide confirmed the presence of various metals, such as sodium, magnesium, potassium, iron, sulfur, and especially, aluminum, and silicon; these last two elements correspond to the presence of kaolinite in the tissue, as has been previously described, and can be considered as evidence of the use of tobacco.     

The role of human alveolar macrophages in the allogeneic and autologous mixed leucocyte reactions.

Human alveolar macrophages (AM) are deficient in their ability to promote antigen-stimulated lymphocyte proliferation when compared to in-vitro-aged blood derived macrophages (BM). The mechanisms behind the unique accessory cell function of human AM are unknown. The current paradigm for accessory cell function requires antigen presentation in the context of gene products of the HLA-DR locus of the major histocompatibility complex (Class II, DR antigens) and secretion of non-specific second signal (e.g. interleukin 1). While both AM and in-vitro-aged BM have limited ability to secrete interleukin 1 (IL-1), more than 90% of both cell types express DR antigens. However, only BM consistently promote antigen-stimulated lymphocyte proliferation. Addition of IL-1 does not restore accessory cell function of human AM for antigen stimulation. It is possible that DR antigen expression and/or function of AM may be more contributory for their accessory cell function. The mixed leucocyte reaction (MLR) and autologous mixed leucocyte reactions (AMLR) in which DR epitopes stimulate proliferation of allogeneic and autologous T cells, respectively, are useful in vitro assays for assessment of DR-restricted macrophage-lymphocyte interactions. In the current studies we demonstrate that AM are usually equivalent to autologous in-vitro-aged BM in their ability to stimulate an MLR, but are consistently deficient relative to such BM in their ability to stimulate an AMLR. Experiments in which the two cells were co-cultured indicate that AM-mediated suppression does not account for the limited ability of AM to stimulate an AMLR. The deficiency of AM to act as accessory cells for antigen-stimulated lymphocyte proliferation may relate to their relative inability to stimulate autoreactive T cells and be attributable to differences in DR antigen expression and/or function.     

Phenotypic and functional changes in alveolar macrophages contribute to the pathogenesis of pulmonary sarcoidosis.

Bronchoalveolar lavage (BAL) was performed on 10 patients with sarcoidosis and 10 normal volunteers. In each case aliquots of the lavage were used to prepare cytospins on which differential cell counts were performed. Immunocytological methods using monoclonal antibodies RFD1 and RFD7 (identifying dendritic cells and mature macrophages in normal tissues) were performed to identify macrophage subsets. Sarcoid BAL contained a significantly higher proportion of RFD1+ cells (mean 44.7 +/- 10.32% compared to 12.3 +/- 4.0% in normals). Much of this increase was accounted for by a highly significant rise in the proportion of cells with the double phenotype RFD1+/RFD7+ (27.2 +/- 6.1% in sarcoid compared to 7.3 +/- 2.0% in normal). Suspensions of sarcoid and normal BAL were also studied in autologous mixed lymphocyte reactions (AMLR) using peripheral blood mononuclear cells (PBM) as a responder population. AMLRs were therefore set up using BAL, PBM, and BAL with PBM. In each case reactivity was compared to mitomycin treated controls. These studies revealed that sarcoid PBM expressed markedly reduced AMLR reactivity when compared to normal but both sarcoid and normal BAL were relatively unreactive. BAL admixed with PBM suppressed peripheral blood AMLR reactivity in the normals. In sarcoid patients BAL admixed with PBM abolished AMLR completely. We suggest that changes within the BAL macrophage populations in sarcoid patients may significantly influence the pathogenesis of this disease.     

