Development of chimeric monoclonal antibodies as standardised positive controls in rickettsial serodiagnosis

Rickettsial diseases present ongoing diagnostic challenges due to antigenic diversity, serological cross-reactivity, and the lack of reliable standardised control reagents. Current serodiagnostic assays frequently rely on convalescent human sera as positive controls, which are inherently variable, limited in supply, and poorly suited to assay standardisation and quality assurance. In this study, we developed and validated human-mouse chimeric monoclonal antibodies targeting the conserved outer membrane protein B (OmpB) of Rickettsia typhi as defined, renewable, positive-control calibrators for existing rickettsial serological platforms. Murine monoclonal antibodies were generated and engineered into chimeric IgG antibodies, which were expressed in HEK293T cells. The chimeric antibodies demonstrated high antigen specificity, bound native OmpB on the surface of R. typhi, and showed no detectable cross-reactivity within the tested antigen panel when evaluated using dot blot, immunofluorescence microscopy, and Luminex-based multiplex assays. Compared with patient-derived positive control sera, the chimeric antibodies demonstrated improved specificity and consistent performance within the evaluated assay conditions. These findings support the potential use of chimeric monoclonal antibodies as standardised positive controls for rickettsial serodiagnostics, with potential applications in assay validation, quality assurance, and inter-laboratory harmonisation.