of the cellular immunity
in cephalopods [20] and our findings support their role in the immunological
responses to infection.Moreover, the present findings suggest
that in the common octopus circulating haemocytes are sensitive to
bacterial LPS as it occurs in other aquatic invertebrate species [12].
These preliminary results set the basis for further analyses on haemocyte
activity (e.g. chemotaxis and phagocytosis assays) as a direct measure of
the increased cell-mediated immunity here suggested. It is noteworthy
that a significant increase, though lower than in treated individuals, of
circulating haemocytes was detected also in sham-injected animals, indicating
a general effect of manipulation (anaesthesia and/or successive
haemolymph samplings). A similar effect has been found in the lesser octopus
[18]. However, in this species the increase of haemocytes in control
animals over successive samplings is more than two fold higher than that
recorded in our experiment, suggesting that the common octopus has
higher tolerance to manipulation than E. cirrhosa.
With respect to the measure of serum lysozyme activity results
highlighted a higher variability and a less clear response than circulating
haemocytes. Indeed, despite a significant increase of serum lysozyme
activity in treated animals 4 h after treatment, the two groups of
sham-injected and treated animals showed similar level of activity
after injection and these levels remained significantly high also 24
after the injection. Studies on immune stimulation in othermollusc species
reported ambiguous results about serumlysozymeactivity patterns
[38]. In the lesser octopus the treatment with the living bacterium
V. anguillarum affects haemolymph lysozyme activity only in the branchial
heart tissues 48 h after treatment [18]. Further measurements,
such as antimicrobial peptide synthesis and anti protease-activity, could
be important in clarifying the pattern of humoral response in octopus.