Meeting Abstract

17.1  Monday, Jan. 4  Chitin as a Component of the Invertebrate Immune System HEATH-HECKMAN, E.A.C.*; MCFALL-NGAI, M.J.; University of Wisconsin – Madison; University of Wisconsin – Madison heathheckman@wisc.edu

Euprymna scolopes, the Hawaiian bobtail squid, is a useful model for the study of the invertebrate immune system. Recent analyses have demonstrated that chitin breakdown products have a significant role in communication between E. scolopes and its bacterial symbiont Vibrio fischeri. To determine the source of chitin in the initiation of the association, we used a commercially available chitin-binding protein conjugated to fluorescein (CBP) to label the chitin. The only cells in contact with the symbionts that labeled with the probe were the macrophage-like hemocytes, an unexpected result; the occurrence of chitin has not previously been reported in the immune cells of any mollusc. To confirm the identity of the substrate being stained, we treated the hemocytes with a commercially available chitinase, which markedly altered the staining patterns of the chitin-binding protein, providing additional evidence that the hemocytes contain chitin. CBP labeling localized to granules in the hemocytes that also label with a halide peroxidase antibody and lysotracker, a lysosomal vital dye. In addition, hemocytes produced mRNA coding for a chitin synthase, suggesting that these cells synthesize chitin. Finally, a wide variety of invertebrate hemocytes exhibited CBP labeling patterns similar to that of E. scolopes, though vertebrates that we sampled did not. These results show that chitin can be found in invertebrate hemocytes in close proximity to canonical immune proteins and structures, providing evidence that this polysaccharide may play a conserved role in host-microbe interactions. Supported by NIH RR12294, NIH AI50661, NSF 0817232, and a NIH training grant to E.H-H.