Antiviral defence and antibacterial proteins in the shore crab Carcinus maenas
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The defence reactions of the shore crab, Carcinus maenas, to a range of viruses were investigated in vivo and in vitro. In vivo studies with injected bacteriophages showed that C. maenas is capable of discriminating between different bacteriophages and actively removes certain phages from the haemocoele. Rapid initial clearance of the coliphage T2 was followed by slower removal and the phage persisted in the circulation for at least two weeks. The phage was sequestered to the hepatopancreas where it persisted for at least 72 h. Haemocyte counts remained unchanged upon injection of T2. With respect to prophenoloxidase activation, of the viruses tested only the Chlorella phage PBCV-1 was found to activate haemolymph prophenoloxidase at concentrations above 107 particles ml-1This indicates that C. maenas may respond to high concentrations of viruses in vitro. However, neutralization assays failed to reveal inactivation of viruses in HLS, plasma, or extracts of the hepatopancreas, gut, gill or heart, although some activity against an insect baculovirus and parainfluenza vims was detected in digestive juice. At least four antibacterial proteins, of ca. 6.5 kDa, 11.6 kDa, 20 kDa or 25 kDa, are present in C. maenas haemocytes. One, a 6.5 kDa peptide with activity against Gram positive and Gram negative bacteria, was purified. The N-terminal 30 amino acids of this peptide share over 60% sequence identity with bovine Bac 7, a mammalian cathelicidin. This 6.5 kDa peptide in C. maenas is the first antimicrobial peptide described from the Crustacea. Because the sequence of the pre-propeptide is as yet unavailable, it is not known whether or not it can be included among the cathelicidins. It has not been established whether or not the C. maenas 6.5 kDa peptide has antiviral activity.
Thesis, PhD Doctor of Philosophy
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