Due to the amount

of IgE sensitization and low antigen doses used in our model, we could not detect syk phosphorylation. Our findings indicate that the mast cell-activating machinery was intact for a non-desensitizing antigen action, since no mediator depletion occurred with desensitization, calcium flux was restored in desensitized cells when challenged with a non-desensitizing antigen and microscopic analysis confirmed that rapid desensitization is antigen specific and does not induce anergy 27. While we do not know the exact mechanism that could explain this inhibition of receptor internalization during desensitization, it is possible that the mobility of antigen/IgE/FcεRI complexes and membrane re-arrangement could prevent their internalization, as shown by others with low doses of multivalent antigen check details 25. In addition, receptors engaged with low doses of antigen could be segregated into different compartments, preventing access to phosphorylating

molecules. Inhibitory phosphatases such as SHP-1 may not be excluded from those compartments, thus preventing phosphorylation of key molecules required for signal transduction. A time course study of SHP-1 phosphorylation in RBL-2H3 cells 28 has shown a peak at 1 min of FcεRI crosslinking and a gradually decline within 10 min. Our initial results indicated a lack of phosphorylation at 100 min. (data not shown). Further studies are planned to look for phosphorylation of SHP-1 and other ifoxetine ITIM-bearing molecules 29, 30 at each step of the desensitization Decitabine in vitro protocol since it may be transient. In conclusion, this model of rapid IgE desensitization is effective

and reproducible and provides an optimal dose–time relationship, leading to almost complete abrogation of early- and late-phase activation events. This model of antigen-specific desensitization disables the specific response to one antigen but keeps the cell machinery unaffected, unlike non-specific desensitization. Most importantly, we show here that specific rapid desensitization inhibits internalization of the antigen/IgE/FcεRI complexes. The lack of severe anaphylactic reactions in our previous clinical reports 4, 5, including hundreds of desensitizations using a modified protocol, illustrates a profound inhibition of acute and delayed mast cell activation. These studies provide proof of concept for the effectiveness and specificity of human desensitizations. BMMCs derived from femurs of male BALB/c mice 8–12 wk old (Jackson Laboratory) were cultured in RPMI 1640 medium supplemented with 10% FBS, 2 mM L-glutamine, 1% Penicillin-Streptomycin, 0.1 mM MEM nonessential amino acids (all from Sigma-Aldrich) and 10 ng/mL of IL-3. IL-3 was obtained from supernatants of 293T cells expressing mouse IL-3 31, 32.