There is a global need to elucidate protective antigens expressed by the SARS-coronavirus (SARS-CoV). Monoclonal antibody reagents that recognise specific antigens on SARS-CoV are needed urgently. In this report, the development and immunochemical characterisation of a panel of murine monoclonal antibodies (mAbs) against the SARS-CoV is presented, based upon their specificity, binding requirements, and biological activity. Initial screening by ELISA, using highly purified virus as the coating antigen, resulted in the selection of 103 mAbs to the SARS virus. Subsequent screening steps reduced this panel to seventeen IgG mAbs. A single mAb, F26G15, is specific for the nucleoprotein as seen in Western immunoblot while five other mAbs react with the Spike protein. Two of these Spike-specific mAbs demonstrate the ability to neutralise SARS-CoV in vitro while another four Western immunoblot-negative mAbs also neutralise the virus. The utility of these mAbs for diagnostic development is demonstrated. Antibody from convalescent SARS patients, but not normal human serum, is also shown to specifically compete off binding of mAbs to whole SARS-CoV. These studies highlight the importance of using standardised assays and reagents. These mAbs will be useful for the development of diagnostic tests, studies of SARS-CoV pathogenesis and vaccine development.

Porcine monomyeloid cell lines were established following transfection of primary porcine alveolar macrophage cultures with plasmid pSV3neo, carrying genes for neomycin resistance and SV40 large T antigen. The parental clone 3D4 exhibited a relatively rapid doubling time (25.5 h), high plating efficiency and mixed phenotype with respect to growth on a solid support. Single cell cloning of the 3D4 parent resulted in establishment of several cell lines; three of them designated 3D4/2, 3D4/21 and 3D4/31 were selected for further characterization. All three clones supported the replication of vesicular stomatitis virus (VSV), pseudorabies virus (PRV), classical swine fever virus (CSFV), swine vesicular disease virus (SVDV), swine poxvirus, African swine fever virus (ASFV), herpes simplex virus (HSV), parainfluenza virus, bovine adenovirus (BAV), vaccinia virus (VV), and porcine adenovirus (PAV). Under the conditions tested the cells did not support replication of porcine reproductive and respiratory syndrome virus (PRRSV). The swine myeloid character was confirmed for all three clones by fluorescence activated cell scanning (FACS) analysis using monoclonal antibodies 74-22-15 and DH59B, which recognize the pan-myeloid antigen cluster SWC3a. A subpopulation of each cell line was positive for nonspecific esterase activity and phagocytic activity to varying degrees depending on the media formulation. Cells from all three lines exhibited anchorage dependent growth when maintained in RPMI 1640 medium supplemented with 5-15% fetal bovine serum (FBS) and nonessential amino acids. Propagation in commercially formulated serum free media resulted in colony formation and growth in suspension. The addition of dimethyl sulfoxide (DMSO) or phorbol 12-myristate 13-acetate (PMA) to serum free media restored cell attachment. DMSO was also able to induce expression of CD14 monocyte marker in the 3D4/31 cell line maintained in FBS containing medium, as determined by FACS with monoclonal antibody CAM36A. Supplementation of RPMI medium with 10% porcine serum upregulated the expression of CD14 and induced expression of porcine macrophage markers recognized by antibodies 2B10 and 2G6 (Vet. Immunol. Immunopathol. 74 (2000) 163) in all three cell lines. The porcine myelomonocytic cell lines obtained may have a wide variety of applications in porcine virology and immunology.

SUMMARYThe Quebec isolate of bovine coronavirus (BCV) was found to contain four unique major structural proteins. These proteins consisted of the peplomeric protein (gp190/E2, gpl00/E2), the nucleocapsid protein (p53/N) and its apparent trimer (pl60/N), a family of small matrix glycoproteins (gp26/E1, gp25/E1 and p23/E1) and the putative haemagglutinin (gp124/E3). Pulse-chase experiments utilizing polyclonal antiserum and monoclonal antibodies indicated that the unique BCV E3 protein had as its primary precursor an N-linked glycoprotein with an Mr of 59000 (gp59) which underwent rapid dimerization by disulphide bond formation to yield gp118. Further glycosylation of gp 118 produced gp 124/E3 which incorporated fucose. Thus gp124/E3 was probably a homodimer. The processing of the E2 and E1 proteins of BCV was similar to that shown previously for mouse hepatitis virus. A large N-linked precursor glycoprotein, gpl70, underwent further glycosylation to yield gpl90/E2 before subsequent proteolytic cleavage to yield gpl00/E2. The glycosylated E1 (gp26, gp25) proteins arose as a result of O-linked glycosylation of p23/E1 as indicated by the resistance of these species to tunicamycin.

The 38,200-molecular weight (unreduced)/41,900-molecular-weight (reduced) glycoprotein of bovine rotavirus, isolate C486, was identified as the major neutralizing antigen. This glycoprotein as well as the corresponding glycoprotein of another bovine rotavirus serotype also specifically attached to cell monolayers under normal conditions for virus adsorption in vitro. Further support for this glycoprotein being directly responsible for virus attachment to cells was that (i) infectious virus of both serotypes could compete with the C486 glycoprotein for cell surface receptors, and (ii) neutralizing monospecific antiserum and neutralizing monoclonal antibodies directed toward the glycoprotein could block this virus-cell interaction. Preliminary epitope mapping of the glycoprotein with monoclonal antibodies further localized the neutralization-adsorption domain to a peptide with an approximate molecular weight of 14,000. The effect of two protein modifications, glycosylation and disulfide bridging, on the reactivity of this peptide with antibodies and cell surface receptors was investigated. It was demonstrated that, whereas glycosylation did not appear to affect these reactivities, disulfide bridging seemed to be essential.

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