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Trypanosoma rangeli: a new perspective for studying the modulation of immune reactions of Rhodnius prolixus.

Garcia ES, Castro DP, Figueiredo MB, Genta FA, Azambuja P - Parasit Vectors (2009)

Bottom Line: Insects are exposed to a wide range of microorganisms (bacteria, fungi, parasites and viruses) and have interconnected powerful immune reactions.Although insects lack an acquired immune system they have well-developed innate immune defences that allow a general and rapid response to infectious agents.Over the last few decades we have observed a dramatic increase in the knowledge of insect innate immunity, which relies on both humoral and cellular responses.However, innate reactions to natural insect pathogens and insect-transmitted pathogens, such as parasites, still remain poorly understood.In this review, we briefly introduce the general immune system of insects and highlight our current knowledge of these reactions focusing on the interactions of Trypanosoma rangeli with Rhodnius prolixus, an important model for innate immunity investigation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratório de Bioquímica e Fisiologia de Insetos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Avenida Brasil 4365, Rio de Janeiro, 21045-900, RJ, Brazil. egarcia@fiocruz.br.

ABSTRACT
Insects are exposed to a wide range of microorganisms (bacteria, fungi, parasites and viruses) and have interconnected powerful immune reactions. Although insects lack an acquired immune system they have well-developed innate immune defences that allow a general and rapid response to infectious agents.Over the last few decades we have observed a dramatic increase in the knowledge of insect innate immunity, which relies on both humoral and cellular responses. However, innate reactions to natural insect pathogens and insect-transmitted pathogens, such as parasites, still remain poorly understood.In this review, we briefly introduce the general immune system of insects and highlight our current knowledge of these reactions focusing on the interactions of Trypanosoma rangeli with Rhodnius prolixus, an important model for innate immunity investigation.

No MeSH data available.


Related in: MedlinePlus

A serine proteinase cascade is activated when different receptors recognize pathogen-associated molecular patterns (PAMPs). These serine proteases hydrolyze and activate the prophenoloxidase-activating proteinase precursor (proPAP) to prophenoloxidase-activating proteinase (PAP) that can be inhibited by serpins (proteinase inhibitors). The enzyme PAP hydrolyses prophenoloxidase (PPO) releasing phenoloxidase (PO). PO oxidizes tyrosine to dihydroxyphenylalanine (DOPA) and subsequently into quinones, the precursors of melanin, cytotoxic products and encapsulation of pathogens.
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Figure 2: A serine proteinase cascade is activated when different receptors recognize pathogen-associated molecular patterns (PAMPs). These serine proteases hydrolyze and activate the prophenoloxidase-activating proteinase precursor (proPAP) to prophenoloxidase-activating proteinase (PAP) that can be inhibited by serpins (proteinase inhibitors). The enzyme PAP hydrolyses prophenoloxidase (PPO) releasing phenoloxidase (PO). PO oxidizes tyrosine to dihydroxyphenylalanine (DOPA) and subsequently into quinones, the precursors of melanin, cytotoxic products and encapsulation of pathogens.

Mentions: The prophenoloxidase (PPO) cascade, which leads to melanization and production of highly reactive and toxic compounds (e.g. quinones), is another important humoral immune reaction in insects. Also, there are several papers reporting that phenoloxidase (PO) promotes cellular defence reaction like phagocytosis [for review see [15]]. Although in some cases, the melanization process is not important for clearing an infection, it is relevant for pathogen encapsulation [15]. Melanization depends on tyrosine metabolism. The PPO activation cascade is composed of several proteins, including PPO, serine proteases and their zymogens, as well as proteinase inhibitors. The PPO cascade is set off by the recognition of PAMPs that leads to the activation of a serine protease cascade culminating in the limited proteolytic cleavage of PPO to produce active PO that catalyzes the oxidation of tyrosine to dihydroxyphenylalanine (DOPA) which is subsequently oxidized to form dopaquinone and dopamine quinone as well as 5, 6-dihydroxyindole which have highly antibacterial activities (Figure 2). These compounds are precursors of the melanin polymer which is deposited on the surface of encapsulated parasites, hemocyte nodules and wound sites [13]. Besides the PPO activation cascade is regulated by plasma serine protease inhibitors (including members of the serpin superfamily) and active phenoloxidase (PO), this process being directly inhibited by proteinaceous factors [15,16] (Figure 2). Such regulations are essential because the products of PO activity are potentially toxic to the host.


