Luminal bacterial antigen-specific CD4+ T-cell responses in HLA-B27 transgenic rats with chronic colitis are mediated by both major histocompatibility class II and HLA-B27 molecules

Rats transgenic (TG) for the human major histocompatibility complex (MHC) class I HLA-B27 and beta2-microglobulin genes develop chronic colitis under specific pathogen-free (SPF) but not sterile (germ-free, GF) conditions. We investigated the role of antigen-presenting molecules involved in generating immune responses by CD4+ mesenteric lymph node (MLN) cells from colitic HLA-B27 TG rats to commensal enteric micro-organisms. All TG MLN cells expressed HLA-B27. A higher level of MHC class II was expressed on cells from TG rats, both SPF and GF, compared to non-TG littermates. In contrast, rat MHC class I expression was lower on TG than non-TG cells. Both TG and non-TG antigen presenting cells (APC) pulsed with caecal bacterial antigens induced a marked interferon-gamma (IFN-gamma) response in TG CD4+ T lymphocytes but failed to stimulate non-TG cells. Blocking MHC class II on both TG and non-TG APC dramatically inhibited their ability to induce TG CD4+ T cells to produce IFN-gamma. Blocking HLA-B27 on TG APC similarly inhibited IFN-gamma responses. When the antibodies against MHC class II and HLA-B27 were combined, no APC-dependent IFN-gamma response was detected. These data implicate both native rat MHC class II and TG HLA-B27 in CD4+ MLN T-cell IFN-gamma responses to commensal enteric microflora in this colitis model.     

Class II MHC antigens in the rat digestive system. Normal distribution and induced expression after interferon-gamma treatment in vivo

The normal and interferon-gamma induced expression of class II MHC antigens was investigated immunohistologically in the digestive system of LEW rats. In the normal state class II molecules were present in interstitial dendritic cells, B lymphocytes and epithelial cells. Epithelial class II expression was restricted to enterocytes in certain portions of the small intestine and to some duct epithelia in salivary glands. After continuous intravenous infusion of interferon-gamma (IFN-gamma) for 3 days, class II MHC antigens were induced in large vessel endothelium and in the surface epithelia of the tongue, oesophagus and proventricle. In the gastric glands class II molecules appeared in mucous neck cells and in parietal cells, while adjacent mucous surface cells and chief cells did not acquire class II reactivity. All enterocytes, including the previously negative colonic epithelium, were induced to express class II antigens. In the salivary glands class II antigens appeared in all duct epithelia. Serous acinar cells were induced in the parotids, but in the submandibular glands and in the pancreas the serous gland epithelium stayed negative. Our study thus shows that the effects of IFN-gamma on class II MHC antigen expression in vivo depend on the differentiation pathway of the individual cell. The normal distribution in rats suggest that class II MHC antigens may play a role in peptide transport across specialized epithelia. It remains to be determined whether such a function is enhanced after IFN treatment.     

Differential expression of major histocompatibility complex class Ia, Ib, and II molecules on monocytes-derived dendritic and macrophagic cells.

Blood monocyte derived antigen presenting cells (APC) such as dendritic cells and macrophages are considered as major promising tools for antitumoral immunotherapy. In order to contribute to their phenotype characterization, we have precisely investigated their levels of expression of MHC class Ia, Ib (HLA-G) and II molecules using mainly flow cytometry quantification assays. APC were generated from monocytes cultured for 7 days in the presence of GM-CSF and IL-4 or M-CSF. These cells, which exhibited known morphological and immunological features of dendritic cells and macrophages respectively, were evidenced to display high expression of MHC class Ia and class II antigens in comparison to that found in monocytes. Dendritic cells and macrophages thus expressed 2-fold more and 4-fold more MHC class Ia molecules and 5-fold and 3-fold more MHC class II DR molecules than parental monocytes. In addition, expression of MHC class II DP and DQ molecules, not or only barely detected in monocytes, was clearly demonstrated in the two kinds of APC. In contrast, monocytes, dendritic cells and macrophages failed to express MHC class Ib HLA-G antigen. The up-regulation in monocyte-derived APC of MHC class Ia and II molecules mediating the presentation of antigen peptides to lymphocytes fully supports the interest of such APC in antitumoral immunotherapy.     

