Role of CD40 Ligand in Mycobacterium avium Infection

Mycobacterium avium is a common opportunistic pathogen in immunocompromised patients such as those infected with human immunodeficiency virus. Although M. avium is an intracellular organism replicating predominantly in macrophages, disseminated M. avium infection is seen in AIDS patients with CD4(+) cell counts of <50 cells/microliters, suggesting a possible involvement of a T cell-macrophage interaction for the elimination of M. avium. To determine whether CD40-CD40 ligand (CD40L) interactions play a role in M. avium infection, we studied the ability of CD40L to restrict M. avium replication in human monocyte-derived macrophages (MDM) in vitro. MDM were infected with M. avium and cocultured with CD40L-transfected 293 cells for 7 days. Intracellular growth of M. avium in these MDM was assessed by colony counting. CD40L-expressing cells inhibited growth of M. avium in MDM by 86.5% +/- 4.2% compared to MDM cultured with control cells. These findings were verified by assays using purified, soluble recombinant human CD40L (CD40LT). CD40LT (5 micrograms/ml) inhibited intracellular growth of M. avium by 76.9% +/- 18.0% compared to cells treated with medium alone. Inhibition by CD40LT was reduced by monoclonal antibodies (MAbs) against CD40 and CD40L. The inhibitory effect of CD40LT was not accompanied by enhancement of interleukin-12 (IL-12) production by M. avium-infected MDM, while CD40L-expressing cells stimulated IL-12 production by these cells. Treatment of M. avium-infected mice with MAb against murine CD40L resulted in recovery of larger numbers of organisms (0.8 to 1.0 log) from the spleens, livers, and lungs of these animals compared to infected mice which received normal immunoglobulin G. These results indicate that CD40-CD40L signaling may be an important step in host immune response against M. avium infection.     

Characteristics of Invasive Candidiasis in Gamma Interferon- and Interleukin-4-Deficient Mice: Role of Macrophages in Host Defense against Candida albicans

