Abstract
Renibacterium salmoninarum causes a chronic disease of salmonid fish known as bacterial kidney disease. High concentrations of bacterially produced extracellular protein (ECP) are present in plasma, kidney, and spleen tissue of naturally and experimentally infected fish. ECP agglutinated salmonid leukocytes in vitro at concentrations which correspond to levels found in highly infected fish. Association of biological activity with the structure of the major protein constituent of ECP, p57, was accomplished by monoclonal antibody (MAb) analysis. Location of the antigenic binding sites recognized by the MAbs was determined by two-dimensional electrophoresis and Western immunoblotting of the proteolytic breakdown fragments of p57. Eight MAbs have been classified into three groups on the basis of their differential recognition of these proteolytic breakdown products. Group I MAbs bound a region proximal to the amino terminus of the protein. Two of these MAbs were also able to block leukoagglutinating activity. Group III MAbs bound to a region associated with the bacterial cell surface, while group II MAbs bound a region between group I and group III. These analyses have allowed the identification of potential structural and functional regions of p57.