Immunohistochemical investigation of the cellular infiltrates at the sitesof allergoid-induced late-phase cutaneous reactions associated with pollenallergen-specific immunotherapy

Background Reduction in the size of the allergen-induced late-phase reactio n (LPR) is seen as a consequence of successful allergen specific immunother apy. Objective It was the aim of this study to characterize the cellular infiltr ate at the sites of cutaneous LPR that may occur following injection of a d epot pollen allergoid (Allergovit(R)) during immunotherapy and thereby dete rmine the immunological nature of the response. Methods Punch biopsies were taken 24 h after subcutaneous injection of a de pot pollen allergoid from eight patients that showed LPR and a further five patients that did not. Additional biopsies taken 24 h after injection of a llergoid-free depot in the same patients served as controls. Immunoenzymati c labelling of the cryostat sections with different antibodies was performe d with the APAAP technique. Results were expressed as cells/field (400 x ma gnification). Results Similar dermal cellular infiltrations were seen following depot all ergoid injections in patients both with and without LPR. Patients with LPR showed statistically significant increases in total cells, CD4(+) cells, CD 11c(+) cells, CD45RO(+) cells, CD45RB(+) cells and activated eosinophils at the reactions sites as compared with control sites. In patients without LP R CD11c(+) cells, HLA-DR+ cells and CD45RA(+) T cells increased significant ly. CD8(+), CD1a(+), NP57(+), CD23(+) and CD25(+) cells did not differ sign ificantly in either group. Conclusion These results indicate that activation of T cells, monocytes/mac rophages and eosinophils at the sites of LPR following injection of depot a llergoid are comparable with those following injection of allergen. Even in the absence of a cutaneous LPR, subsets of T cells and monocytes/macrophag es increased. These cell activations may reflect events associated with the mechanisms of allergoid-based specific immunotherapy, and suggest that at least part of the late-phase reaction may be independent of IgE.