Murine models of invasive candidiasis were used to study the in vivo importance of gamma interferon (IFN-γ) and interleukin-4 (IL-4) in host defense against Candida albicans and to characterize the tissue inflammatory reactions, with special reference to macrophages (Mφ). Knockout (KO) IFN-γ-deficient (GKO) and IL-4-deficient (IL-4 KO) and C57BL/6 parental mouse strains were challenged intraperitoneally with 10⁸ C. albicans blastoconidia. Survival of GKO mice was significantly lower (16.7%) than that of C57BL/6 control (55.5%) and IL-4 KO (61.1%) animals, but was not correlated with the extent of organ colonization. Immunohistological analysis with a panel of myeloid and lymphoid markers revealed multiple renal abscesses, myocarditis, hepatitis, meningoencephalitis, and pneumonia in each strain, with a dominant presence of Mφ. In the absence of IFN-γ, C. albicans induced striking changes in the phenotype of alveolar Mφ and extensive perivascular lymphoid infiltrates in the lung. Impairment in nitric oxide production by peritoneal Mφ was shown only in GKO mice, and they produced Candida-specific immunoglobulin G (IgG), IgM, IgA, and IgG subclasses in lower titers. Our in vivo studies with KO mice elucidate a critical role for IFN-γ, but not IL-4, in host defense against C. albicans.Candida albicans is a common commensal organism in humans, and its importance as an opportunistic pathogen, particularly in immunocompromised patients, has continued to increase over the last two decades. According to the National Nosocomial Infections Surveillance System, the ratio of C. albicans isolates among nosocomial fungal infections increased from 52% to 63% in the 1980s (4). Phagocytic cell defects generally predispose to disseminated candidiasis; candidemia was calculated to result in 38% excess mortality and extend hospitalization by approximately 30 days (40). Besides the efforts to develop more effective and safer antifungal agents, a new therapeutic approach to augment the antifungal capacity of the host’s immune system should be investigated.The mechanisms of host defense and pathogenesis of candidiasis are not completely understood. Optimal phagocytosis of C. albicans requires opsonization; however, unopsonized yeast can be internalized by macrophages (Mφ) through the mannose receptor (21). Efficient killing of C. albicans by mononuclear phagocytes requires respiratory burst-associated toxic compounds (22), and recent data suggest that nitric oxide (NO) may also be involved in anticandidal functions of Mφ (5). Experimental evidence suggests that mononuclear phagocytes could play an important role in eradication of this pathogen, and their anticandidal activity can be augmented in vitro with granulocyte-Mφ and Mφ colony-stimulating factors and cytokines (no significant change could be measured in the level of specific immunoglobulin A [IgA] in serum or among the levels of interleukin-3 [IL-3] and gamma interferon [IFN-γ]) in both human and murine systems (23, 25, 28, 39).The in vivo benefit of cytokine treatment in disseminated candidiasis has not been established, and data from different murine models are controversial. Administration of IFN-γ has been reported to be associated with improved survival of mice after lethal challenge with C. albicans, which correlated with the anticandidal activity of peritoneal Mφ (28); another study showed a reduction in tissue fungal burden in IFN-γ-treated mice (19). However, in a different murine model, in vivo administration of IFN-γ resulted in increased susceptibility and organ colonization of four infected inbred strains (13). In vivo administration of IL-12, which has been reported to prime naive T cells for high IFN-γ expression and skew cytokine production toward a Th1-type response (38), did not modify the course of systemic candidiasis (32). In contrast, Th2-type cytokines IL-4 and IL-10 have been reported to exacerbate infection, and neutralization of IL-4 by specific antibody or soluble IL-4 receptor resulted in an enhanced production of Th1 cytokines, associated with increased resistance to systemic murine candidiasis (26, 30, 37). The controversial results of in vivo cytokine treatment may be the consequence of genetic differences among the infected strains and also the variation in protocols; the kinetics of cytokine production are influenced by several host and pathogen factors, and the effect of exogenous cytokine might depend on the condition of the infected host and stage of infection.Cytokine and receptor gene disruption strategies make it possible to examine the role of cytokines in host response to different pathogens directly. Recent studies showed an increased susceptibility of IFN-γ–receptor knockout (KO) mice to Mycobacterium bovis or Mycobacterium tuberculosis, but not to Schistosoma mansoni (1, 7, 8). Another study reported that disruption of the IFN-γ receptor gene was associated with higher susceptibility to Leishmania major and that IL-4 deficiency resulted in increased resistance, but only in certain inbred strains (17).Our study was undertaken to investigate the in vivo role of IFN-γ and IL-4 in disseminated C. albicans infection and characterize the tissue inflammatory cells by immunohistochemistry and by functional assays ex vivo. We demonstrate that IFN-γ, but not IL-4, is essential for survival in invasive candidiasis and show the dominant participation of Mφ in the inflammatory lesions of different tissues in KO as well as wild-type mice. In the absence of IFN-γ, a striking local immune regulatory alteration was observed in the lungs.     

Interferon-α mRNA in Splenic CD11b+ Marginal Zone Macrophages of C4-Deficient Mice

The absence of early complement components (C1, C4 and C2 but not C3) is a predisposing factor for systemic lupus erythematosus (SLE). Recently, we demonstrated that, in C4‐deficient (C4 def.) mice, IgM‐containing immune complexes (IgM‐IC) are filtered by the splenic barrier of marginal zone macrophages (MZM), resulting in an increased immune response against antigens within these IgM‐IC, but this could not be observed in wildtype or C3 def. mice. We hypothesized that splenic CD11b⁺ MZM play an important role in the induction of autoimmunity, and we therefore analysed their cytokine profile after isolation with the help of magnetic antibody cell sorting. mRNA was isolated, and real‐time PCR was performed with specific primers for murine IFN‐γ (IFN‐γ), interleukin‐12 (IL‐12) and IFN‐α (IFN‐α). We observe a moderate increase of IL‐12 and IFN‐γ mRNA in CD11b⁺ cells of C4 def. mice compared to wildtype cells. Surprisingly, the concentration of IFN‐α mRNA is six times higher in C4 def. mice. Preliminary results suggest that mRNA in CD11b⁺ cells of C3 def. mice is even lower than that in wt. Six hours following i.v. application of 20 µg of a murine monoclonal IgM anti‐dsDNA antibody, production of IL‐12, IFN‐γ and IFN‐α mRNA is increased in CD11b⁺ cells of both C4 def. and wt mice. Several references described increased levels of INF‐α in patients with SLE. Dendritic cells are discussed as a major source of IFN‐α. Our observation that C4‐deficient, SLE‐susceptible mice demonstrate an increased spontaneous IFN‐α production by splenic CD11b⁺ marginal zone macrophages could be an early sign and a trigger for the development of SLE. This is supported by the fact that the absence of C3 is not a predisposing factor for SLE and our observation that C3 def. animals display low levels of IFN‐α mRNA.     

