Repositório Institucional - Unifesp :: Navegando por Palavras-chave "phagocytosis"

Navegando por Palavras-chave "phagocytosis"

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beta(2)-glycoprotein I (Apolipoprotein H) modulates uptake and endocytosis associated chemiluminescence in rat Kupffer cells
(Taylor & Francis Ltd, 2002-07-01) Gomes, L. F.; Goncalves, L. M.; Fonseca, FLA; Celli, C. M.; Videla, L. A.; Chaimovich, H.; Junqueira, VBC; Universidade de São Paulo (USP); Univ Chile; Universidade Federal de São Paulo (UNIFESP); Baylor Coll Med
beta(2)-Glycoprotein I (beta(2)GPI) is known to influence macrophage uptake of particles with phosphatidylserine containing surfaces, as apoptotic thymocytes and unilamellar vesicles in vitro. Nevertheless, effects upon macrophage activation induced by this interaction are still unknown. beta(2)GPI influence upon the reactive species production by Kupffer cells was evaluted in order to investigate whether beta(2)GPI modulates the macrophage response to negatively charged surfaces. Chemiluminescence of isolated nonparenchymal rat liver cells was measured after phagocytosis of opsonized zymosan or phorbolmyristate acetate (PMA) stimulation, in the presence and absence of large unilamellar vesicles (LUVs) containing 25 mol% phosphatidylserine (PS) or 50 mol% cardiolipin (CL) and complementary molar ratio of phosphatidylcholine (PC). beta(2)GPI decreased by 50% the chemiluminescence response induced by opsonized zymosan, with a 66% reduction of the initial light emission rate. PMA stimulated Kupffer cell chemiluminescence was insensitive to human or rat beta(2)GPI. Albumin (500 mug/ml) showed no effect upon chemiluminescence. beta(2)GPI increased PS/PC LUV uptake and degradation by Kupffer cells in a concentration-dependent manner, without leakage of the internal contents of the LUVs, as shown by fluorescence intensity enhancement. LUVs opsonized with antiphospholipid antibodies (aPL) from syphilitic patients increased light emission by Kupffer cells. Addition of beta(2)GPI to the assay reduced chemiluminescence due to opsonization with purified IgG antibodies from systemic lupus erythematosus (SLE or syphilis (Sy) patient sera. A marked net increase in chemiluminescence is observed in the presence of Sy aPL antibodies, whereas a decrease was found when SLE aPL were added to the assay, in the presence or absence of beta(2)GPI. At a concentration of 125 mug/ml, beta(2)GPI significantly reduced Kupffer cell Candida albicans phagocytosis index and killing score by 50 and 10%, respectively the present data strongly suggest that particle uptake in the presence of beta(2)GPI is coupled to an inhibition of reactive species production by liver macrophages during the respiratory burst, supporting the role of beta(2)GPI as a mediator of senescent cell removal.
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The C-terminus of murine S100A9 inhibits spreading and phagocytic activity of adherent peritoneal cells
(Birkhauser Verlag Ag, 2005-05-01) Pagano, R. L.; Sampaio, S. C.; Juliano, L.; Juliano, M. A.; Giorgi, R.; Butantan Inst; Universidade Federal de São Paulo (UNIFESP)
Objective and design: in the present study, the effect of a synthetic peptide (H-92-G(102)) identical to the C-terminus of murine S100A9 (mS100A9p) was investigated on adherent peritoneal cell function.Materials and methods: for in vitro assays, peritoneal cells were obtained from the abdominal cavity of mice and incubated, with the different concentrations of mS100A9p, for 1 h, and then their spreading and phagocytosis activities were evaluated. for ex-vivo assays, cells obtained from animals treated for 1 h with the peptide were submitted to the mannose-receptor phagocytosis assay. Shorter homologue peptides to the C-terminus of mS100A9p were also evaluated on in vitro phagocytosis assays of Candida albicans particles.Results: mS100A9p reduced both the spreading index and phagocytic activity, in vitro and ex-vivo, independent of the receptor evaluated. the homologue peptide corresponding to the H-92-E-97 region of mS100A9p, the zinc-binding motif, was responsible for such an effect.Conclusion: These results suggest a modulator effect of the C-terminus of S100A9 protein on the function of adherent peritoneal cells.