Influence of Intestinal Microflora on Murine Bone Marrow and Spleen Macrophage Precursors

To investigate the adjuvant effect of intestinal flora on macrophage–colony-stimulating factor-responsive macrophage progenitors from spleen and bone marrow, we compared progenitor numbers and phenotypic characteristics of in vitro matured macrophages in germ-free and flora-associated mice (conventional, Escherichia coli -monoassociated and conventionalized mice). The data obtained show that the flora affected differentially bone marrow and spleen progenitors. It increased the numbers of progenitors in the spleen but not in the bone marrow. It did not modify the expression of F4/80, Mac-1 and major histocompatibility complex (MHC) class II on bone-marrow-derived macrophages (BMDM), while it clearly up-regulated MHC class II expression on spleen-derived macrophages (SDM). This effect was more pronounced in flora-associated ex germ-free mice than in conventional mice and it was greatly enhanced in the absence of M-CSF. In vitro stimulation by lipopolysaccharide had no effect on marker expression of BMDM, while it decreased F4/80 and enhanced MHC class II molecules on SDM from germ-free and flora-associated mice. However, the expression of MHC class II remained lower in germ-free mice. Enhancement of MHC class II molecule expression on SDM may contribute to the protective role of flora, because successful immune responses are dependent on the expression of these molecules.     

Immune complex-FcgammaR interaction modulates monocyte/macrophage molecules involved in inflammation and immune response

The interaction between receptors for the Fc portion of IgG (FcgammaRs) from monocytes/macrophages and immune complexes (IC) triggers regulatory and effector functions. Recently, we have demonstrated that IC exert a drastic inhibition of basal and IFN-gamma-induced expression of MHC class II on human monocytes. Taking into account that the regulation of MHC class II molecules is a crucial event in the immune response, in this report we extend our previous studies analysing the effect of STAT-1 phosphorylation in the down-regulatory process, the fate of the intracellular pool of MHC class II molecules and the effect of complement on MHC class II down-regulation induced by IC. We also studied the effect of IC on the expression of MHC class II (I-A(d)) in macrophages using a mouse model of chronic inflammation. We demonstrate that IC induce a depletion not only on surface expressed but also on intracellular MHC class II content and that IC-induced down-regulation of MHC class II is not mediated by the inhibition of STAT-1 phosphorylation. On the other hand, the effect of IC is not specific for the down-regulation of MHC class II, for it could be restricted to other molecules involved in inflammatory processes. Our experiments also show that the activation of the complement system could be a crucial step on the regulation of the effect of IC on MHC class II expression. In agreement with our in vitro experiments using human monocytes, IC treatment reduces the expression of MHC class II in a mouse model of chronic inflammation.     

Immune complexes (IC) down-regulate the basal and interferon-gamma-induced expression of MHC class II on human monocytes

The interaction of Fc receptors for IgG (FcgammaRs) on monocytes/macrophages with immune complexes (IC) triggers regulatory and effector functions. Previous studies have shown that FcgammaR-IC interactions inhibit the IFN-gamma-induced expression of MHC class II in murine macrophages. However, the mechanism(s) responsible for these effects have not been elucidated. In addition, whether this IC-dependent effect also occurs in human cells is not known. Taking into account the fact that IC and IFN-gamma are frequently found in infections and autoimmune disorders, together with the crucial role MHC class II molecules play in the regulation of immune response, we explored the effect and mechanism of IC-induced MHC class II down-regulation in human peripheral blood mononuclear cells (PBMC). This effect was studied either in the presence or absence of IFN-gamma. We demonstrate that IC exert a drastic inhibition of basal and IFN-gamma-induced expression of MHC class II on human monocytes. This effect was mediated through the interaction of IC with both FcgammaRI and FcgammaRII. Moreover, similar results were obtained using supernatants from IC-treated PBMC. The IC-induced down-regulation of MHC class II is abrogated by pepstatin and phosphoramidon, supporting the role of aspartic protease(s) and metalloprotease(s) in this process. In parallel with MHC class II expression, antigen presentation was markedly inhibited in the presence of IC.     

