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.