TLR2 Regulates Mast Cell IL-6 and IL-13 Production During Listeria monocytogenes Infection.

Listeria monocytogenes (L.m) is efficiently controlled by several cells of the innate immunity, including the Mast Cell (MC). MC is activated by L.m inducing its degranulation, cytokine production and microbicidal mechanisms. TLR2 is required for the optimal control of L.m infection by different cells of the immune system. However, little is known about the MC receptors involved in recognizing this bacterium and whether these interactions mediate MC activation. In this study, we analyzed whether TLR2 is involved in mediating different MC activation responses during L.m infection. We found that despite MC were infected with L.m, they were able to clear the bacterial load. In addition, MC degranulated and produced ROS, TNF-α, IL-1ß, IL-6, IL-13 and MCP-1 in response to bacterial infection. Interestingly, L.m induced the activation of signaling proteins: ERK, p38 and NF-κB. When TLR2 was blocked, L.m endocytosis, bactericidal activity, ROS production and mast cell degranulation were not affected. Interestingly, only IL-6 and IL-13 production were affected when TLR2 was inhibited in response to L.m infection. Furthermore, p38 activation depended on TLR2, but not ERK or NF-κB activation. These results indicate that TLR2 mediates only some MC activation pathways during L.m infection, mainly those related to IL-6 and IL-13 production.

Mast cells act as phagocytes against the periodontopathogen Aggregatibacter actinomycetemcomitans.

BACKGROUND: Evidence to date shows that mast cells play a critical role in immune defenses against infectious agents, but there have been no reports about involvement of these cells in eliminating periodontopathogens. In this study, the phagocytic ability of mast cells against Aggregatibacter actinomycetemcomitans compared with macrophages is evaluated. METHODS: In vitro phagocytic assays were conducted using murine mast cells and macrophages, incubated with A. actinomycetemcomitans, either opsonized or not, with different bacterial load ratios. After 1 hour, cells were stained with acridine orange and assessed by confocal laser-scanning electron microscopy. RESULTS: Phagocytic ability of murine mast cells against A. actinomycetemcomitans was confirmed. In addition, the percentage of mast cells with internalized bacteria was higher in the absence of opsonization than in the presence of opsonization. Both cell types showed significant phagocytic activity against A. actinomycetemcomitans. However, the percentage of mast cells with non-opsonized bacteria was higher than that of macrophages with opsonized bacteria in one of the ratios (1:10). CONCLUSIONS: This is the first report about the participation of murine mast cells as phagocytes against A. actinomycetemcomitans, mainly in the absence of opsonization with human serum. Our results may indicate that mast cells act as professional phagocytes in the pathogenesis of biofilm-associated periodontal disease.

Mast cell activation by conidia of Sporothrix schenckii: role in the severity of infection.

Mast cells are abundant in the skin and other peripheral tissues, where they are one of the first immune cells to make contact with invading pathogens. As a result of pathogen recognition, mast cells can be activated and release different preformed and de novo-synthesized mediators. Sporothrix schenckii is the fungus that causes sporotrichosis, a worldwide-distributed subcutaneous mycosis considered as an important emerging health problem. It remains unknown whether or not mast cells are activated by S. schenckii. Here, we investigated the in vitro response of mast cells to conidia of S. schenckii and their in vivo involvement in sporotrichosis. Mast cells became activated after interaction with conidia, releasing early response cytokines as TNF-α and IL-6. Although histamine release was not significantly stimulated by S. schenckii, we determined that conidia potentiate histamine secretion induced by compound 48/80. Furthermore, functional depletion of peritoneal mast cells before S. schenckii infection significantly reduced the severity of cutaneous lesions of the sporotrichosis. These data demonstrate that mast cells are important contributors in the host response to S. schenckii infection, suggesting a role of these cells in the progress of clinical manifestations in sporotrichosis.

Metabolic extract of Fusarium oxysporum induces histopathologic alterations and apoptosis in the skin of Wistar rats.

BACKGROUND: Most patients with Fusarium infection present with affection of the tegumentary system, with the presence of necrotic and/or inflammatory lesions associated with pain. AIM: To evaluate the effect of the intradermal application of a metabolic extract of Fusarium oxysporum in the skin of Wistar rats. METHODS: The extract was obtained from fungal cultivation in Czapek-Dox medium. It was sterilized by filtration through a Millipore membrane, and injected (0.5 mg/mL) intradermally into the skin of rats, which were killed 3, 6, 12, and 24 h after inoculation. Skin specimens were placed in paraffin and stained using hematoxylin and eosin, and toluidine blue, for the evaluation of the inflammatory response, and Sirius red for the quantification of collagen. Terminal deoxynucleotidyl transferase-mediated UTP nick end labelling (TUNEL) was used for the identification of apoptosis. Tissue reactions were graded and compared over time and compartment. RESULTS: The inflammatory reaction reached a peak at 12 h for both the dermis and subcutaneous region, being graded as moderate and moderate to severe, respectively. There was an influx of granulocytes, lymphocytes, and macrophages. A significant increase in the number of mast cells, as well as the presence of hyperemic vessels and apoptotic bodies, was observed. There was TUNEL staining in keratinocytes, fibroblasts, endothelial cells, muscles, and in the cells of the inflammatory infiltrate. There was a significant decrease in the area occupied by collagen after 12 h. CONCLUSIONS: The extract induced histopathologic alterations in the skin, probably as a result of the presence of active toxic metabolites.

Mast cell activation by Mycobacterium tuberculosis: mediator release and role of CD48.

Mast cells (MC) are abundant in the lung and other peripheral tissue, where they participate in inflammatory processes against bacterial infections. Like other effector cells of the innate immune system, MC interact directly with a wide variety of infectious agents. This interaction results in MC activation and inflammatory mediator release. We demonstrated that MC interact with Mycobacterium tuberculosis, triggering the release of several prestored reagents, such as histamine and beta-hexosaminidase, and de novo synthesized cytokines, such as TNF-alpha and IL-6. A number of M. tuberculosis Ags, ESAT-6, MTSA-10, and MPT-63, have been implicated in MC activation and mediator release. A MC plasmalemmal protein, CD48, was implicated in interactions with mycobacteria because CD48 appeared to aggregate in the MC membrane at sites of bacterial binding and because Abs to CD48 inhibited the MC histamine response to mycobacteria. Cumulatively, these findings suggest that MC, even in the absence of opsonins, can directly recognize M. tuberculosis and its Ags and have the potential to play an active role in mediating the host's innate response to M. tuberculosis infection.

Algunos aspectos del comportamiento de los mastocitos en las reacciones alérgicas dermatológicas de tipo inmediato / Some aspects of mastocyte behaviour in dermatological allergic reactions of inmediate type

De los exámenes histopatológicos realizados a nuestros ocho pacientes encontramos una notable elevación de los mastocitos, lo que es un indicio muy sugestivo de la participación de esas células en las reacciones alérgicas dermatológicas de tipo inmediato. Consideramos que los mastocitos por estar distribuido prácticamente en todos los tejidos de la economía y por las sustancias que ellos producen deben ser considerados como células de primera línea en la defensa del organismo. Teniendo en cuenta la intervención de las bitamina y serotonia en los fenómenos alérgicos es de suma importancia la investigación de estas células y los productos por ellas secretados en el campo de las alergias dermatológicas(AU)