Intrathecal application of interferon gamma. Progressive appearance of MHC antigens within the rat nervous system

Intrathecal injection of interferon-gamma induced a significant increase of the number of class I and class II major histocompatibility complex (MHC)-expressing cells within the rat nervous system. A progressive appearance of MHC-antigen-positive cells was found by light- and electron microscopic immune histology. The first level comprised cells that constitutively expressed MHC antigens in normal animals (meningeal and endoneural monocytes, some perivascular dendritic cells, and few parenchymal microglia cells, especially in the lumbar spinal cord and in the cerebellar white matter). The second level represented cells readily expressing MHC antigens after stimulation with interferon-gamma (all perivascular, dendritic cells, and microglia). The third level included ependymal cells, astrocytes, and Schwann cells. After stimulation with interferon-gamma, these neuroectodermal cells expressed MHC antigens inconsistently, usually in a low density and patchy distribution. The progressive appearance of MHC antigens may be reflected by the variances of lesional patterns found in experimental allergic encephalomyelitis of different histologic severity.     

Vitamin D differentially regulates B7.1 and B7.2 expression on human peripheral blood monocytes.

The hormonal active form of vitamin D3, 1,25-dihydroxyvitamin D3 (1, 25(OH)2D3), inhibits (through an unknown mechanism) the ability of monocytes/macrophages to induce T-cell activation. For T cells to be optimally activated, recognition of antigen/major histocompatibility complexes (MHC) by the T-cell receptor (TCR) must be accompanied by a second costimulatory signal. Considerable experimental data now suggest that this costimulatory signal is predominantly generated by B7.1 and/or B7.2 molecules, expressed on antigen-presenting cells (APC), when engaged to their counter-receptor, CD28, present on T cells. To determine whether the inhibitory effect of 1,25(OH)2D3 on monocytes/macrophages might involve modulation of the expression of B7.1 and B7.2 molecules, we analysed (by flow cytometry) the influence of 1,25(OH)2D3 and an analogue, KH 1060, on the expression of these two molecules at the surface of resting human peripheral blood monocytes. In parallel, we tested the effect of these two agents on human monocyte expression of cell-surface markers (CD14 and CD4) and antigen-presenting molecules (MHC class I and MHC class II). Our results showed that both 1,25(OH)2D3 and KH 1060 inhibited the basal expression of B7.2 in a dose- and time-dependent manner, without affecting B7.1. Moreover, these two compounds increased CD14 and reduced MHC class II and CD4 expression. Furthermore, the effect of 1,25(OH)2D3 on B7 molecule expression in combination with lipopolysaccharide (LPS) or cytokines, including interleukin-10 (IL-10), interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), was studied. The 1,25(OH)2D3-induced B7.2 down-regulation was still detectable when monocytes were activated by IL-10, IFN-gamma and TNF-alpha but not with LPS. Moreover, the induction of B7.1 by TNF-alpha was inhibited by addition of 1, 25(OH)2D3. We conclude that the ability of 1,25(OH)2D3 to decrease B7.2 expression on human monocytes might contribute to its inhibitory effect on APC-dependent T-cell activation and to its immunosuppressive properties observed in autoimmune diseases and organ transplantation.     

Local activation of nonspecific defense against a respiratory model infection by application of interferon-gamma: comparison between rat alveolar and interstitial lung macrophages