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Co-ordinated expression of lymphoid and myeloid specific transcription factors during B-1b cell differentiation into mononuclear phagocytes in vitro
(Wiley-Blackwell, 2009-01-01) Popi, Ana F. [UNIFESP]; Motta, Fabiana L. T. [UNIFESP]; Mortara, Renato A. [UNIFESP]; Schenkman, Sergio [UNIFESP]; Lopes, Jose D. [UNIFESP]; Mariano, Mario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
We previously demonstrated that B-1b cells can undergo differentiation to acquire a mononuclear phagocyte phenotype upon attachment to substrate in vitro. Here we followed the expression of surface markers and transcription factors during this differentiation. B-1b cells spontaneously express both myeloid and lymphoid restricted transcription factors. When induced to differentiate into a phagocyte, the lymphoid genes E box protein (E2A), early B-cell factor (EBF), paired box 5 (Pax5) are down-modulated, while expression of genes related to myeloid commitment is sustained. Furthermore, B-1b cell-derived phagocytes (B-1CDPs) decrease immunoglobulin M (IgM) expression but retain the expression of the heavy chain variable gene VH11 or VH12, an immunoglobulin gene rearrangement predominantly expressed by B-1 cells. the maintenance of lymphoid characteristics in B-1CDPs characterizes a unique type of phagocyte, not related to monocyte-derived macrophages.
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Differential expression of sialylglycoconjugates and sialidase activity in distinct morphological stages of Fonsecaea pedrosoi
(Springer, 2004-04-01) Alviano, D. S.; Rodrigues, M. L.; Almeida, C. A.; Santos, ALS; Couceiro, JNSS; Soares, RMA; Travassos, L. R.; Alviano, C. S.; Universidade Federal do Rio de Janeiro (UFRJ); Universidade Federal de São Paulo (UNIFESP)
The expression of sialoglycoconjugates in Fonsecaea pedrosoi conidia, mycelia, and sclerotic cells was analyzed using influenza A and C virus strains, sialidase treatment, and lectin binding. Conidium and mycelium whole cells were recognized by Limax flavus (LFA), Maackia amurensis (MAA), and Sambucus nigra (SNA) lectins, denoting the presence of surface sialoglycoconjugates containing alpha2,3- and alpha2,6-sialylgalactosyl sequences. Sialidase-treated conidia reacted more intensively with peanut agglutinin (PNA), confirming the occurrence of sialyl-galactosyl linkages. Conidial cells agglutinated in the presence of influenza A and C virus strains, which confirmed the results obtained from lectin-binding experiments and revealed the presence of sialoglycoconjugates bearing 9-O-acetyl-N-acetylneuraminic acid (Neu5,9Ac(2)) surface structures. Western blotting analysis with peroxidase-labeled LFA demonstrated the occurrence of sialylglycoproteins in protein extracts from conidia and mycelia, with molecular masses corresponding to 56 and 40 kDa. An additional band of 77 kDa was detected in conidial extracts, suggesting an association between sialic acid expression and morphogenesis. Synthesis of sialic acids was correlated with sialidase expression, since both conidial and mycelial morphological stages presented secreted and cell-associated enzyme activity. Sialoglycoconjugates were not detected in F. pedrosoi sclerotic cells from in vitro and in vivo sources, which also do not express sialidase activity. the surface sialyl residues in F. pedrosoi are apparently involved in the fungal interaction with immune effector cells, since sialidase-treated conidia were less resistant to phagocytosis by human neutrophils from healthy individuals. These findings suggest that sialic acid expression in F. pedrosoi varies according to the morphological transition and may protect infecting propagules against immune destruction by host cells.