In Vivo Production of Cytokines by Bone Marrow Stromal Cells and Macrophages from Patients with Myelodysplastic Syndrome

We studied functional disturbances in hemopoietic microenvironment and cytokine production by stromal sublayer in long-term bone marrow cultures and peripheral blood macrophages from patients with various forms of myelodysplastic syndrome. Production of factors stimulating the growth of normal erythroid and granulocytic precursors by cells of the stromal sublayer from patients with refractory sideroblast anemia and refractory anemia with excess blasts is impaired compared to cells from healthy donors. The medium conditioned by macrophages from patients with chronic myelomonocytic leukemia displayed a higher ability to stimulate the growth of granulocytes and macrophages compared to media conditioned by cells from donors and patients with refractory sideroblast anemia and refractory anemia with excess blasts. Cultured stromal cells and macrophages produced tumor necrosis factor- and interleukin-6. Their content in media conditioned by cells from patients with myelodysplastic syndrome surpassed that in healthy donors. Our results suggest that production of cytokines by stromal microenvironmental cells is impaired in patients with various forms of myelodysplastic syndrome.     

Upregulation of p75 Tumor Necrosis Factor Alpha Receptor in Mycobacterium avium-Infected Mice: Evidence for a Functional Role

The bacterial growth and the production of tumor necrosis factor alpha (TNF-alpha) and TNF receptors (TNF-Rs) in the spleen and blood of BALB/c mice challenged with Mycobacterium avium complex (MAC) were monitored. Infection developed in two phases: the first, up to day 21, was associated with rapid MAC multiplication in the spleen and a drop in the mycobacteremia, and the second was associated with control of the infection in both compartments. In the spleen, TNF-alpha and TNF-RII mRNA levels peaked on day 21 and then slowly decreased; however, no increase in the level of TNF-RI mRNA was observed throughout these experiments. The level of circulating soluble TNF-RII (sTNF-RII) was transiently increased after day 21. In a model in which overproduction of bioactive TNF-alpha was triggered in response to a second infection with MAC, an increased production of sTNF-RII by cultured splenocytes was also observed. Administration of an antagonist anti-TNF-RII monoclonal antibody (MAb 6G1) to infected mice inhibited the bacterial growth in the spleen, suggesting that the TNF-RII and/or sTNF-RII was functionally involved in the mechanisms that control the infection. Overall, these observations suggest that upregulation of TNF-RII or sTNF-RII contributes to modulation of the TNF-alpha antibacterial activity in MAC infections.     

Identification of Mycobacterium avium subsp. paratuberculosis in Biopsy Specimens from Patients with Crohn''s Disease Identified by In Situ Hybridization

Crohn's disease is a chronic inflammatory disease of the gastrointestinal tract of unknown etiology. We report on the presence of cell wall-deficient Mycobacterium avium subsp. paratuberculosis in 35 of 48 paraffin-embedded tissue specimens from 33 patients with Crohn's disease by in situ hybridization with IS900 as a probe.     

Prevention of UV-Induced Skin Damages by 11,14,17-Eicosatrienoic Acid in Hairless Mice In Vivo

