Different sites of B-lymphocyte activation in Anti-Jo-1 antibody associated myositis and in dermatomyositis

Objectives: In Dermatomyositis (DM) the humoral immune response is directed against perimysial and endomysial vascular elements and plays an important role in the pathogenesis. Although in anti-Jo-1 antibody associated myositis (anti-Jo-1 myositis) predominantly perimysial infiltration of T-cells and macrophages has been shown, the role of the humoral response has not yet been established.

Methods: Plasma cells (PC) and B-cells (BC) were counted in perivascular, perimysial and endomysial regions in muscle biopsies of patients with anti-Jo-1 myositis (n=4), DM (n=6) and in diseased controls including PM (n=7), IBM (n=6) as well as in healthy controls (n=3).

Results: In perivascular regions the highest percentage of PC was found in anti-Jo-1 myositis (80–90%), the lowest in DM (0–10%). In anti-Jo-1 myositis the high percentage of PC was also found in perimysial and endomysial regions. In DM however, high amounts of PC were only found in perimysial sites. In PM and IBM the percentages of PC were intermediate.

Conclusions: The data indicate that (i) the humoral immune response is different in anti-Jo-1 myositis and DM. In anti-Jo-1 myositis BC might already be activated outside of muscle tissue and plasma cells migrate into the perivascular regions. In DM the activation of BC apparently occurs during their migration from perivascular to perimysial and endomysial regions. (ii) The data also support the notion that the humoral response plays a higher role in PM and IBM than previously assumed.