Characterization of phage-displayed recombinant anti-idiotypic antibody fragments against coronavirus-neutralizing monoclonal antibodies.

Murine coronaviruses provide useful animal models for human neurological disorders such as multiple sclerosis. In an effort to better understand the mechanisms involved in protection from coronavirus infection, we are studying the role of the idiotypic network in the modulation of viral infectivity. We have explored the feasibility of using single-chain antibodies displayed on phage surfaces for the isolation of recombinant anti-idiotypic antibodies (anti-Ids) with antigen-mimicking properties, which has proven to be difficult with conventional hybridoma approaches. A phage-display library containing more than 10(8) different antibody specificities was screened for the presence of anti-Ids by successive rounds of panning with three different in vitro neutralizing and in vivo protective antiviral monoclonal antibodies. After five rounds of panning, between 32% and 84% of all individual clones tested showed antibody-binding in an enzyme-linked immunosorbent assay (ELISA). Although several clones showed identical antibody sequences, a number of different clones were identified and further characterized. None of the selected clones induced the production of antiviral or neutralizing antibodies or conferred reproducible protection from viral challenge in BALB/c and C57BL/6 mice. These results demonstrate that anti-Ids can be isolated from a phage-display library, although high-affinity antigen-mimicking phages with antiviral protective capacities were apparently not represented in this library. This argues for the development of more diverse phage-display libraries.