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Effect of microcystin on leukocyte viability and function
(Elsevier B.V., 2006-06-01) Goncalves, EAP; Dalboni, Maria Aparecida [UNIFESP]; Peres, A. T.; Manfredi, A. P.; Manfredi, SR; Azevedo, S. M.; Magalhaes, V. F.; Draibe, S.; Canziani, MEF; Cendoroglo, M.; Universidade Federal de São Paulo (UNIFESP); Universidade Federal do Rio de Janeiro (UFRJ)
Microcystin (MC) has been found in several areas of the world. in addition to its hepatotoxicity, microcystin may have an immunomodulatory effect.Considering that patients receiving hemodialysis may be chronically exposed to variable concentrations of MC, and that they present important changes in this immune response, we have assessed the effect of MC on the function of leukocytes.Polymorphonuclear leukocytes isolated from health), volunteers (HV) and patients receiving hemodialysis (HD) were incubated with microcystin (10 mu g/L) for 24 h and evaluated for reactive oxygen species production (ROS), phagocytosis and apoptosis. Monocytes incubated with and without LPS (100 ng/mL) and microcystin for 24 h were assessed for TNF alpha and IL10 production.Leukocytes of HV presented an increase in apoptosis rates and leukocytes from HD exhibited a lower production of oxygen-reactive species, both spontaneously and after stimulus with S. aureus, when compared with leukocytes incubated without toxin.Monocytes presented an increase in cytokine production after stimulation by LPS in both groups, but there was no difference between the groups with and without MC that were incubated with or without LPS.Low concentrations of microcystin can induce mild changes in leukocyte function of HV and HDP, particularly in the ability to produce ROS. (c) 2006 Elsevier B.V. All rights reserved.
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Further insights into B-1 cell biology
(Medicina (buenos Aires), 2007-01-01) Mariano, Mario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Univ Paulista
The term B-1 cell was originally proposed to describe a subtype of B lymphocytes, which differs from 8 conventional cells by anatomical localization, developmental origin, surface markers expression, antibody repertoire and growth properties. B-1 cells express high levels of surface IgM, low levels of B220 (CD45R) and IgD, but not CD23, whereas conventional B-2 cells express high levels of B220 and IgD, CD23 and low levels of IgM. Besides, typical B-1 cells residing in peritoneal cavity also express low levels of Mac-1 (CD11b). Further, B-1 cells are sub classified in B-1a cells, which express CD5, and their phenotypic CD5(-) twins, B-1b cells. Our laboratory has demonstrated that B-1b cells proliferate in cultures of adherent mouse peritoneal cells and differentiate into a mononuclear phagocyte, provisionally named lymphophage. Yet, that these cells migrate from the peritoneal cavity to a non specific inflammatory lesion. From these observations the origin, differentiation and function of these cells in normal and pathological conditions have been intensively investigated in our laboratory. The morphology of B-1 cells, its participation in giant cell formation and granuloma development in vitro, and facilitation of murine melanoma growth will be presented and discussed.
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GP43 from Paracoccidioides brasiliensis inhibits macrophage functions. An evasion mechanism of the fungus
(Elsevier B.V., 2002-07-01) Popi, Ana Flavia [UNIFESP]; Lopes, Jose Daniel [UNIFESP]; Mariano, Mario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
Macrophages constitute one of the primary cellular mechanisms that impairs parasite invasion of host tissues. The phagocytic and microbicidal properties of these cells can be modulated by specific membrane receptors involved in cell-microorganism interactions. Gp43, the main antigen secreted by Paracoccidiodes brasiliensis (Pb), the causative agent of Paracoccidioidomycosis, is a high mannose glycoprotein. The role played by gp43 in the pathogenesis of the disease is not completely known. Here, we describe the influence of this molecule on the interaction between peritoneal murine macrophages and Pb. Phagocytosis of Pb, live or heat-killed, by adherent peritoneal cells from both, B10.A (susceptible) and A/Sn (resistant) mice, was evaluated. Addition of different concentrations of gp43 to the culture medium inhibited, in a dose-dependent pattern, phagocytosis of live or heat-killed Pb by peritoneal macrophages from both B10.A and A/Sn mice. Gp43 also inhibits phagocytosis of zymosan particles but did not interfere with the uptake of opsonized sheep red blood cells. It was also shown that both gp43 and heat-killed Pb have an inhibitory effect on the release of NO by zymosan stimulated macrophages. Finally, we demonstrated that gp43 inhibits the fungicidal ability of macrophages from both lineages. Based on these data, it is suggested that gp43 can be considered one of the evasion mechanisms for the installation of primary infection in susceptible hosts. (C) 2002 Elsevier Science (USA). All rights reserved.
