Interestingly at day 24 ph, i.e. after Artemia as live feed were
introduced, transcription levels of important pro-inflammatory
cytokines (tnf-a, il-1b) were lower in the MacroGard® treated
group than in the control group. In previous studies such lowered
expression patterns of pro-inflammatory cytokines (tnf-a, il-1b)
were also observed after feeding juvenile carp for 14 and 25 days
with MacroGard® and in vitro in murine microglia cells after
treatment with b-glucan . The majority of studies regarding this
immunomodulator however describe an induction of an inflammatory
response [68,69]. The here observed anti-inflammatory
effect is also associated with reduced levels of heat shock protein
70 gene expression. This is as well in contrast to previous observations
in fish and mammals where HSP 70 protein levels were
increased after b-glucan administration . This apparent
reduction in inflammatory response (i.e. down-regulated cytokines)
and stress response (i.e. reduced hsp70 expression) in MacroGard®
fed larvae compared to the control treatment could
indicate that fish of the former group are healthier and/or possess a
health promoting intestinal microbiota. Previous histopathological
studies on turbot larvae demonstrated that intestinal lesions, which
can occur during gut development, are often associated with
mortalities due to pathogenic gut bacteria . On the other hand
Kühlwein et al. demonstrated that in carp b-glucan feeding
was associated with an altered gut microbiota and enhanced
microvilli length and density.