HLA-DRB1 and typhoid fever: however, has identified a specific locus (HLA-DRB1*405) which confers fivefold protection against developing typhoid fever.35 How genetic variation at this site influences protection against typhoid is still under investigation, but may result in functional differences in MHC class II amino acid sequences; in turn, this may influence S Typhi epitope selection and antigen presentation or the scale and format of the host’s T cell response.