The effect of specific immunotherapy on the expression of costimulatory molecules in late phase reaction of the skin in allergic patients.

Background: Specific immunotherapy (SIT) modulates immune responses to allergens resulting in improvement of allergic symptoms. However, the mechanisms behind the clinical changes are not clear. Participation of costimulatory molecules on antigen-presenting cells and T cells in the process of antigen recognition is suggested to be of essential importance. The SIT effect on expression of costimulatory molecules has not been earlier examined.

Methods: Forty-one birch-allergic patients were treated with SIT or placebo. After 1 year of treatment skin biopsies were obtained 24 h following allergen challenge. Sections were stained with antibodies against: EG2 (eosinophils), CD4 (T cells), CD68 (macrophages), CD1a (Langerhans cells), CD28 (on T cells) and costimulatory molecules (CD80, CD86).

Results: Following allergen challenge number of the CD4(+) and CD68(+) cells increased significantly (P=0.002, 0.0001, respectively) in the placebo, but not in the SIT-treated patients. The difference between groups was significant (P=0.003, 0.01, respectively). The numbers of EG2(+) cells increased significantly in both groups. CD80(+) cell numbers increased in the placebo (P=0.01) but not in the SIT group. The number of CD86(+) cells increased in both groups (placebo, P=0.001; SIT, P=0.01) but significantly less in the SIT group (P=0.05). The numbers of CD28(+) cells increased in the placebo (P=0.001) but remained unchanged in the SIT group. The difference between the groups was significant (P=0.05).

Conclusion: There were lower numbers of cells expressing costimulatory molecules in SIT-treated than in placebo-treated patients. Decreased costimulation may lead to diminished immune response following allergen exposure. This could be an important factor contributing to the clinical improvement after SIT.