Molecular Characterization and Gene Expression Profiling ... - CUSAT

Chapter 5
must firstly rest on a sound functional basis to target those aspects of the
innate system that pathogens might evade. It then must induce or enhance
this response to effect pathogen destruction or elimination without detriment
to the host itself (Smith et al., 2003).
Many of the compounds claimed to have immunostimulating or
potentiating effects are known from invivo or invitro experiments to have
direct effects on various aspects of the crustacean immune system. Glucan,
LPS, bacteria and other non-self agents are known to invoke various invivo
responses, such as change in haemocyte counts (Smith et al., 1984; Holmblad
and Soderhall, 1999; Lorenzon et al., 1999) and induction of encapsulation
reactions (Smith and Ratcliffe, 1980). They also are known to induce
prophenoloxidase activation and melanisation reactions (Smith and
Soderhall, 1983; Soderhall et al., 1986) while invitro glucans have been shown
to initiate cell degranulation and to enhance phagocytosis (Smith and
Soderhall, 1983; Soderhall et al., 1986). Research on a number of crustaceans
has further demonstrated that phenoloxidase activation by glucans or other
non-self molecules generates a range of immunoactive agents and activities,
including peroxinectin and reactive oxygen species (Holmblad and
Soderhall, 1999). However, the molecular mechanisms by which
immunostimulants affect the expression of immune genes still remains less
understood.
Yeasts and β-glucans are widely accepted as immunostimulants in the
shrimp industry. Yeast is generally considered as a good source of protein,
nucleic acid, vitamins and polysaccharides. Yeast supplement as
immunostimulant is believed to protect the cultured organism against the
negative effects of stress on the immune system (Burgents et al., 2004).
Previous works by Scholz et al., 1999, showed that other diets, with different
yeast additives, which were recorded as enhancing survival, were not found
to be significantly better than the control diet. Curiously, these authors
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