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Injury switches melatonin production source from endocrine (pineal) to paracrine (phagocytes) - melatonin in human colostrum and colostrum phagocytes
(Blackwell Publishing, 2006-09-01) Pontes, Gerlandia N.; Cardoso, Elaine C.; Carneiro-Sampaio, Magda M. S.; Markus, Regina P.; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
A large number of data show that melatonin has immunomodulatory properties and is produced by immunocompetent cells; also, some evidence suggests a 'feedback' of the activated immune system on the pineal gland. in this paper, we studied immune-pineal interactions in colostrum obtained from healthy puerperae and mothers with mastitis taking into account that, (a) melatonin levels in milk reflects pineal activity and (b) colostrum quiescent mononuclear and polymorphonuclear phagocytes from healthy mothers in culture are adequate for evaluating the ability of immunocompetent cells to produce melatonin. Here we compared the diurnal and nocturnal melatonin levels in colostrum from healthy puerperae and mothers with mastitis; this is a unique noninvasive model for determining pineal activity in the proinflammatory phase of a defense response. in addition, we determined the 'in vitro' production of melatonin by colostrum immunocompetent cells stimulated by enteropathogenic Escherichia coli or zymosan. Suppression of nocturnal melatonin rise in mothers with mastitis was highly correlated with increased tumor necrosis factor-alpha (TNF-alpha) secretion. This result, interpreted taking into account the presence of the transcription factor nuclear factor kappa B in pineal gland, suggest that the proinflammatory cytokine can inhibit nocturnal pineal melatonin production. On the other hand, stimulated, but not quiescent, immunocompetent cells secreted in the colostrum produced melatonin in vitro. in addition, this production ceases after bacteria killing. These results suggest that during the response to an injury the production of melatonin can be transiently shifted from an endocrine (pineal) to a paracrine (immunocompetent cells) source.
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Interleukin-10 secreted by B-1 cells modulates the phagocytic activity of murine macrophages in vitro
(Blackwell Publishing Ltd, 2004-11-01) Popi, Ana Flavia; Lopes, Jose Daniel [UNIFESP]; Mariano, Mario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Univ Estadual Paulista
As demonstrated previously in our laboratory, B-1 cells migrate from the peritoneal cavity of mice and home to a distant site of inflammation to become macrophage-like cells. However, the influence that these cells might have on the kinetics and fate of the inflammatory process is not known. Considering that macrophages are pivotal in the inflammatory reaction, we decided to investigate the possible influence B-1 cells could have on macrophage activities in vitro. Our results show that peritoneal macrophages from Xid mice, a mouse strain deprived of B-1 cells, have higher phagocytic indexes for zymozan particles when compared with macrophages from wild-type mice. Moreover, macrophages from wild-type mice have a lower ability to release nitric oxide and hydrogen peroxide when compared with macrophages from Xid mice. Experiments using cocultures of B-1 cells and macrophages from Xid mice in transwell plates demonstrated that B-1 cells down-regulate macrophage activities. These observations also indicate that this phenomenon is not due to a physical interaction between these two cell populations. As B-1 cells are one of the main sources of interleukin (IL)-10, we demonstrate in this study that adherent peritoneal cells from Xid mice produce significantly less amounts of this cytokine in culture when compared with IL-10 production by cells from wild-type mice. When B-1 cells from IL-10 knock-out mice and macrophages from wild-type mice were cocultured in transwell plates, the phagocytic index of macrophages was not altered demonstrating that B-1 cells can influence the effector functions of macrophages in vitro via IL-10 secretion.
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Involvement of the major glycoprotein (gp43) of Paracoccidioides brasiliensis in attachment to macrophages
(Blackwell Science Ltd, 1998-12-01) Almeida, SR; Unterkircher, C. S.; Camargo, Z. P.; Universidade Federal de São Paulo (UNIFESP); UNESP
The yeast form of Paracoccidioides brasiliensis, the causative agent of a deep mycosis in humans, is known to be phagocytized by, and to multiply inside, macrophages. in this work we describe the involvement of gp43, a major antigenic protein of P. brasiliensis, in the initial steps of attachment of the fungus to macrophages. Anti-gp43 F(ab) polyclonal fragments were capable of inhibiting phagocytosis in a concentration-dependent manner. Sheep red blood cells sensitized with purified gp43 were more endocytized than SF:BC alone, and this process was also inhibited by anti-gp43 F(ab) fragments. Inhibition tests indicated the involvement of fucose and mannose residues in the phagocytosis of the fungus and of SRBC-gp43 by macrophages. Taken together, these results suggest that gp43 may be involved in the adherence and uptake of the fungus by murine peritoneal macrophages, and that this binding may be dependent on monosaccharide residues that are part of the gp43 glycoprotein.
