Discussion
This case was characterized by the peculiar distribution pattern for active and inactive lesions of BP, which were clearly separated from each other. This may be regarded as an example of locus maioris resitentiae , indicating a site of the body that offers resistance to onset of a disease 2. In general, the concept of the phenomenon of antigenic competition has been referred to when the effects of a second vaccination may be reduced by an unrelated vaccination provided simultaneously or just shortly beforehand. Our case differs from such typical presentations, since the responsible antigen was the same.
Although information is limited regarding skin disorders, this phenomenon was already documented in the early 1970s in the field of contact hypersensitivity. Kimber et al. suggested that dendritic cells may play important roles in antigenic competition between two different antigens 1. Dearman et al. suggested the involvement of reduced secretion of interleukin-6 from dendritic cells in the lymph nodes might explain this phenomenon 3.
Haeberle et al. reported that regulatory T-cell (Treg) deficiency may induce pathogenic autoantibody reacting to 230-kD bullous pemphigoid antigen, leading to the development of autoimmune bullous disease4. Rosenblum et al. demonstrated that skin-resident memory Treg contribute to mitigating skin inflammation upon repeated antigen exposure 5. These reports altogether suggest that skin-resident memory Treg located in the area of the pre-existing eruption may be responsible for preventing the emergence of subsequent eruptions; therefore we attempted to identify Treg in the upper dermis of active and inactive lesions. CD4+ cells, potentially including inflammation-promoting cells and inflammation-inhibiting cells, infiltrated more in the active lesion than in the inactive lesion (Table 1). Conversely, CD25+ and FoxP3+ cells, mainly including Treg, infiltrated more in the inactive lesion than in the active lesion (Fig. 2c-2e). Compatible with the previous reports, our data suggest that Treg in the pre-existing lesion may inhibit the expansion of active lesion, resulting in the antigenic competition-like phenomenon in BP.