Figure 3: B-cell stimulation
IgE synthesis is triggered by IL-4, which is generated from activated TH2 cells. During the IL-4 stimulation the expression of CD 40 enhanced on B- lymphocytes, that binds to the CD-40 ligand. The CD-40 binding promotes the class-switch or so called isotype-switch to IgE. Besides IL-4, IL-13 even has IgE inducing function. The interaction between CD-40 and its ligand is generally classified as allergen unspecific.
The B lymphocyte is, however, not only able to synthesize immunlobulin, but also to bind IgE to its surface. Special low affinity IgE receptors (FCεRII, termed CD23 after clustering differentiation) are available for this. The binding of IgE antibodies to the low affinity receptor allows the B lymphocytes to take part in allergen-specific interactions.