The upregulation of ERAP2, an aminopeptidase that heterodimerizes and homodimerizes with ERAP1 to trim peptides prior to HLA class I loading in the endoplasmic reticulum (53) as well as shaping the cytokine response (54), highlights the upregulation of genes encoding proteins involved in antigen processing and presentation following influenza vaccination and also following YF17D vaccination (35). The gene discussed is ERAP2; the disease is influenza.