Analysis of the earthworm coelomocyte cell surface for the presence of Toll-like immune receptors

Coelomocytes play a central role in the earthworm immune system and are involved in immune functions characteristic of innate immunity such as phagocytosis and release of lytic factors. Earthworm coelomocytes possess several mammalian innate immune cell markers on their cell surface. Toll-like receptors (TLR) have been shown to play an important role in the activation of both the mammalian innate and adaptive immune systems and have been detected in invertebrates. In this study we used fluorescence microscopy and flow cytometry to detect the presence of fluorescent antibodies directed against TLR2, 3, 4, 6, and 9 on the cell membranes of coelomocytes isolated from Lumbricus terrestris and Eisenia fetida. We also measured TLR5 expression by exposing coelomocytes to a fluorescent bacterial flagellin, a natural TLR5 ligand. We were not able to detect binding of antibodies directed against TLR2, 3, 4, 6, or 9 on the membrane surfaces of coelomocytes. We did however detect binding of fluorescent flagellin on a small percentage of coelomocytes (10%).