Allergen immunotherapy decreases specific allergen-induced expression of Fas and FasL on CD4+ and CD8+ cells.

Apoptosis programmed cell death without induction of an inflammatory response. It is mediated by Fas--a cell surface protein which is expressed on activated lymphocytes. Interaction with its counterpart--the Fas ligand induces the apoptosis of Fas bearing cells. The mechanism underlying successful immunotherapy has not been identified. The aim of this study was to investigate whether specific immunotherapy (SIT) might affect Fas and FasL expression after stimulation with specific allergen. The study was conducted on 8 allergic subjects and 8 healthy volunteers as controls. The allergic patients were treated with conventional SIT (Pollinex). Blood samples were collected before the first day and 7 days after the last injection. Isolated CD4+ and CD8+ cells were incubated in various concentrations of specific allergen (1, 10, 100 ng/ml) or in medium alone. Indirect immunofluorescence test with rabbit IgG against human Fas and FasL was performed. The percentage of positive cells was determined under fluorescence microscope. The expression of Fas and FasL before SIT was significantly increased on CD4+ and CD8+ cells under the influence of specific allergen (10, 100 ng/ml). After SIT, significant decrease in the expression of both molecules was observed, although elimination of allergen-reactive cells was not complete and their number was still higher than in the controls. CONCLUSION: The exposure of CD4+ and CD8+ cells on allergen may induce the Fas-FasL apoptotic pathway. Significant decrease in number of allergen-reactive CD4+, CD8+ cells after SIT suggests participation of the phenomenon in deletion of clones, which may be a part of the allergen tolerance mechanism achieved naturally or during SIT.