While many long-term studies of patients on sublingual immunotherapy have shown a decrease in specific IgE in some groups, not everyone’s IgE decreases. Remember that IgE is only one measure of allergic response.
Just as IgE can be used to indicate allergic sensitivity, it can also be a late indicator of tolerance to allergens.
Immunotherapy induces the regulatory T cell, the immune cell that regulates allergic inflammation. The T cells direct the cells that make immunoglobulin, B-cells, to make protective antibodies such as IgA and IgG4. With all this immune stimulation, the IgE may actually increase in the first year of sublingual immunotherapy treatment before it decreases. Sometimes a ratio of IgE to IgG4 is used to show whether immune tolerance is developing.