OPSONIC ACTIVITY AND IMMUNOHISTOCHEMICAL LOCALIZATION OF SeC3, A COMPLEMENT COMPONENT C3-LIKE PROTEIN FROM SWIFTIA EXSERTA
Lorenzo Menzel, Florida International University
Menzel, LP, and Bigger, CH.
Department of Biological Sciences Florida International University
The third Complement component (C3) is the central protein of the complement cascade linking the three activation pathways (the antibody-dependent classical pathway, the lectin-dependent pathway, and the alternative pathway) with the lytic cascade. C3 is an evolutionarily ancient molecule involved with host defense: C3 genes have been found in many metazoan phyla. In fact our lab published the first report ofC3 from a cnidarian, the octocoral Swiftia exserta. Functional studies of complement cascade activity began with Bordet and the burgeoning field of immunology, investigating mammalian complement systems. These studies include the end-of-cascade lytic pores developed by the membrane attack complex (MAC), opsonic functions of C3b (a fragment of C3 covalently bound to targets via a thiol-ester bond), and chemo-attraction assays of C3a (as well as C4a and C5a fragments from C4 and C5, respectively). Opsonization is the labeling of particles for phagocytosis, causing opsonized particles to be ingested faster than non-opsonized particles. Several groups have expanded functional studies of the lectin-dependent complement cascade to protochordates (T Fujita and M Nonaka) and echinoderms (LC Smith), but, to date, no functional assays have been published from more basal metazoan animals. Here we demonstrate: the production of the SeC3 protein and identify some of the C3b chains by western blot analysis; the localization of C3 in the basal metazoan Swiftia exserta, by cryo-immunohistochemistry; and that opsonized zymosan particles are phogytosed more rapidly by phagocytic cells from Swiftia exserta and by RAW 237.1 cells (a mouse macrophage cell line).