Pulmonary macrophages play a crucial role in the defense of inhaled pathogens. We characterized functional properties of alveolar (AM) and interstitial (IM) macrophages from rats. AM exhibited a pronounced microbicidal capacity as shown by an elevated production of reactive oxygen intermediates (ROI), nitric oxide (NO), tumor necrosis factor (TNF)-alpha, and tumor cytotoxicity when compared with IM. In contrast, IM were superior to AM regarding mechanisms mainly involved in the induction and maintenance of specific immune reactions (major histocompatibility complex [MHC] class II expression, interleukin [IL]-1 and IL-6). In this line, we were interested in whether the microbicidal potential of AM could be augmented by treating Lewis rats with rat recombinant interferon (IFN)-gamma (5 x 10(2) to 1 x 10(5) U/animal) intratracheally, avoiding infection of interstitial lung macrophages or other organ-associated macrophages. The pulmonary cytokine application resulted in an activation of AM when macrophages from IFN-treated animals were compared with control macrophages from saline-treated rats 18 h after the treatment: (1) mediator release (ROI, NO, TNF-alpha, IL-6), (2) tumoricidal activity; (3) dose-dependent increase of MHC class II expression. The local immunomodulation enhanced the resistance of normal and immunosuppressed rats against respiratory infections with Listeria monocytogenes. Taken together, local activation of lung macrophages is a feasible therapeutic strategy against pulmonary infections.     

Induction of MHC-determined antigens in the lung by interferon-gamma

Recombinant murine interferon-gamma (IFN-gamma) was administered in 6 to 9 daily intraperitoneal injections to B10.BR (H-2k) mice. The distribution of some selected class I and II major histocompatibility complex-determined antigens was localized by immunocytochemistry with the use of anti-H-2Kk and anti-IAk monoclonal antibodies and avidin-biotin-peroxidase in unfixed, frozen lungs for light microscopy and in fixed lungs for electron microscopy. In normal control mice no class I antigens were detected in the lung either by light microscopy or by ultrastructural immunocytochemistry. After 6 to 9 days of IFN-gamma administration, class I antigens were detectable on the endothelium of major vessels and diffusely throughout the alveolar region, presumably on alveolar capillary endothelium. Class I antigens did not withstand chemical fixation, therefore, could not be localized at the ultrastructural level. In normal, control mice class II antigens were detectable on a few interstitial macrophages, on some circulating monocytes, and on elongated cells adjacent to airways and major vessels. After 6 to 9 daily injections of IFN-gamma, larger numbers of macrophages and elongated cells, believed to be dendritic cells, were present around major airways and vessels. In addition, numerous round cells stained throughout the alveolar region. By electron microscopy these round cells included intraalveolar macrophages, although not all alveolar macrophages expressed IAk, circulating monocytes in capillary lumens, and type II pneumocytes. Type I pneumocytes had no detectable IAk. Reaction product in type II cells was limited to the basolateral membranes. Airway epithelium and endothelium remained unstained. These observations indicate that in addition to monocytes/macrophages IFN-gamma induces the expression of class II antigens on type II pneumocytes.     

Interleukin-10 differentially modulates MHC class II expression by mesangial cells and macrophages in vitro and in vivo.

Inhibition of major histocompatibility complex (MHC) class II expression by macrophages is the primary mechanism by which interleukin-10 (IL-10) exerts immune suppression. Little, however, is known of the effects of IL-10 on other types of cells which can be induced to express MHC class II during an inflammatory response. We therefore studied the effects of IL-10 treatment on the expression of MHC class II molecules in a rat model of immunologically induced glomerulonephritis. MHC class II mRNA levels in whole kidney were increased in saline-treated (control) animals with glomerulonephritis (2.6-fold increase versus normal, P = 0.028) and this was partially inhibited by treatment with IL-10 (P = NS). Double immunostaining of tissue sections was used to compare MHC class II expression by infiltrating macrophages and resident glomerular cells. IL-10 treatment reduced the proportion of glomerular macrophages which expressed detectable MHC class II (70% reduction, P = 0.03). In contrast, IL-10 treatment was associated with an increase in the number of resident glomerular cells expressing MHC class II, particularly within mesangial areas. Therefore, the effects of IL-10 on macrophages and mesangial cells were compared in vitro. IL-10 reduced constitutive MHC class II mRNA and cell surface expression by peritoneal macrophages. In contrast, IFN-gamma-stimulated mesangial cells (1097 cell line) cultured with IL-10 for 24 hr showed increased MHC class II mRNA (26% increase) and surface expression (72% increase in percentage MHC II+ by flow cytometry, P = 0.04) as compared with cells stimulated with IFN-gamma alone. IL-10 also directly up-regulated expression of ICAM-1 by 1997 cells. In conclusion, IL-10 was found to have contrasting effects on the production and cell surface expression of MHC class II molecules by mesengial cells and by macrophages, both in vitro and in vivo. The implications of these findings for IL-10-mediated immunosuppression are discussed.     