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Melanin in the dimorphic fungal pathogen Paracoccidioides brasiliensis: effects on phagocytosis, intracellular resistance and drug susceptibility
(Elsevier B.V., 2006-01-01) Silva, M. B. da; Marques, A. F.; Nosanchuk, J. D.; Casadevall, A.; Travassos, L. R.; Taborda, Carlos Pelleschi [UNIFESP]; Universidade de São Paulo (USP); Albert Einstein Coll Med; Universidade Federal de São Paulo (UNIFESP)
The fungal pathogen Paracoccidioides brasiliensis produces a melanin-like pigment in the presence of L-DOPA in vitro. We investigated whether melanization affected yeast uptake by alveolar and peritoneal macrophages, the intracellular resistance of fungal cells and their susceptibility to antifungal drugs. the interactions of melanized and nonmelanized P brasiliensis with murine primary macrophages and J774.16 and MH-S macrophage-like cell lines were investigated. Melanized yeast cells were poorly phagocytosed by the cells even in the presence of complement. Melanization caused significant interference with the binding of cell wall components to lectin receptors on macrophages. Melanized cells were also more resistant than nonmelanized cells to the antifungal activity of murine macrophages. No difference in the susceptibilities of melanized and nonmelanized P brasiliensis to antifungal drugs was observed using the minimum inhibitory concentration (MIC) method. However killing assays showed that melanization significantly reduced fungal susceptibility to amphotericin B and also protected against ketoconazole, fluconazole, itraconazole and sulfarnethoxazole. the present results indicate that fungal melanin protects P. brasiliensis from phagocytosis and increases its resistance to antifungal drugs. (c) 2005 Elsevier SAS. All rights reserved.
Acesso aberto (Open Access)
Modulação de macrófagos mediada por lactilação e moléculas secretadas por células leucêmicas na degradação da asparaginase
(Universidade Federal de São Paulo, 2023-12-06) Pinheiro, Érika Freitas [UNIFESP]; Oliveira, Julio Cezar Franco de [UNIFESP]; Monteiro, Gisele; http://lattes.cnpq.br/5415434169379609; http://lattes.cnpq.br/5745233659737350; http://lattes.cnpq.br/4975771034203332
Diante de um cenário mundial onde o aparecimento de casos de câncer aumenta a cada ano, estudos são conduzidos em diversas áreas na busca de se entender o funcionamento da doença para desenvolver tratamentos. No caso da leucemia linfoide aguda (LLA), o uso do biofármaco asparaginase (ASNase) vem sendo feito desde a década de 1970, porém ainda existem muitas lacunas a serem preenchidas sobre o desenvolvimento da doença e o papel e funcionamento da ASNase frente às diferentes condições em que é exposta no corpo. As células leucêmicas apresentam níveis baixos da enzima asparagina sintetase (ASNS), sendo incapazes de produzir asparagina endógena. Dessa forma, quando a asparagina extracelular é esgotada pela ação da ASNase, que hidrolisa o aminoácido resultando em amônia e ácido aspártico, as células leucêmicas entram em apoptose, explicando o sucesso do tratamento com ASNase. Porém, a ASNase é degradada pela ação de células fagocíticas, e estudos demonstraram que logo após a entrada no corpo, o biofármaco se acumula em regiões ricas em macrófagos, como fígado, baço e medula óssea, onde é degradada e exposta ao sistema imune. Recentemente, estudos mostraram que o efeito Warburg pode estar relacionado com processos celulares como a polarização de macrófagos, devido à lactilação. Durante a glicólise aeróbia (fenômeno que caracteriza o efeito Warburg), a célula produz ácido lático, e a presença desse composto pode causar mudanças epigenéticas nos macrófagos, lactilando suas histonas e modulando a expressão gênica. Com isso, buscar entender se a lactilação torna os macrófagos mais propensos à degradação da asparaginase pode auxiliar no desenvolvimento de estratégias para prolongar a meiavida sérica da enzima. Esse projeto buscou também entender como os fatores presentes no microambiente tumoral podem afetar a polarização dos macrófagos e se isso afeta no reconhecimento da ASNase. Para isso foram incubadas células THP1 com PMA por 24 horas para induzir o perfil M0. Em seguida, os macrófagos foram expostos a quatro tratamentos por 24 horas: PBS (manutenção M0), Lactato ou IL4 (polarização M2) e LPS + IFNγ (polarização M1). Após esses tratamentos, foi adicionado 100 nM de ASNase e sua atividade residual foi medida após 1, 4 e 24 horas para observarmos se os macrófagos degradaram mais ou menos a enzima dependendo de sua modulação. O mesmo experimento foi realizado adicionando além dos tratamentos, o sobrenadante das células MOLT4, para saber se o microambiente tumoral também poderia afetar a atividade dos macrófagos frente a ASNase. Os resultados obtidos demonstraram que sem a influência do sobrenadante tumoral o perfil M2 foi o que mais degradou a ASNase. Os dados também sugerem que moléculas secretadas pelos macrófagos podem ativar a atividade da ASNase, independente do fenótipo. O experimento utilizando sobrenadante tumoral mostra que após 1 hora já é possível observar diferenças nas atividades dos macrófagos, podendo significar que alguma molécula secretada pelas células cancerígenas induz uma aceleração no metabolismo dos macrófagos fazendo com que eles aumentem a secreção de moléculas que causam uma maior atividade da ASNase. Nessa condição, a ASNase é primeiramente degradada por macrófagos M0 (1 hora) e, posteriormente, (4 horas) por M1 e M2.
