MRC1 and head and neck squamous cell carcinoma: Because PD-L1 expression is induced in myeloid cells during HNSCC, we analysed the role of STAT1 in PD-L1 expression by CD11b+ myeloid populations including Ly6Cint Ly6G+ cells, Ly6Chi Ly6G− cells, classical M1 macrophages (Ly6C−F4/80+CD206−), and alternatively activated M2 macrophages (Ly6C−F4/80+CD206+) from the lymph nodes, spleens, and bone marrow of carcinogen induced Stat1−/− and Stat1+/+ mice.