IgG4 is a subclass of IgG, which is involved in anti-inflammatory responses and its production is increased under Type 2 helper T cell (Th2) type immune responses. Systemic plasmacytosis (SP) is a rare skin disorder, which shows marked plasma cell infiltration into the dermis. Since prominent IgG4 positive cell infiltration is reported in some SP cases, the relationship between SP and IgG4-related diseases (IgG4-RD) has recently been argued. Thereby we evaluated IgG+ and IgG4+ cell number and IgG4+/IgG+ cell ratio per filed of SP and examined whether it would meet the diagnosis criteria of IgG4-RD (IgG4+/IgG+ cell ratio>40% and IgG4+ cell per field>10). Four SP cases and six other plasma cell infiltrating diseases (epidermal cyst, soft fibroma, systemic lupus erythematosus, cheilitis granulomatosa, sqamous cell carcinoma, IgG4-related disease) were studied. The number of IgG+ and IgG4+ infiltrating cells within 3 different high power field was counted in each section, and the average IgG4+/IgG+ cell ratio was calculated. In addition, we reviewed IgG4+/IgG+ cell ratio of previously reported 10 SP cases. Only 1 SP case out of 4 met the diagnosis criteria of IgG4-RD in this study. Within 10 previously reported SP cases, 5 cases met the criteria. The cheilitis granulomatosa and sqamous cell carcinoma case also showed prominent IgG4+ infiltrating cells meeting IgG4-RD diagnosis criteria. Our results suggest that SP and IgG4-RD are different disease, and the diagnosis of IgG4-RD should be carefully made.

Evaluation of IgG4 positive plasma cell infiltration in systemic plasmacytosis and other plasma cell infiltrating skin diseases