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Mouse B-1 cell-derived mononuclear phagocyte, a novel cellular component of acute non-specific inflammatory exudate
(Oxford Univ Press, 2001-09-01) Almeida, Sandro Rogério de [UNIFESP]; Aroeira, L. S.; Frymuller, E. [UNIFESP]; Dias, Maria Ângela Amorim [UNIFESP]; Bogsan, Cristina Stewart Bittencourt [UNIFESP]; Lopes, José Daniel [UNIFESP]; Mariano, Mario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Inst Nucl & Energet Res
At least three B cell subsets, B-1a, B-1b and B-2, or conventional B cells are present in the mouse periphery. Here we demonstrate that B-1 cells spontaneously proliferate in stationary cultures of normal adherent mouse peritoneal cells. B-1 cells were characterized by morphology, immunohistochemistry and flow cytometry. IgM was detected in the supernatants of these cultures. We demonstrated that the major cell population analyzed expresses the B-1b phenotype. When these cells were transferred to a new culture, a large proportion of them adhere to the plastic surface, and spread as bipolar cells endowed with the capacity to phagocytose via Fe and mannose receptors. Flow cytometry analysis of these adherent cells demonstrated that the great majority of them share both B-220 and Mac-1 antigens. Nevertheless, 45% of them were exclusively Mac-1(+). Finally, when they were labeled in vitro with [H-3]thymidine and transferred to the peritoneal cavity of naive mice, they migrate to a non-specific inflammatory focus induced by a foreign-body implant. These data demonstrate that B-1 cells, mainly B-1b cells, not only proliferate and differentiate into a mononuclear phagocyte in vitro, but also that they exit the peritoneal cavity and migrate to a non-specific inflammatory milieu.
Acesso aberto (Open Access)
Phagocytosis and killing of epidemic methicillin-resistant Staphylococcus aureus by human neutrophils and monocytes
(Brazilian Society of Infectious Diseases, 2004-02-01) Salgado, M.m.; Pignatari, Antonio Carlos Campos [UNIFESP]; Bellinati-Pires, R.; Adolfo Lutz Institute Immunology Section; Universidade Federal de São Paulo (UNIFESP)
Staphylococcus aureus is a pathogen that has been associated with nosocomial infections since the preantibiotic era. Since the introduction of antibiotics in medical practice in the 1940 s, methicillin-resistant S. aureus (MRSA) strains have been emerging in various parts of the world. In view of the important role of the phagocytic system in the defense against this bacteria, we decided to study phagocytosis by neutrophils and monocytes of an epidemic MRSA strain in São Paulo, Brazil, in comparison with methicillin-sensitive strains. Complement system opsonins are fundamental for efficient ingestion of the resistant and sensitive strains by both types of phagocytes. We found no association of the opsonic requirement of the MRSA strain with the multiresistance phenotype. On the other hand, the MRSA strain was found to be more resistant to the effector mechanisms of neutrophils than both sensitive strains when opsonized with fresh serum, despite the phagocytosis results. This fact suggests that the intracellular killing of S. aureus is an additional parameter of bacterial virulence, but new approaches must be implemented to study the interactions of this MRSA strain with phagocytes in order to investigate the possible factors involved in its behavior in response to neutrophil effector mechanisms.

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