Monoclonal antibodies to specific components of the Dutch elm disease pathogen Ophiostoma ulmi

The potential of polyclonal antisera and monoclonal antibodies to differentiate the EAN and NAN aggressive subgroups of Ophiostoma ulmi was explored. Polyclonal antisera, when tested by ELISA, cross-reacted widely with unrelated species and failed to distinguish between the two aggressive subgroups but small quantitative differences were found, particularly between antigens secreted overnight, by EAN and NAN germlings. Monoclonal antibodies were raised in mice against mycelial homogenates. From two fusions, 33 cell lines were raised that secreted antibodies positive for O. ulmi. Approximately one third were non-specific; 11 were specific either to species or subspecies. Two cell lines differentiated mycelial antigens of the aggressive isolates of O. ulmi from those of the non-aggressive subgroup, but not antigens from surface washings. Only quantitative differences were detected between the EAN and NAN aggressive subgroups. Almost all the monoclonal antibodies and antiserum recognized antigens present in surface washings of cultures on solid medium, in cell-free extracts of mycelial homogenates, in cell-free culture fluids, and in substances secreted overnight by germinating spores. Specific detection of such molecules promises to provide a highly sensitive mechanism for studying early pathogen/host plant interactions. Most of the monoclonal antibodies appeared to have potential diagnostic value; they gave readings twofold to tenfold higher with extracts from diseased than from healthy tissue. However, one cell line that secreted antibodies specific to O. ulmi cross-reacted strongly with extracts of healthy tissue.