Down-regulation of MHC class II molecules and inability to up-regulate class I molecules in murine macrophages after infection with Toxoplasma gondii

Toxoplasma gondii is able to invade phagocytic cells of the monocyte-macrophage lineage and replicates within a parasitophorous vacuole. Since macrophages may activate specific T lymphocytes by presenting pathogen-derived antigens in association with molecules of the MHC, we investigated the in vitro expression of host cell molecules involved in antigen processing and presentation before and during infection of murine bone marrow-derived macrophages (BMM) with T. gondii. Fifty-one hours after addition of T. gondii tachyzoites at different parasite-to-host ratios, up-regulation of total MHC class II molecules by interferon-gamma (IFN-γ) was dose-dependently abrogated in up to 50% of macrophages compared with uninfected control cultures. Quantitative analyses by flow cytometry revealed that the IFN-γ-induced surface expression of class II antigens as well as the IFN-γ-induced up-regulation of class I molecules was significantly decreased in T. gondii-infected macrophage cultures compared with uninfected controls. However, the constitutive expression of MHC class I antigens was not altered after parasitic infection, and infected BMM remained clearly positive for these molecules. After infection of macrophages preactivated with IFN-γ for 48 h, T. gondii also actively down-regulated an already established expression of MHC class II molecules. Furthermore, kinetic analysis revealed that the reduction in intracellular and plasma membrane-bound class II molecules started ≈ 20 h after infection. While MHC class II antigens were most prominently reduced in parasite-positive host cells, culture supernatant from T. gondii-infected BMM cultures also significantly inhibited expression of these molecules in uninfected macrophages. However, down-regulation of MHC class II molecules was not mediated by an increased production of prostaglandin E₂, IL-10, transforming growth factor-beta or nitric oxide by infected BMM compared with uninfected controls. Our data indicate that intracellular T. gondii interferes with the MHC class I and class II antigen presentation pathway of murine macrophages and this may be an important strategy for evasion from the host's immune response and for intracellular survival of the parasite.     

LAG-3 (CD223) reduces macrophage and dendritic cell differentiation from monocyte precursors

Major histocompatibility complex (MHC) class II molecules expressed on monocytes may play a role in the control of differentiation of antigen-presenting cells. A soluble LAG-3 (CD223) molecule (sLAG-3) is a natural, high-affinity ligand for MHC class II. It is known to induce maturation of monocyte-derived dendritic cells in vitro and is used as a vaccine adjuvant to induce CD4 T helper type 1 responses and CD8 T-cell responses in vivo. Here, we demonstrate that sLAG-3 (but not an MHC class II-specific monoclonal antibody) reduces the differentiation of monocytes into macrophages in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) as well as their differentiation into dendritic cells in the presence of GM-CSF and interleukin-4, as shown by a decrease in CD14 and CD1a expression, respectively. Dendritic cells derived from monocytes in the presence of sLAG-3 showed impaired antigen-presentation function, as assessed by the reduced capability to induce proliferation of T cells. Our results suggest that activated LAG-3(+) lymphocytes present at sites of inflammation may reduce the differentiation of monocytes into macrophages or fully competent antigen-presenting dendritic cells, thus limiting the magnitude of the ongoing T-cell immune responses.     

