Results
For the detection of antibodies against OPXV in low sample numbers, IFA
is the assay of choice and was the first assay adapted to detect
antibodies against MPXV in serum samples. To verify the antibody
cross-reactivity, cells infected with different OPXV (MPXV, CPXV and
VACV) were used to detect IgG and IgM antibodies by IFA. Moreover, in
addition to sera from MPXV-infected individuals, sera were analysed from
individuals with CPXV infection or from individuals that were recently
vaccinated against poxviruses by using the IMVANEX vaccine. Using the
different OPXV IFAs, IgG antibodies binding to MPXV, CPXV and VACV could
be detected with comparable titres in all samples (Figure 1A). Although
some differences could be observed for some sera when tested on MPXV-,
CPXV- or VACV-infected cells, no clear trend could be seen for homologue
serum/antigen sets when IgG and IgM were considered, as most sera gave
similar results irrespective of the virus strain used as antigen. The
only exception was for IgG where slightly higher titres could be seen
after MPXV infection on MPXV IFA slides. However, differences were minor
(usually a single 1:4 dilution step of the serum in the IFA). The same
pattern was observed for IgM antibodies (Figure 1B).