Polyunsaturated fatty acids (PUFAs) are known to play important roles in various physiological and pathological processes. Recent studies have shown that some omega-3 (ω-3) PUFAs, such as eicosapentaenoic acid (EPA) and dodecahexaenoic acid (DHA), have protective effects on acute and chronic UV-induced changes. However, the effects of other ω-3 PUFAs including 11,14,17-eicosatrienoic acid (20:3) (ETA) on UV-induced skin damages are poorly understood. In this study, we investigated the cutaneous photoprotective effects of ETA in hairless mice in vivo. Female HR-1 hairless mice were topically treated with vehicle (ethanol:polyethylene glycol=30:70) only, 0.1% ETA, or 1% ETA once a day for 3 successive days after one time UV irradiation (200 mJ/cm²) on dorsal skins. Skin biopsy was carried out on the fourth day (72 hr after UV irradiation). We found that topical treatment with ETA attenuated UV-induced epidermal and dermal thickness and infiltration of inflammatory cells, and impairment of skin barrier function. In addition, ETA suppressed the expression of IL-1β, COX-2, and MMP-13 induced by UV irradiation. Our results show that the topical application of ETA protects against UV-induced skin damage in hairless mice and suggest that ETA can be a potential agent for preventing and/or treating UV-induced inflammation and photoaging.     

Role of γδ T Cells in Immunopathology of Pulmonary Mycobacterium avium Infection in Mice

Several studies have shown that γδ T cells influence granuloma development after infection with intracellular pathogens. The role of γδ T cells in controlling the influx of inflammatory cells into the lung after Mycobacterium avium infection was therefore examined with gene-disrupted mice (K/O). The mice were infected with either M. avium 724, a progressively replicating highly virulent strain of M. avium, or with M. avium 2-151 SmT, a virulent strain that induces a chronic infection. γδ-K/O mice infected with M. avium 2-151 SmT showed early enhanced bacterial growth within the lung compared to the wild-type mice, although granuloma formation was similar in both strains. γδ-K/O mice infected with M. avium 724 showed identical bacterial growth within the lung compared to the wild-type mice, but they developed more-compact lymphocytic granulomas and did not show the extensive neutrophil influx and widespread tissue necrosis seen in wild-type mice. These data support the hypothesis that isolates of M. avium that induce protective T-cell-specific immunity are largely unaffected by the absence of γδ T cells. Whereas with bacterial strains that induce poor protective immunity, the absence of γδ T cells led to significant reductions in both the influx of neutrophils and tissue damage within the lungs of infected mice.     

C5 Does Not Play a Major Role in the Immune Response of Mice to SRBC In Vivo

The role of complement component C5 in the immune response of mice to sheep red blood cells (SRBC) was investigated. Congenic C5-sufficient and C5-deficient B10. D2 mice and genetically C5-deficient DBA/2 mice, as such or supplemented with C5-sufficient serum, were used as experimental animals. C5-substitution of the C5-deficient mice resulted in measurable C5 levels for days. The functional half-life of C5 in C5-deficient DBA/2 mice was about 21 h. No significant differences between the IgM-responses of C5-bearing and naive C5-deficient animals were observed. This suggests that C5 does not play a major role in the primary humoral immune response of mice in vivo, although C5 seems to do so in in vitro experiments, even with the same antigen. Antigen-induced C5-production by C5-deficient mice as one of the explanations of the in vitro/in vivo discrepancy could not be confirmed experimentally.     

Distribution of IS901 in strains of Mycobacterium avium complex from swine by using IS901-detecting primers that discriminate between M. avium and Mycobacterium intracellulare.

The presence of the mycobacterial insertion sequence IS901 was studied by PCR with reference strains of Mycobacterium avium complex; 122 veterinary strains of mycobacteria, mainly M. avium complex, isolated from swine; and 15 clinical strains. Four kinds of DNA extraction methods for PCR were compared. Use of the commercial extraction matrix allowed for the faster and easier preparation of PCR-amplifiable DNA than use of NaOH heating extraction or sodium dodecyl sulfate extraction of pretreated mycobacteria. It also provided more effective protection than boiling extraction against the destruction of DNA. Four reference strains of serovars 1 to 3 possessed IS901. Nine reference strains of serovars 1, 4 to 6, 8 to 11, and 21 possessed only IS901 insertion sites. A novel PCR product was found in the other reference strains of serovars 7, 12 to 17, 19, and 20 and two clinical strains of serovar 15. It is suggested that the primers that amplified the insertion portion of IS901 divided the M. avium complex into M. avium, Mycobacterium intracellulare, and other mycobacteria. None of the 110 strains of M. avium complex isolated from swine possessed IS901. It is suggested that the absence of IS901 might be characteristic of swine-derived strains of M. avium complex.     

