We propose to conduct mechanistic studies of anti-IgE therapy. The objectives are to address how anti-IgE therapy works and how it might affect the immune system in general. The proposed studies also take advantage of this well-defined therapy to address some basic questions regarding the immune system. Our hypothesis is that anti-IgE therapy may have general effects on the immune system, such as reduced IgE-mediated antigen presentation by antigen-presenting cells and suppressed allergen-specific IgE and IgG production. The specific aims of the proposed research are: