UL18 & B2M

Human cytomegalovirus (HCMV) encodes UL18, a viral MHC‑I homolog that mimics human HLA class I molecules. UL18 forms a stable heterodimer with human β2‑microglobulin (B2M), enabling proper folding and high‑affinity interaction with the inhibitory receptor LIR‑1/ILT2 on immune cells. This interaction suppresses NK‑cell activation and contributes to HCMV immune evasion. Recombinant UL18–B2M complexes are widely used to study viral immunomodulation and receptor–ligand interactions.