Abstract
The HA-1 lectin isolated from Botrylloides leachii has an amino acid composition similar to that of mammalian serum amyloid protein (SAP). SAP is a universal component of mammalian amyloid deposits. Like SAP, HA-1 has a disc ultrastructure, and antibody to HA-1 binds both (a) to amyloidlike fibers deposited between rejected Botrylloides colonies and (b) to cerebral amyloid deposits in Alzheimer's disease brains. Deposition of protochordate amyloid within rejection sites and surrounding fouling organisms implies that these fibers function as barriers to allogeneic and infectious challenge. Similarly, mammalian amyloid may also function to contain inflammatory lesions and to limit the spread of certain infections. Pathological amyloidotic conditions in humans, such as Alzheimer's disease, may result from unregulated expression of this primitive encapsulation response.
Highlights
For some years, animals belonging to the protochordate genera Botryllus and Botrylloides have been the subjects of intensive study by immunologists concerned with the evolutionary origins of the vertebrate immune response (Weissman et al, 1990)
In an examination of the ultrastructure of necrotic areas in the contacted tissues between rejecting colonies of Botryllus primigenus, Tanaka and Watanabe (1973a, 1973b) described accumulations of stiff, hollow fibers with a characteristic diameter of around 200 angstroms. These ultrastructural features are reminiscent of polymerized serum amyloid P component (SAP), which is a universal component of mammalian amyloid deposits, and of a type of fiber observed in electron micrographs of some such deposits (Skinner et al, 1982; Inoue et al, 1986)
Double-tracked fibers are concentrated in the contacted tunic tissues of rejecting oozooids, where they appear to surround degenerated test cells (Tanaka and Watanabe, 1973a, 1973b); Figs. 5 to 7
Summary
Animals belonging to the protochordate genera Botryllus and Botrylloides have been the subjects of intensive study by immunologists concerned with the evolutionary origins of the vertebrate immune response (Weissman et al, 1990) These colonial ascidians grow on hard substrata in communities where space is a limited resource and where colonies frequently come into contact. Like the closely related C-reactive protein (CRP), SAP is a member of the highly conserved pentraxin family of serum and tissue proteins (Coe, 1983) Molecules belonging to this family have been identified in several representative vertebrate classes and in an invertebrate of the protostome lineage, the horseshoe crab Limulus (Robey and Liu, 1981). No pentraxin molecule has been identified from a deuterostome invertebrate
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