To analyze autoantibodies against human BTN1A1, BTN2A1, BTN3A1, CD80, CD86, PD-L1 (programmed death ligand 1), and bovine BTN1A1 using novel cell-based assays in MOGAD patient sera comparing to aquaporin-4 antibody seropositive NMOSD patients and healthy controls.

Myelin oligodendrocyte glycoprotein (MOG) antibody disease is an autoimmune condition associated with antibodies against MOG. MOG belongs to the butyrophilin (BTN) family and shares significant homology with human and bovine BTNs.

Sera from 14 MOG-IgG-positive MOGAD patients were tested by cell-based assay for binding to the BTN molecules BTN1A1, BTN2A1, BTN3A1, CD80, CD86, PD-L1, and bovine BTN1A1. Sera from ten AQP4-IgG seropositive NMOSD and ten healthy individuals were used as controls.

Reactivity against BTN1A1, BTN2A1, BTN3A1, CD86, and PD-L1 was present in 78.6% (11/14), 7.1% (1/14), 64.3% (9/14), 14.3% (2/14), and 7.1% (1/14) of MOGAD patients, respectively; no serum reactivity against the BTN family was detected in the NMOSD or the healthy control groups. All 14 MOGAD cases showed similar bovine BTN1A1-IgG and MOG-IgG titers (correlation analysis R²=0.9826, P<0.0001). Serial titer measurements after immunoadsorption using MOG- or bovine BTN1A1-expressing HEK293T cells caused significant reductions in MOG-IgG, human BTN1A1-IgG, and human BTN3A1-IgG titers.

We found that MOG-IgG could bind to the other BTNs. Despite its low affinity, MOG-IgG's cross-reactivity to BTNs could modulate the genesis of autoreactivity and the characteristic pathophysiology of MOGAD.