244
M.L. Cancela et al.
Abollo et al. 2006), Enzyme Linked Immuno Sorbent Assay (ELISA; Gonzalez
et al. 1999, Schwab et al. 2001, Elandalloussi et al. 2004), or direct improvements
of PCR technique itself, like multiplexing (Shangkuan et al. 1995, Brasher et al.
1998, Penna et al. 2001) and real-time PCR (Blackstone et al. 2003, Campbell and
Wright 2003, Audemard et al. 2006). By allowing the detection of more than one
species/strain per PCR (multiplex PCR), or the precise quantification of an infection
(real-time PCR), diagnostic tools based on molecular techniques have become very
popular. Recently, a multiplex real-time PCR method has been developed to simultaneously detect and quantify infection by multiple pathogens/strains (Panicker et al.
2004, Nordstrom et al. 2007). The development of high-throughput methods will
allow in a near future rapid and simultaneous diagnostics of pathogens in a large
number of samples.
7.6.4.2 Molecular Immunity of Bivalves
Bivalves inhabit environments where they must protect themselves from an array
of commensal pathogenic and parasitic organisms. Bivalves, like other invertebrates, are deprived of an adaptative immune system (Zinkernagel et al. 1996)
and fight pathogen aggression through an innate immune response (Bachère et al.
2004). Internal defence mechanisms can be split into cell-mediated and humoral
mechanisms and it has become increasingly apparent that both are interrelated and
closely associated with hemocytes, the main immune competent cells (Cheng 1981,
Hine 1999). In order to extend our knowledge about the bivalve immune response,
genomic approaches have been developed and immune-related genes have been
characterized in several species (Gueguen et al. 2003, Tanguy et al. 2008).
Host defence response can be divided into three main steps: (i) pathogen recognition, (ii) activation of signal transduction, which induces the innate response,
and (iii) initiation of effector production mechanisms. The recognition phase is
based on the ability to discriminate between innate and exogenous agents through
receptor systems and molecules which have the ability to recognize invariant
Pathogen-Associated Molecular Patterns (PAMPs; Janeway and Medzhitov 2002).
PAMPs are exclusive to microbes and are not produced by hosts, emerging as
indispensable for microbial fitness (Nürnberger et al. 2004). Nevertheless, activation of defence mechanisms in oyster species could be triggered not only by
PAMPs but also by damage-associated molecular patterns (DAMPs), as defined
in the Matzinger damage model (Janeway and Medzhitov 2002, Matzinger 2002,
Montagnani et al. 2007). Host molecules recognizing PAMPs are called Pattern
Recognition Molecules (PRM) or Pattern Recognition Receptors (PRR; Medzhitov
and Janeway 2002, Janeway and Medzhitov 2002). In bivalves, some PRRs were
already identified, including: peptidoglycan recognition protein (PGRP; Su et al.
2007, Ni et al. 2007, Itoh and Takahashi 2008), several carbohydrate-binding lectins
(Kang et al. 2006, Wang et al. 2007a, Yamaura et al. 2008), chitin-binding lectin
(Badariotti et al. 2007), LPS-binding proteins (Gonzalez et al. 2005a, 2007, Ni et al.
2007, Bettencourt et al. 2007), receptors like Toll (Tanguy et al. 2004; Qiu et al.
M.L. Cancela et al.
Abollo et al. 2006), Enzyme Linked Immuno Sorbent Assay (ELISA; Gonzalez
et al. 1999, Schwab et al. 2001, Elandalloussi et al. 2004), or direct improvements
of PCR technique itself, like multiplexing (Shangkuan et al. 1995, Brasher et al.
1998, Penna et al. 2001) and real-time PCR (Blackstone et al. 2003, Campbell and
Wright 2003, Audemard et al. 2006). By allowing the detection of more than one
species/strain per PCR (multiplex PCR), or the precise quantification of an infection
(real-time PCR), diagnostic tools based on molecular techniques have become very
popular. Recently, a multiplex real-time PCR method has been developed to simultaneously detect and quantify infection by multiple pathogens/strains (Panicker et al.
2004, Nordstrom et al. 2007). The development of high-throughput methods will
allow in a near future rapid and simultaneous diagnostics of pathogens in a large
number of samples.
7.6.4.2 Molecular Immunity of Bivalves
Bivalves inhabit environments where they must protect themselves from an array
of commensal pathogenic and parasitic organisms. Bivalves, like other invertebrates, are deprived of an adaptative immune system (Zinkernagel et al. 1996)
and fight pathogen aggression through an innate immune response (Bachère et al.
2004). Internal defence mechanisms can be split into cell-mediated and humoral
mechanisms and it has become increasingly apparent that both are interrelated and
closely associated with hemocytes, the main immune competent cells (Cheng 1981,
Hine 1999). In order to extend our knowledge about the bivalve immune response,
genomic approaches have been developed and immune-related genes have been
characterized in several species (Gueguen et al. 2003, Tanguy et al. 2008).
Host defence response can be divided into three main steps: (i) pathogen recognition, (ii) activation of signal transduction, which induces the innate response,
and (iii) initiation of effector production mechanisms. The recognition phase is
based on the ability to discriminate between innate and exogenous agents through
receptor systems and molecules which have the ability to recognize invariant
Pathogen-Associated Molecular Patterns (PAMPs; Janeway and Medzhitov 2002).
PAMPs are exclusive to microbes and are not produced by hosts, emerging as
indispensable for microbial fitness (Nürnberger et al. 2004). Nevertheless, activation of defence mechanisms in oyster species could be triggered not only by
PAMPs but also by damage-associated molecular patterns (DAMPs), as defined
in the Matzinger damage model (Janeway and Medzhitov 2002, Matzinger 2002,
Montagnani et al. 2007). Host molecules recognizing PAMPs are called Pattern
Recognition Molecules (PRM) or Pattern Recognition Receptors (PRR; Medzhitov
and Janeway 2002, Janeway and Medzhitov 2002). In bivalves, some PRRs were
already identified, including: peptidoglycan recognition protein (PGRP; Su et al.
2007, Ni et al. 2007, Itoh and Takahashi 2008), several carbohydrate-binding lectins
(Kang et al. 2006, Wang et al. 2007a, Yamaura et al. 2008), chitin-binding lectin
(Badariotti et al. 2007), LPS-binding proteins (Gonzalez et al. 2005a, 2007, Ni et al.
2007, Bettencourt et al. 2007), receptors like Toll (Tanguy et al. 2004; Qiu et al.