Immunity in Achatina fulica, the giant African Land Snail.

Invertebrates have a non-clonal immune system with many similarities to the innate immune system of vertebrates. Evidence from other invertebrates, primarily insects, demonstrates that infectious challenge leads to transcriptional upregulation of a series of genes and the de novo synthesis and secretion of a battery of immune agents. These antimicrobial agents have been described as antimicrobial peptides (AMPs) even though their sizes range from 1-10kDa.

                                                                                                                        Achatina fulica, Giant African Land Snail

Epithelia are the first line of defence in invertebrate innate immunity and in Drosophila it has been demonstrated that all of the epithelial surfaces produce AMPs with a complimentary spectrum of activity (i.e. having both anti-Gram positive and anti-Gram negative activity). Given that Giant African land snails crawl over a variety of potentially contaminated surfaces and that the snail foot is the primary site of entry for pathogens, parasites and a range of opportunistic organisms, it is surprising how little we know about the defence of this epithelium. The mucus from giant African land snails contains acharan sulphate, a 29kDa glycosamino glycan, and an antimicrobial protein, achacin has now been identified. Native achacin is not bacteriolytic but appears to be bacteriostatic and has a molecular weight of 56kDa. Antimicrobial agents identified so far from a wide variety of invertebrates are typically low molecular weight (less than 10kDa) peptides suggesting that Achatina fulica is likely to have a spectrum of, as yet, unidentified antimicrobial agents.

There is much academic and commercial interest in developing novel invertebrate antimicrobial agents into products for veterinary and medical use. Currently a recombinant polyglycosylated form of achacin (rAch) with a Mr of 80kDa has shown potential for use as an antimicrobial agent.

We are using protein-based techniques to obtain a clearer view of A. fulica epithelial immunity. We are aiming to identify potential antimicrobial agents present in the mucus of Achatina fulica using antimicrobial assays, standard 2- Dimensional (2D) Polyacrylamide Gel Electrophoresis (PAGE), Difference Gel Electrophoresis (DIGE) and bacterial overlay techniques.