Trypanosoma rangeli: a new perspective for studying the modulation of immune reactions of Rhodnius prolixus.

Garcia ES, Castro DP, Figueiredo MB, Genta FA, Azambuja P - Parasit Vectors (2009)

A serine proteinase cascade is activated when different receptors recognize pathogen-associated molecular patterns (PAMPs). These serine proteases hydrolyze and activate the prophenoloxidase-activating proteinase precursor (proPAP) to prophenoloxidase-activating proteinase (PAP) that can be inhibited by serpins (proteinase inhibitors). The enzyme PAP hydrolyses prophenoloxidase (PPO) releasing phenoloxidase (PO). PO oxidizes tyrosine to dihydroxyphenylalanine (DOPA) and subsequently into quinones, the precursors of melanin, cytotoxic products and encapsulation of pathogens.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2719633&req=5

Figure 2: A serine proteinase cascade is activated when different receptors recognize pathogen-associated molecular patterns (PAMPs). These serine proteases hydrolyze and activate the prophenoloxidase-activating proteinase precursor (proPAP) to prophenoloxidase-activating proteinase (PAP) that can be inhibited by serpins (proteinase inhibitors). The enzyme PAP hydrolyses prophenoloxidase (PPO) releasing phenoloxidase (PO). PO oxidizes tyrosine to dihydroxyphenylalanine (DOPA) and subsequently into quinones, the precursors of melanin, cytotoxic products and encapsulation of pathogens.
Mentions: The prophenoloxidase (PPO) cascade, which leads to melanization and production of highly reactive and toxic compounds (e.g. quinones), is another important humoral immune reaction in insects. Also, there are several papers reporting that phenoloxidase (PO) promotes cellular defence reaction like phagocytosis [for review see [15]]. Although in some cases, the melanization process is not important for clearing an infection, it is relevant for pathogen encapsulation [15]. Melanization depends on tyrosine metabolism. The PPO activation cascade is composed of several proteins, including PPO, serine proteases and their zymogens, as well as proteinase inhibitors. The PPO cascade is set off by the recognition of PAMPs that leads to the activation of a serine protease cascade culminating in the limited proteolytic cleavage of PPO to produce active PO that catalyzes the oxidation of tyrosine to dihydroxyphenylalanine (DOPA) which is subsequently oxidized to form dopaquinone and dopamine quinone as well as 5, 6-dihydroxyindole which have highly antibacterial activities (Figure 2). These compounds are precursors of the melanin polymer which is deposited on the surface of encapsulated parasites, hemocyte nodules and wound sites [13]. Besides the PPO activation cascade is regulated by plasma serine protease inhibitors (including members of the serpin superfamily) and active phenoloxidase (PO), this process being directly inhibited by proteinaceous factors [15,16] (Figure 2). Such regulations are essential because the products of PO activity are potentially toxic to the host.

Bottom Line: Insects are exposed to a wide range of microorganisms (bacteria, fungi, parasites and viruses) and have interconnected powerful immune reactions.Although insects lack an acquired immune system they have well-developed innate immune defences that allow a general and rapid response to infectious agents.Over the last few decades we have observed a dramatic increase in the knowledge of insect innate immunity, which relies on both humoral and cellular responses.However, innate reactions to natural insect pathogens and insect-transmitted pathogens, such as parasites, still remain poorly understood.In this review, we briefly introduce the general immune system of insects and highlight our current knowledge of these reactions focusing on the interactions of Trypanosoma rangeli with Rhodnius prolixus, an important model for innate immunity investigation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratório de Bioquímica e Fisiologia de Insetos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Avenida Brasil 4365, Rio de Janeiro, 21045-900, RJ, Brazil. egarcia@fiocruz.br.

ABSTRACT
Insects are exposed to a wide range of microorganisms (bacteria, fungi, parasites and viruses) and have interconnected powerful immune reactions. Although insects lack an acquired immune system they have well-developed innate immune defences that allow a general and rapid response to infectious agents.Over the last few decades we have observed a dramatic increase in the knowledge of insect innate immunity, which relies on both humoral and cellular responses. However, innate reactions to natural insect pathogens and insect-transmitted pathogens, such as parasites, still remain poorly understood.In this review, we briefly introduce the general immune system of insects and highlight our current knowledge of these reactions focusing on the interactions of Trypanosoma rangeli with Rhodnius prolixus, an important model for innate immunity investigation.

No MeSH data available.


Related in: MedlinePlus