<prompt> HLA B27 is positive inAnkylosing spondylitisRheumatoid ahritisSLEBehcet syndrome  <response>: Ref Robbins 8e p193; Harrison 17e p2051 ;9e p215 The HLA complex, which is located on the sho arm of human chromosome 6, contains sequences encoding about 100 genes, most involved in the regulation of the immune response. HLA genes are classically grouped into three major classes. 