Role of CD4+CD25+ Regulatory T Cells in Melatonin‐Mediated Inhibition of Murine Gastric Cancer Cell Growth In Vivo and In Vitro

Melatonin is an important immune modulator with antitumor functions, and increased CD4⁺CD25⁺ regulatory T cells (Tregs) have been observed in tumor tissues of patients and animal models with gastric cancer. However, the relationship between melatonin and Tregs remains unclear. To explore this potential connection, we performed an in vivo study by inoculating the murine foregastric carcinoma (MFC) cell line in mice and then treated them with different doses of melatonin (0, 25, 50, and 100 mg/kg, i.p.) for 1 week. The results showed that melatonin could reduce the tumor tissue and decrease Tregs numbers and Forkhead box p3 (Foxp3) expression in the tumor tissue. An in vitro study was also performed to test the effects of purified Tregs on melatonin‐mediated inhibition of MFC cells. The cell cultures were divided into three groups: 1) MFC+ Tregs; 2) MFC only; and 3) MFC+CD4⁺CD25^? T cells. After treatment with different concentrations of melatonin (0, 2, 4, 6, 8, and 10 mM) for 24 h, a dose‐dependent apoptosis and cell cycle arrest at the G2/M phase was detected in melatonin‐treated MFC at melatonin concentration higher than 4 mM. There were no significant differences in the rates of apoptosis and cell cycle distributions of MFC among the three groups. In conclusion, the antigastric cancer effect of melatonin is associated with downregulation of CD4⁺CD25⁺ Tregs and its Foxp3 expression in the tumor tissue. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Apoptosis of Renal Cortical Cells in the Hemolytic-Uremic Syndrome: In Vivo and In Vitro Studies

This study examined apoptotic cell death associated with Shiga-like toxin (Stx)-producing Escherichia coli. Renal cortices from three children with postenteropathic hemolytic-uremic syndrome (HUS) and from mice infected with E. coli O157:H7 and pediatric renal tubular epithelial cells stimulated with Stx and E. coli O157:H7 extracts were examined for apoptotic changes. Apoptotic cells were detected by terminal dUTP nick end labeling of tubuli and glomeruli from HUS patients and from mice inoculated with Stx-2-positive and Stx-negative strains. Apoptosis was more extensive and severe ultramorphological nuclear and cytoplasmic changes were seen in the Stx-2-positive group. Stx caused DNA fragmentation and ultramorphological changes indicating apoptosis in cultured pediatric tubular cells. DNA fragmentation increased when cells were prestimulated with tumor necrosis factor alpha. Polymyxin extracts from Stx-2-positive and Stx-negative strains induced DNA fragmentation, but only extracts from Stx-2-positive strains caused ultramorphological changes and extensive DNA fragmentation. The results indicate that HUS is accompanied by increased apoptosis of kidney cells and that bacterial factors, possibly together with host cytokines in vivo, may activate apoptotic tissue injury.     

PCR-hybridization assay for Mycobacterium avium complex: optimization of detection in peripheral blood from humans

We evaluated the sensitivity of a DNA amplification test for the detection of Mycobacterium avium in blood samples using different blood components and different DNA extraction methods. M. avium-inoculated blood samples were processed to obtain separate blood components: peripheral blood mononuclear cells (PBMCs), polymorphonuclear cells (PMNCs), and whole-blood sodium dodecyl sulfate (SDS)-lysate pellets. The sensitivity for the detection of the lowest mycobacterial load (1 CFU/ml) was significantly greater (P < 0.01) with DNA extracted from SDS-lysate pellets than with DNA extracted from PBMCs or PMNCs. Subsequently, DNA extraction methods based on guanidine NaOH, and proteinase were compared. The sensitivity of the guanidine-based method was significantly greater (P < 0.01) than those of the others.     

