Acidosis activates complement system <i>in vitro</i>

Emeis, Michael; Sonntag, Josef; Willam, Carsten; Strauss, Evelyn; Walka, Matthias M.; Obladen, Michael

doi:10.1080/09629359890802

Cited by 23 publications

(17 citation statements)

References 16 publications

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“…Consistent with these results, Owen et al (53) have recently shown that exposure of human neutrophils to low pH values results in the production of platelet-activating factor, a strong inflammatory stimulus. Interestingly, it has also been shown that extracellular acidosis efficiently activates the alternative pathway of complement (54,55). Together, these results support the notion that acidosis is able to stimulate two of the major arms of innate immunity.…”

Section: Discussionsupporting

confidence: 75%

Extracellular Acidosis Triggers the Maturation of Human Dendritic Cells and the Production of IL-12

Martínez

Vermeulen

Euw

et al. 2007

The Journal of Immunology

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Although the development of an acidic tissue environment or acidosis is a hallmark of inflammatory processes, few studies analyze the effect of extracellular pH on immune cells. We have previously shown that exposure of murine dendritic cells (DCs) to pH 6.5 stimulates macropinocytosis and cross-presentation of extracellular Ags by MHC class I molecules. We report that the transient exposure of human DCs to pH 6.5 markedly increases the expression of HLA-DR, CD40, CD80, CD86, CD83, and CCR7 and improves the T cell priming ability of DCs. Incubation of DCs at pH 6.5 results in the activation of the PI3K/Akt and the MAPK pathways. Using specific inhibitors, we show that the maturation of DCs induced by acidosis was strictly dependent on the activation of p38 MAPK. DC exposure to pH 6.5 also induces a dramatic increase in their production of IL-12, stimulating the synthesis of IFN-γ, but not IL-4, by Ag-specific CD4+ T cells. Interestingly, we find that suboptimal doses of LPS abrogated the ability of pH 6.5 to induce DC maturation, suggesting a cross-talk between the activation pathways triggered by LPS and extracellular protons in DCs. We conclude that extracellular acidosis in peripheral tissues may contribute to the initiation of adaptive immune responses by DCs, favoring the development of Th1 immunity.

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Section: Discussionsupporting

confidence: 75%

Extracellular Acidosis Triggers the Maturation of Human Dendritic Cells and the Production of IL-12

Martínez

Vermeulen

Euw

et al. 2007

The Journal of Immunology

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“…Interestingly, previous studies have also shown that acidosis activates the alternative pathway of complement (23)(24)(25), supporting the hypothesis that two of the most important pathways of innate immunity are activated by protons.…”

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confidence: 51%

Extracellular Acidosis Induces Neutrophil Activation by a Mechanism Dependent on Activation of Phosphatidylinositol 3-Kinase/Akt and ERK Pathways

Martínez

Vermeulen

Trevani

et al. 2006

The Journal of Immunology

128

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Inflammation in peripheral tissues is usually associated with the development of local acidosis; however, there are few studies aimed at analyzing the influence of acidosis on immune cells. We have shown previously that extracellular acidosis triggers human neutrophil activation, inducing a transient increase in intracellular Ca2+ concentration, a shape change response, the up-regulation of CD18 expression, and a delay of apoptosis. In this study, we analyzed the signaling pathways responsible for neutrophil activation. We found that acidosis triggers the phosphorylation of Akt (the main downstream target of PI3K) and ERK MAPK, but not that of p38 and JNK MAPK. No degradation of IκB was observed, supporting the hypothesis that NF-κB is not activated under acidosis. Inhibition of PI3K by wortmannin or LY294002 markedly decreased the shape change response and the induction of Ca2+ transients triggered by acidosis, whereas the inhibition of MEK by PD98059 or U0126 significantly inhibited the shape change response without affecting the induction of Ca2+ transients. We also found that acidosis not only induces a shape change response and the induction of Ca2+ transients in human neutrophils but also stimulates the endocytosis of FITC-OVA and FITC-dextran. Stimulation of endocytosis was partially prevented by inhibitors of PI3K and MEK. Together, our results support the notion that the stimulation of human neutrophils by extracellular acidosis is dependent on the activation of PI3K/Akt and ERK pathways. Of note, using mouse peritoneal neutrophils we observed that the enhancement of endocytosis induced by acidosis was associated with an improved ability to present extracellular Ags through a MHC class I-restricted pathway.

