A cell‐surface opsonic receptor on leucocytes from the phylogenetically primitive vertebrate, Eptatretus stouti

Abstract

Summary A humoral recognition molecule that is homologous to the mammalian complement components C3, C4 and C5 has recently been identified in the Pacific hagfish, Eptatretus stouti. One function of this complement-like protein (CLP) is to opsonize foreign material for phagocytosis by hagfish leucocytes. Here, we demonstrate that CLP's opsonic activity can be abrogated by pre-incubating phagocytes with an anti-hagfish leucocyte mAb (IBl). Moreover, antigen-activated CLP can block the binding ofthe IBl antibody to hagfish leucocytes. Flow cytometry and immunoprecipitation indicate that IBl recognizes a 105 kDa cell-surface, monomeric protein that is expressed exclusively on phagocytic hagfish leucocytes. It is concluded that this 105 kDa protein represents the cell surface receptor by which CLP mediates the phagocytosis of opsonized targets.

Variable lymphocyte receptors in hagfish

“…Because of their unique phylogenetic position, these eel-shaped jawless fish have been studied extensively in search for the origin of vertebrate adaptive immunity. Like lamprey, the hagfish have heterogeneous blood leukocyte populations, including cells morphologically similar to mammalian lymphocytes (4)(5)(6)(7)(8)(9). Both hagfish and lamprey have been reported to produce specific agglutinins and opsonins in response to particulate antigens (9)(10)(11)(12) and to undergo accelerated rejection of second-set skin allografts (10,13).…”

“…Like lamprey, the hagfish have heterogeneous blood leukocyte populations, including cells morphologically similar to mammalian lymphocytes (4)(5)(6)(7)(8)(9). Both hagfish and lamprey have been reported to produce specific agglutinins and opsonins in response to particulate antigens (9)(10)(11)(12) and to undergo accelerated rejection of second-set skin allografts (10,13). However, neither agnathan has been shown to possess the essential components that gnathostomes use for adaptive immunity, namely Ig, T cell receptors, recombination activating genes RAG1 and -2 for V(D)J rearrangement, and MHC class I and II molecules (14)(15)(16)(17)(18).…”

MHC Class I Regulation: The Origin Perspective

“…Jawless lampreys and hagfish constitute the linage that diverged before jawed fish and are grouped in cyclostome taxon [57,58]. As the immediate ancestors of jawed vertebrate, jawless fish have been studied extensively in search for the origin of the adaptive immune system [59][60][61][62][63]. However, none of the components of jawed vertebrate adaptive immunity (immunoglobulins, T cell receptors, recombination activating genes RAG1 and 2, and MHC class I and II molecules) have been identified in this taxon.…”