Genetic Resistance of Mice to Persistent Infection with Mycobacterium Lepraemurium in Vitro: Association with Macroprage Bactericidal Responsiveness to Lymphokines and Dissociation from Production of Hydrogen Peroxide by Macrophages

Peritoneal and splenic adherent macrophages (SAC) from M. lepraemurium susceptible (C3H/HeJ) and resistant (C57B1/6J) mice were studied for their abilities to generate H₂O₂ in vitro. Unexpectedly, SAC from the susceptible C3H/HeJ strain produced more H₂O₂ than hose of the resistant C57BL/6J. In vivo sensitization with M. bovis (BCG), or C. parvum increased production of H₂O₂ by SAC from both strains, whereas in vivo sensitization with M. leraemurium enhanced H₂O₂ production only in the C3H/HeJ susceptible strains. In vitro addition of a crude lymphokine enhanced H₂O₂ production by C3H/HeJ SAC more than by C57BL/6J SAC. In vitro addition of M. lepraemurium caused an inhibition of H₂O₂ production by SAC from both strains but the inhibition was greater for the resistant C57BL/6J strain. M. leraemurium phagocytosed in vitro by untreated peritoneal macropbages of both mouse strains were morphologically altered to the aame extent. However, the addition of lymphokine dramatically increased the degree of bacterial lysis in only the C57BL/6J strain. These results, support the view that H₂O₂ plays a limited. if any, role in the protection of the host from M. lepraemurium and may even contribute to susceptibility by inhibiting the host's immune response.     

Typing of Clinical Mycobacterium avium Complex Strains Cultured during a 2-Year Period in Denmark by Using IS1245

In the present study restriction fragment length polymorphism analyses with the recently described insertion sequence IS1245 as a probe was performed with clinical Mycobacterium avium complex strains cultured in Denmark during a 2-year period. The overall aim of the study was to disclose potential routes of transmission of these microorganisms. As a first step, the genetic diversity among isolates from AIDS patients and non-human immunodeficiency virus (HIV)-infected patients was described. In addition, a number of isolates from nonhuman sources cultured during the same period were analyzed and compared to the human isolates. A total of 203 isolates from AIDS patients (n = 90), non-HIV-infected patients (n = 91), and nonhuman sources (n = 22) were analyzed. The presence of IS1245 was restricted to Mycobacterium avium subsp. avium isolates. The majority of human isolates had large numbers of IS1245 copies, while nonhuman isolates could be divided into a high-copy-number group and a low-copy-number group. Groups of identical strains were found to be geographically widespread, comprising strains from AIDS patients as well as strains from non-HIV-infected patients. Samples of peat (to be used as potting soil) and veterinary samples were found to contain viable M. avium isolates belonging to genotypes also found in humans.     

In Vivo and In Vitro Models of Demyelinating Disease: Endogenous Factors Influencing Demyelinating Disease Caused by Mouse Hepatitis Virus in Rats and Mice

Intracerebral inoculation of JHM virus (JHMV), the neuropathic strain of mouse hepatitis virus, into Wistar Furth, Wistar Lewis, and Fischer 344 rats at various ages indicated that Wistar Furth rats are more susceptible to the virus than are the other strains. Fischer 344 and Wistar Lewis rats were more resistant to inoculation at 2 and 5 days of age and completely resistant by 10 days of age. In contrast, Wistar Furth rats which were very susceptible at both 2 and 5 days of age remained susceptible until 21 days of age. Intracerebral challenge of an F1 cross between Wistar Furth and Wistar Lewis rats at 10 days of age indicated that resistance to JHMV infection is dominant. Cyclophosphamide treatment 28 days after intracerebral inoculation exacerbated an inapparent infection, leading to paralysis in eight of nine and death in six of nine Wistar Furth test rats. In such immunosuppressed animals, grey- and white-matter lesions were noted throughout the central nervous system, in contrast to the purely demyelinating lesions noted previously. Since rats, unlike mice, were not susceptible to disease after intracerebral injection with the serorelated viscerotropic strain MHV-3, we wished to extend our understanding of the neurological disease process elicited by the two viruses in rodents. For this reason, various mouse strains, including some with recognized immunodeficiencies, were challenged by different routes of inoculation. Intraperitoneal infection of nude and beige mice with JHMV indicated that lack of natural killer cell functions does not markedly enhance the susceptibility to virus, whereas T-cell activity appears to be essential for resisting infection. JHMV and MHV-3 replication in peritoneal macrophages from highly resistant A/J mice was reduced in comparison with that noted in macrophages from susceptible C57BL6/J mice. An initial intraperitoneal inoculation of JHMV was able to protect C57BL6/J mice against fatal intracerebral challenge within 3 days, whereas A/J mice remained susceptible beyond day 3. The protective effect did not appear to result from increased levels of circulating interferon, preceded elevation in serum JHMV-neutralizing antibody titers, and persisted for at least several weeks after intraperitoneal inoculation. Based on the combined studies described here and on previous work by us and others, it appears that the factors influencing the outcome of coronavirus disease in rodents are age at inoculation, route of challenge, genetic constitution of the virus and host, and competence of the immune system, particularly cellular immunity involving T-cells.     

