The proposed major immunological, bacteriological, and anatomical factors in RA and SpA in the setting of HIV infection
| Rheumatoid arthritis | Spondyloarthropathy | |
| MHC association—HLA-DR4 | MHC association—HLA-B27 | |
| CD4 T cells which contribute to inflammation are depleted in advanced HIV | CD8 T cells also diminish but are spared compared with CD4 cells | |
| Primary target tissue | Primary target tissue | |
| The synovial membrane | Sites of increased biomechanical stress in the joints, especially the enthesis, adjacent marrow, capsules | |
| Triggers—unknown | Triggers—bacteria/virus (including HIV) | |
| Rheumatoid factors? | Genitourinary and bowel inflammation may be commoner in homosexuals, thus allowing greater access of bacteria to the circulation | |
| Infection? | ||