Immune regulation during the time course of allergen-SIT. Specific immune responses are observed during the course of allergen-SIT. 1. An early desensitization effect including decrease in mast cell and basophil degranulation soon after the first administration of allergens. 2. Generation of allergen-specific Treg cells and suppression of effector cells. 3. An early increase and a late decrease in specific IgE levels. 4. A relatively early increase in specific IgG4. 5. A late decrease in type I skin test reactivity. 6. A decrease in tissue mast cell and eosinophil numbers and a release of their mediators after a few months.