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“…Accordingly, it is possible that a pH decrease was evoked at the site of infection in our mouse experiments, because of the reduced effect of SpeB on neutrophils. Several studies have found that low pH activates the complement system (42)(43)(44). Our results showed that PepO is involved in the pathological mechanism (Fig.…”

Section: Discussionmentioning

confidence: 49%

Streptococcus pyogenes Endopeptidase O Contributes to Evasion from Complement-mediated Bacteriolysis via Binding to Human Complement Factor C1q

Honda-Ogawa

Sumitomo

Mori

et al. 2017

Journal of Biological Chemistry

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Edited by Luke O'NeillStreptococcus pyogenes secretes various virulence factors for evasion from complement-mediated bacteriolysis. However, full understanding of the molecules possessed by this organism that interact with complement C1q, an initiator of the classical complement pathway, remains elusive. In this study, we identified an endopeptidase of S. pyogenes, PepO, as an interacting molecule, and investigated its effects on complement immunity and pathogenesis. Enzyme-linked immunosorbent assay and surface plasmon resonance analysis findings revealed that S. pyogenes recombinant PepO bound to human C1q in a concentration-dependent manner under physiological conditions. Sites of inflammation are known to have decreased pH levels, thus the effects of PepO on bacterial evasion from complement immunity was analyzed in a low pH condition. Notably, under low pH conditions, PepO exhibited a higher affinity for C1q as compared with IgG, and PepO inhibited the binding of IgG to C1q. In addition, pepO deletion rendered S. pyogenes more susceptible to the bacteriocidal activity of human serum. Also, observations of the morphological features of the pepO mutant strain (⌬pepO) showed damaged irregular surfaces as compared with the wild-type strain (WT). WT-infected tissues exhibited greater severity and lower complement activity as compared with those infected by ⌬pepO in a mouse skin infection model. Furthermore, WT infection resulted in a larger accumulation of C1q than that with ⌬pepO. Our results suggest that interaction of S. pyogenes PepO with C1q interferes with the complement pathway, which enables S. pyogenes to evade complement-mediated bacteriolysis under acidic conditions, such as seen in inflammatory sites.The human pathogen Streptococcus pyogenes is a ␤-hemolytic Gram-positive bacterium that causes a wide variety of diseases in various anatomical sites. Superficial infection of S. pyogenes generally leads to local suppurative lesions, such as seen in pharyngitis and impetigo cases. Such mucosal and skin infections are occasionally followed by onset of immune sequelae, including acute rheumatic fever and acute glomerulonephritis. Furthermore, S. pyogenes infection can also cause invasive diseases, such as necrotizing fasciitis, cellulitis, bacteremia, and streptococcal toxic shock syndrome (STSS), 2 with a high mortality rate, which has been a serious problem throughout the world (1-3).Host possesses various immune systems such as the complement system, one of the most important components of innate immunity, that contributes to host defense against pathogens, especially in the early stage of infection (4). Recognition of an invading pathogen is the trigger for complement pathway activation, and then each complement factor is activated in a sequential manner with precise control (5). Together with opsonization, complement-mediated direct killing of pathogens is attributable to formation of the membrane attack complex (MAC), which consists of late complement factors and induces bacteriolysis by pore formati...

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Acidosis activates complement system in vitro

Cited by 23 publications

References 16 publications

Extracellular Acidosis Triggers the Maturation of Human Dendritic Cells and the Production of IL-12

Extracellular Acidosis Triggers the Maturation of Human Dendritic Cells and the Production of IL-12

Extracellular Acidosis Induces Neutrophil Activation by a Mechanism Dependent on Activation of Phosphatidylinositol 3-Kinase/Akt and ERK Pathways

Streptococcus pyogenes Endopeptidase O Contributes to Evasion from Complement-mediated Bacteriolysis via Binding to Human Complement Factor C1q

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