Invertebrates protect themselves against microbial infection by production of different antimicrobial peptides (AMPs). We previously presented the purification and characterization of two AMPs, gomesin and acanthoscurrin from the hemocytes of naïve spider A. gomesiana (J. Biol. Chem., 275: 33464, 2000; Develop. Comp. Immunol., 27: 781, 2003). Our data showed that those peptides are stored in the hemocytes granules, being 57% of them containing both AMPs.
        We are investigating where gomesin and acanthoscurrin might play a role after microbial challenge: (i) in the phagossomes, after the fusion of granules containing those AMPs or (ii) in the plasma, after their release by the hemocytes.
        We first investigated which cellular response could be activated after yeast inoculation in spider heart. Interestingly, comparing heart sections of a challenged and unchallenged spider by light microscopy, we observe a possible migration of hemocytes to the site of injury. Besides, analysis performed by transmission electron microscopy showed very few hemocytes containing internalized yeast (3 of 200 observed cells).
        Previous work showed that acanthoscurrin is secreted into the plasma after experimental infection of spiders (Develop. Comp. Immunol., 27: 781, 2003). Our data suggest that gomesin is also secreted after microbial challenge. We are performing a relative quantification of secreted acanthoscurrin and gomesin by mass spectrometry.
        The translation of gomesin into a prepropeptide raised the interest to determine where the pro-domain is cleaved. The presence of the pro-domain in the hemocytes granules, suggests that gomesin is directioned to the granules of hemocytes in a pro-peptide form. We are investigating if the processing of this peptide is intra or extracellular.
        Our results strongly suggest that during a microbial infection, hemocytes might first migrate to the site of injury and then release both AMPs, gomesin and acanthoscurrin, to kill the invading microorganisms. Phagocytosis might have a subsequently role, being responsible for the clearance of cellular debris and remodeling of damaged tissues.