Investigation of serological cross-reactivity within the alphavirus genus using IFA biochip mosaics

Abstract

Purpose: The alphavirus genus comprises several human pathogens, e.g. chikungunya virus (CHIKV), Ross River virus (RRV) and Eastern equine encephalitis virus (EEEV). Depending on the antigenic relatedness cross-reactivity in serological assays is commonly observed. Due to overlapping geographical distribution and similar clinical pictures a serological differentiation is desirable. Methods & Materials: Human serum or plasma samples from different geographical areas and precharacterised for IgG and IgM antibodies against various alphaviruses were investigated with multiplex indirect immunofluorescence assays. The method is based on a mosaic of up to nine biochips which carry infected or transfected cell lines each expressing antigens of another alphavirus. The samples were tested for the presence of specific IgG and IgM antibodies and endpoint titers were determined for every virus in parallel. Results: Investigation of samples from patients with different alphavirus infections led to a significant amount of cross-reactivities on IFA biochip mosaics, especially regarding IgG antibodies. Using parallel endpoint titration it was possible to determine the causative alphavirus in the vast majority of samples. For example, investigating samples from RRV infected patients, 93% and 11% reacted positive on CHIKV infected cells regarding IgG and IgM antibodies, respectively. Regarding samples from Barmah-Forest virus (BFV) infected patients, 28% and 3% were positive on CHIKV for IgG and IgM, respectively. By comparison of the endpoint titers for the respective viruses resulting from the same incubation on a biochip mosaic, 88% of RRV IgG samples and all IgM samples showed an at least ten times higher titer on the RRV biochip than on the CHIKV biochip. Regarding BFV patients, all samples showed at least ten times higher titers for BFV than for CHIKV in both IgG and IgM investigation. Conclusion: Cross-reactivity of IgG and IgM antibodies plays an important role in serological diagnostics of alphavirus infections. Parallel investigation of a sample using different alphavirus antigens in a biochip mosaic can identify the causative virus in most of the cases, depending on the antigenic relatedness of the viruses.