Interleukin-4 Regulates the Expression of CD209 and Subsequent Uptake of Mycobacterium leprae by Schwann Cells in Human Leprosy

The ability of microbial pathogens to target specific cell types is a key aspect of the pathogenesis of infectious disease. Mycobacterium leprae, by infecting Schwann cells, contributes to nerve injury in patients with leprosy. Here, we investigated mechanisms of host-pathogen interaction in the peripheral nerve lesions of leprosy. We found that the expression of the C-type lectin, CD209, known to be expressed on tissue macrophages and to mediate the uptake of M. leprae, was present on Schwann cells, colocalizing with the Schwann cell marker, CNPase (2′,3′-cyclic nucleotide 3′-phosphodiesterase), along with the M. leprae antigen PGL-1 in the peripheral nerve biopsy specimens. In vitro, human CD209-positive Schwann cells, both from primary cultures and a long-term line, have a higher binding of M. leprae compared to CD209-negative Schwann cells. Interleukin-4, known to be expressed in skin lesions from multibacillary patients, increased CD209 expression on human Schwann cells and subsequent Schwann cell binding to M. leprae, whereas Th1 cytokines did not induce CD209 expression on these cells. Therefore, the regulated expression of CD209 represents a common mechanism by which Schwann cells and macrophages bind and take up M. leprae, contributing to the pathogenesis of leprosy.The interaction between a microbial pathogen and distinct host cells is a crucial step in the initiation of the immune response and also contributes to the pathogenesis of the disease. In the human disease leprosy, the pathogen Mycobacterium leprae infects at least two cell types, macrophages and Schwann cells, both contributing to disease pathogenesis. The mechanism of Schwann cell infection includes interaction of M. leprae-specific phenolic glycolipid 1 (PGL-1) with laminin 2 in Schwann cell basal lamina and also with the ERBB2 receptor on the cell surface of Schwann cells (36). Infection of Schwann cells by M. leprae contributes to inflammation in leprosy, involving antigen presentation and Toll-like receptor (TLR)-mediated cytokine release (24, 32). The uptake of M. leprae by Schwann cells results in demyelination and subsequent nerve damage in leprosy, a major cause of patient morbidity (35).In contrast to the receptors that mediate uptake of M. leprae by Schwann cells, macrophages use a distinct set of cell surface receptors to facilitate phagocytosis. Among these is the C-type lectin receptor, CD209, also known as DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin), which mediates recognition of several pathogens, including viruses, fungi, and bacteria (8). CD209 facilitates cell binding to several species of mycobacteria, including M. tuberculosis, M. bovis, and M. leprae (9, 20, 30). The recognition of mycobacteria by CD209 has been shown to be mediated by interaction with the mycobacterial mannose-capped lipoarabinomannan (Man-LAM) (9). Although originally identified on in vitro-derived dendritic cells (DCs), CD209 is expressed by macrophages in leprosy lesions and was shown to be required for optimal binding and uptake of mycobacteria by macrophages (16).To investigate the mechanisms of pathogen recognition and subsequent inflammation in peripheral nerves in leprosy, nerve fibers can be studied in skin biopsies of leprosy patients; however, the immunopathology of these lesions involves both cutaneous and neural granulomas. As such, so-called “neural leprosy” provides an excellent model, because it is a form of leprosy that involves only peripheral nerves. In the present study, we investigated the C-type lectin, CD209, at the site of disease in neural leprosy to explore the mechanisms that contribute to the infection of Schwann cells and inflammation of peripheral nerves in leprosy.