2F). Since FcεRI-mediated mitogen-activated protein kinases (MAPKs) activation leads to gene transcription of several cytokines 19, 20, we next examined the levels of phosphorylation of p38 MAPK in DNP-HSA-activated and desensitized cells (see Fig. 2F). As expected by the low levels of TNF-α and IL-6 production, p38 MAPK phosphorylation was inhibited by rapid desensitization, indicating that molecular events leading to cytokine gene transcription were inhibited during rapid desensitization. Because the duration of desensitization may depend on the presence of bound and soluble antigen, we determined the duration of, and antigen requirements for, maintaining hypo-responsiveness after

Ulixertinib purchase desensitization. Cells challenged with 1 ng DNP-HSA at 10 min, 2 h and 4 h after desensitization, remained hypo-responsive with a 20% β-hexosaminidase release (see Fig. 3A, first bar of each time group of bars). Treatment of desensitized cells with ionomycin at 10 min, 2 h or 4 h after desensitization, resulted in high levels of β-hexosaminidase release (see Fig. 3A,

second bar of each time group of bars), indicating that desensitized cells were not mediator-depleted. Further time points were not pursued due to diminishing cell viability after 6 h (from 91 to 83% viability 4 h after desensitization (100 min)). This decrease in cell viability was attributed to low volume (106 cells in 50–100 μL) and IL-3 and CO2 depletion. We then considered the Sirolimus clinical trial possibility that desensitized BMMCs could remain hypo-responsive to further stimulation due to the excess of soluble antigen. Washed and non-washed desensitized cells responded similarly to challenge (see Fig. 3B), indicating that once hypo-responsiveness was achieved the presence PRKACG of soluble antigen was not required for maintaining desensitization. Internalization of antigen/IgE/FcεRI complexes has been demonstrated after cell activation 21, 22, and it has been suggested that mast cell hypo-responsiveness to low antigen

doses is due to internalization of antigen-bound receptors 12. We wanted to determine the fate of the antigen/IgE/FcεRI complex with desensitization. We analyzed surface expression of FcεRIα and IgE in rapid-desensitized cells, in cells challenged with 1 ng DNP-HSA or with 1 ng HSA, and in non-sensitized cells. Surface expression levels of FcεRIα and IgE in desensitized cells were similar to those of cells challenged with 1 ng HSA and significantly higher than in activated cells (see Fig. 4A), indicating the impairment of internalization of IgE and FcεRIα. Since most of the IgE/FcεRI complexes remained on the cell surface, we sought to determine whether anti-IgE could crosslink free IgE on desensitized cells. DNP-desensitized cells released β-hexosaminidase when treated with anti-IgE (see Fig. 4B), indicating that unbound IgE was available for crosslinking and remained accessible.