MHC class II compartment, endocytosis and phagocytic activity of macrophages and putative dendritic cells isolated from normal tissues rich in synovium

The endocytic and phagocytic activities of a population of MHC IIhi CD11c+ dendritic cell (DC)-like cells in synovium-rich tissues (SRTs) of normal rat paws were compared with CD163+ cells (putative macrophages) from the same tissues and pseudo-afferent lymph DCs, peritoneal macrophages and blood monocytes. Fifty percent of CD11c+ cells and 75% of CD163+ cells isolated from SRT internalized fluorescein-conjugated dextran (FITC-DX). Of these endocytic cells, half of those expressing CD11c, but only 30% of those expressing CD163, were surface MHC class II+ (sMHC II+). CD11c+ cells were more endocytic than monocytes or pseudo-afferent lymph DC, but some CD163+ cells (type A synoviocytes) were found to be highly endocytic. CD163+ cells from SRT were more phagocytic (25%) than the general MHC class II+ population (16%). Of phagocytic cells, 40% of CD163+ cells were sMHC II(variable) and they constituted 60% of all MHC class II+ phagocytic cells. Only 18% of phagocytic MHC II+ cells expressed CD11c and the most of these were MHC IIhi. In comparison, 60% of CD163+ peritoneal macrophages were phagocytic, while blood monocytes were poorly phagocytic. Intracellular MHC class II-rich compartments (MIIC) were prominent in sMHC IIhi cells in SRT but rare in CD163+ cells. Most MHC IIhi CD11c+ cells did not have a detectable MIIC.     

Inhibition of MHC class II gene expression in uveal melanoma cells is due to methylation of the CIITA gene or an upstream activator

Most cells with an intact interferon-gamma receptor and signaling pathway are able to express MHC class II molecules when treated with cytokines such as interferon-gamma and tumor necrosis factor-a. Interestingly, primary uveal melanocytes and most ocular melanoma cells are resistant to interferon-gamma mediated induction of class II MHC genes. This unusual phenotype is hypothesized to be germane to the immune-privileged status to the eye. Via a series of experiments, we have probed the molecular basis of this class II MHC resistant phenotype. We have analyzed the methylation status of the gene encoding the class II transactivator (CIITA), and asked whether treatment of class II MHC resistant ocular melanoma cells with the demethylating agent 5'-azacytidine can restore interferon-gamma inducibility of these class II MHC genes in these cells. The data obtained suggest that the specific blockade in cytokine-induced class II MHC gene expression is due to a suppression of the gene encoding the class II transactivator (CIITA). Treatment with 5' azacytidine restores the ability of these cells to express class II MHC genes upon interferon-gamma treatment. Whilst this is reminiscent of what occurs in another immune-privileged tissue--the placental trophoblast--we show here that silencing of the CIITA gene in uveal melanocytes either involves methylation of distinct nucleotides from those detected in trophoblasts, or involves an upstream activator of CIITA gene expression.     

Monoclonal antibodies detect monocyte/macrophage activation and differentiation antigens and identify functionally distinct subpopulations of human rheumatoid synovial tissue macrophages

Monoclonal antibodies (MAbs) to functionally heterogeneous populations of human rheumatoid arthritis (RA) synovial tissue macrophages and lipopolysaccharide (LPS)-activated U937 cells were generated. These MAbs were used to characterize macrophages in situ in the synovial pannus and to study relative antigen expression on the surface of cells isolated from the synovium and from normal peripheral blood. Monoclonal antibody 3D8, an anti-CD13 MAb, reacts with an antigen expressed on the surface of blood monocytes and is a monocyte activation-related antigen that is upregulated by exposure of monocytes to interferon-gamma (IFN-gamma) and LPS. The expression of the 3D8 antigen increases in parallel with MHC class II antigen expression and also is upregulated in culture as monocytes mature to macrophages. 3D8 antigen is expressed strongly on RA synovial tissue lining cells, which are thought to be composed of macrophages. 8D7 antigen expression, detected by MAb 8D7, increases on blood monocytes on cellular activation with LPS and interferon-gamma, but in contrast to the 3D8 antigen, does not increase with monocyte maturation in vitro. The 8D7 antigen is expressed differentially on density-defined macrophage subpopulations isolated from RA synovial tissue and is expressed more strongly on macrophages that are nonangiogenic than those that are angiogenic.     

Class II antigens of the major histocompatibility complex are increased in lungs of bleomycin-treated rats.

