Figure 1.

Immunomodulation by the viral MHC class I homolog UL18. Human cytomegalovirus encodes the MHC class I homolog UL18, which is expressed on the surface of infected cells. Interaction of UL18 with ILT2 on the surface of macrophages might result in a downregulation of cytokine production. New data suggest a further role for UL18 when it binds to ILT2 on the surface of 'killer' T cells, as this interaction inhibits the antigen-specific cytotoxicity of the T cells.