A35R and H3L are Serological and B Cell Markers for Monkeypox Infection

Monkeypox virus (MPXV) resides in two forms, mature and enveloped virions, and depending on it, distinct proteins are displayed on the viral surface. We expressed in mammalian cells two MPXV antigens from the mature form and two MPXV antigens from the enveloped form and tested their reactivity to sera of 11 MPXV convalescent donors diagnosed in Israel during May-June 2022 and collected 33-62 days post infection. While only 4 out of 11 donors neutralized the related Vaccinia Lister strain, all MPXV recoverees demonstrated a strong serological response to a 124-amino acid truncation of the A35R antigen, and to a 276-amino acid truncation of the H3L antigen. Moreover, A35R- and H3L-specific B cells ranging from 0.03-0.5% and 0.01-0.35% of IgG+CD19+ cells, respectively, were detected in all 11 MPXV donors (A35R), and in 8 out of 11 donors (H3L). Therefore, A35R and H3L represent MPXV immune targets, and can be used in a simple heat-inactivated serological enzyme-linked immunosorbent assay for the identification of recent MPXV infection.