The expression of class II molecules (Ia) of the major histocompatibility complex by isolated alveolar macrophages (AM) and alveolar type II cells from the lungs of rats with bleomycin-induced pulmonary fibrosis was examined. The percentage of Ia-positive AM and type II cells from rats treated with bleomycin as detected by flow cytometry was increased three times and two times, respectively, over the values obtained from control rats. The relative density of Ia expression, determined with a radioimmunoassay technique, showed a 50% increase in Ia density on AM and a 35% increase on type II cells. Recombinant interferon-gamma increased the expression of Ia on type II cells in vitro by 35% to the level obtained on type II cells in bleomycin-induced lung disease. We conclude that the increase of Ia expression on cells of the immune system and on pulmonary epithelial cells may have an important role in the initiation and/or amplification of inflammatory reactions in the lung and may contribute to the development of pulmonary fibrosis.     

Immunohistochemical examination of plexiform-like complex vascular lesions in the lungs of broiler chickens selected for susceptibility to idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a disease of unknown cause that is characterized by elevated pulmonary arterial pressure and pulmonary vascular resistance, and by extensive vascular remodelling. In human IPAH patients, remodelling of the pulmonary vasculature results in the formation of plexiform lesions in the terminal pulmonary arterioles. Various molecules are expressed in the human plexiform lesions, including alpha smooth muscle actin, von Willebrand factor, vascular endothelial growth factor, vascular endothelial growth factor receptor type 2, hypoxia inducible factor-1α, survivin, tenascin, collagen, fibronectin, and various immune/inflammatory cells such as, cytotoxic lymphocytes, B lymphocytes, MHC class II cells, and monocytes/macrophages are also present. Plexiform lesions rarely develop in the lungs of laboratory animals, but plexiform-like complex vascular lesions (CVL) do develop spontaneously in the lungs of broiler chickens from an IPAH-susceptible line. To examine angioproliferative and immune-system-related activities associated with CVL in broiler lungs, paraformaldehyde-fixed, paraffin-embedded lung sections from 8-week-old to 24-week-old broiler chickens were stained immunohistochemically using monoclonal or polyclonal antibodies specific for angioproliferative molecules and immune/inflammatory cells. The CVL in the lungs of broiler chickens exhibited positive staining for both angioproliferative molecules and immune/inflammatory cells. These observations combined with the close histological resemblance of broiler CVL to the plexiform lesions of human IPAH patients further validates chickens from our IPAH-susceptible line as an excellent animal model of spontaneous plexogenic arteriopathy.     

Apoptotic cells selectively suppress the Th1 cytokine interferon γ in stimulated human peripheral blood mononuclear cells and shift the Th1/Th2 balance towards Th2

Apoptotic cells are readily recognized and engulfed by phagocytes and usually do not induce inflammation or tissue damage. Furthermore, they can actively suppress a pro-inflammatory response in phagocytes: In the presence of apoptotic cells, activated monocytes/macrophages produce more of the anti-inflammatory and immunoregulatory cytokines IL-10 and TGF-β, but less of the pro-inflammatory cytokines TNFα, IL-1β and IL-12. This immunoregulatory effect is most likely mediated by several receptors on monocytes/macrophages including the thrombospondin receptor (CD36). In addition to the modulation of cytokine secretion, apoptotic cell material inhibited the expression of MHC class II molecules on the surface of monocytes/macrophages. Decreased MHC II expression appeared to be mediated predominantly by increased IL-10 secretion in a para-/autocrine manner. Here, we show that the functional modulation of antigen-presenting monocytes/macrophages by apoptotic cells also influences T cell activation and function. When human peripheral blood mononuclear cells were stimulated with recall antigens in the presence of apoptotic cells, interferonγ (IFNγ) secretion was markedly suppressed, whereas secretion of the Th2 cytokine IL-4 was not significantly altered. Hence, apoptotic cells shift the T cell cytokine secretion pattern towards a Th2-like response. This Th2 shift can largely be prevented by neutralizing IL-10, indicating an important role of this cytokine for modulating T cell cytokine secretion patterns.