SLC15A4 and immune system disorder: Taken together, these findings demonstrate that PHT1 (SLC15A4) plays a key role in the immune response, so it is not surprising that several studies have implicated PHT1 in the development of diseases associated with immune dysfunction, such as systemic lupus erythematosus (SLE) [18,19,20,21,22] and inflammatory bowel disease (IBD) [19].