Objective. Zygapophyseal joints of the spine are often affected in ankylosing spondylitis (AS). In this study, we undertook a systematic immunohistologic evaluation of the immunopathology of the zygapophyseal joints in patients with advanced AS.Methods. We obtained zygapophyseal joints from 16 AS patients undergoing polysegmental correction of kyphosis and from 10 non-AS controls (at autopsy). Immunohistologic analysis of the bone marrow was performed by analyzing the number of infiltrating T cells (CD3, CD4, CD8), B cells (CD20), osteoclasts (CD68), bone marrow macrophages (CD68), and microvessel density (CD34) per high-power field.Results. Zygapophyseal joints from 6 of 16 AS patients, but from none of the controls, exhibited 2 or more CD3؉ T cell aggregates, signifying persistent inflammation. Interstitial CD4؉ and CD8؉ T cells were significantly more frequent in AS patients compared with non-AS controls (P ‫؍‬ 0.002 and P ‫؍‬ 0.049, respectively). While there was no clear difference between the number of CD20؉ B cells in AS patients overall compared with controls, there was a significant difference when persistently inflamed joints from patients with AS were compared with joints without active inflammation from patients with AS or joints from controls (both P ‫؍‬ 0.03). Microvessel density in bone marrow from AS patients with active inflammation was significantly higher than that in bone marrow from controls.Conclusion. This immunohistologic study of bone marrow from zygapophyseal joints demonstrates persistent inflammation in the spine of patients with AS, including those with longstanding disease. The findings of increased numbers of T cells and B cells and neoangiogenesis suggest that these features play a role in the pathogenesis of AS.

Objective. Previous histopathologic and magnetic resonance imaging studies suggest that the subchondral bone marrow might be the primary site of inflammation in patients with ankylosing spondylitis (AS) and that this might be reflected by inflammation found in hip joints. The aim of this study was to conduct an immunohistologic assessment of the bone-cartilage interface and subchondral bone marrow in AS patients with hip arthritis.Methods. We collected femoral heads from patients with AS, osteoarthritis (OA), and rheumatoid arthritis (RA) who were undergoing hip replacement. The subchondral bone marrow and bone-cartilage interface were assessed immunohistochemically by evaluating infiltrating T cells, microvessel density, and osteoclasts. Areas of the femoral head surface with and without cartilage were assessed separately.Results. At sites with surface cartilage, we found subchondral infiltration of CD3؉ T cell aggregates at significantly higher numbers in AS patients as compared with OA patients, but not RA patients. At sites of complete cartilage destruction, the frequency of CD3؉ T cell aggregates was significantly reduced as compared with sites with cartilage on the surface in AS patients, but not in RA patients. Similar differences were found for CD4؉ and CD8؉ T cells. Only at sites with surface cartilage, but not those without, angiogenesis and osteoclastic foci in the subchondral bone marrow in AS patients were significantly increased as compared with RA patients and with OA patients.Conclusion. These findings suggest that the subchondral bone marrow and bone-cartilage interface are primary sites of inflammation in AS and that cartilage might be necessary for the induction of inflammation.