The prolonged life-span of alveolar macrophages

To further examine the half-life of alveolar macrophages, chimeric CD 45.2 mice were generated through bone marrow transplantation of donor CD 45.1 cells. Before administration of donor cells, recipient mice were divided into two cohorts: the first cohort received total body irradiation; the second cohort also received irradiation-however, the thorax, head, and upper extremities were shielded with lead. Flow cytometric analysis was then performed on blood, peritoneal, and bronchoalveolar lavage cells over time to quantify engraftment. The data generated for the unshielded cohort of mice revealed a macrophage half-life of 30 days. In the shielded cohort, however, we found that by 8 months there was negligible replacement of recipient alveolar macrophages by donor cells, despite reconstitution of the blood and peritoneum by donor bone marrow. Consistent with these findings, the mean fluorescent intensity of alveolar macrophages remained stable over a 4-week period after in vivo PKH26 dye loading. Together, these data show that previous alveolar macrophage half-life studies were confounded by the fact that they did not account for the toxic effects of irradiation conditioning regimens, and demonstrate that the bone marrow does not significantly contribute to the alveolar macrophage compartment during steady-state conditions.     

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.     

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 role of titanium in the altered endotoxin-induced nitric oxide synthase expression in alveolar macrophages from titanium-alloy-implanted rats

We have found that the concentration of titanium (Ti) in the blood of patients with loosened Ti-alloy prostheses is elevated. An increase in the levels of elemental Ti in the blood and lung tissues of rats with an alloyed-Ti implant also has been found. The cellular reaction to elevated elemental Ti in the circulation remains unclear. We further performed experiments to examine the changes of inducible nitric oxide synthase (iNOS) expression in alveolar macrophages from alloyed-Ti-implanted rats. The elevation of nitrite and iNOS expression induced by lipopolysaccharide (LPS) was suppressed. The in vitro effect of a soluble form of Ti was further investigated. Ti (0.01-0.06 mM) inhibited the LPS-induced nitrite production and iNOS expression in alveolar macrophages from normal rats without any cytotoxic effects. LPS induced protein tyrosine phosphorylation, tyrosine-phosphorylation of lyn (a CD14-receptor-associated-tyrosine kinase), and degradation of IkappaB-alpha protein (inhibitor of NF-kappaB) in alveolar macrophages. These events were inhibited by co-incubation with Ti. These results indicate that elemental Ti may impair iNOS expression in alveolar macrophages through the alteration of protein tyrosine phosphorylation and NF-kappaB activation. The inhibitory action of Ti on cellular responses of alveolar macrophages may be anti-inflammatory and thus may depress local defense mechanisms related to microbial killing.     

Interleukin-8 gene expression from human alveolar macrophages: the role of adherence

The human alveolar macrophage (AM) is an important immune effector cell of the lung, as this cell possesses potent antimicrobial activities and has the ability to present antigen. In addition, the Am can secrete a number of regulatory and chemotactic cytokines in response to both endogenous and exogenous stimuli. In this study, we demonstrate that the adherence of AM to plastic or cellular substrates is an important activation event leading to the gene expression of novel chemotactic cytokine interleukin (IL)-8. The culturing of AM on plastic induced the time-dependent accumulation of IL-8 mRNA. In addition, adherence of these cells induced the gene expression of the proinflammatory cytokines tumor necrosis factor-alpha and IL-1 beta. This adherence phenomenon was not specific to plastic, as AM cultured on collagen- or fibronectin-coated plates also expressed IL-8 mRNA upon adherence. The adherence of Am resulted in the induction of de novo IL-8 mRNA synthesis, as this mRNA accumulation was completely abrogated by actinomycin D. Adherence-induced IL-8 mRNA expression was not altered by cycloheximide, suggesting that de novo or ongoing protein synthesis was not required for induction of IL-8 message. Adherence of AM to plastic not only upregulated IL-8 mRNA levels but also induced the production of extracellular IL-8 immunoreactive protein. Both adherent and nonadherent AM treated with lipopolysaccharide generated substantial amounts of IL-8 mRNA. Adherence and lipopolysaccharide, however, acted in a synergistic fashion to dramatically augment the production of extracellular IL-8 from these cells. Our findings would suggest that AM adherence is an important macrophage-activating event that may play a critical role in the modulation of lung inflammatory responses.