Of particular importance, mice lacking FcRn or those immunized with free antigen or an antigen fused to an Fc fragment disabled in FcRn binding were not protected against HSV or HIV infection, thereby highlighting the central role of FcRn and its intact binding to IgG for efficient mucosal transport across an epithelial barrier and the elicitation of active mucosal immunization (55, 56). The gene discussed is FCGRT; the disease is HIV infectious disease.