Desensitization of IL-4 secretion from mouse bone marrow-derived mast cells

Desensitization of mast cells' secretory response to an immuno-receptor stimulus

Knowledge of the desensitization process of responses to the type I receptor for IgE (FcepsilonRI) is rather limited. We investigated whether mast cells' secretory response to this receptor's stimulus can be subjected to desensitization under protocols usually employed for hormonal or neural receptors, i.e. by excessive, prolonged or repetitive exposure to the stimulus. To study this we have employed the rat mucosal-type mast cells of the RBL-2H3 line, which enables a rigorous examination of the response to the FcepsilonRI stimulus. These cells exhibited a marked decrease of both, secretion of granule-stored and de novo synthesized mediators to an optimal stimulation, when first exposed to prolonged FcepsilonRI-IgE clustering by specific antigen (DNP(11)-BSA) or by the IgE specific mAb 95.3 at concentrations that are below the threshold of inducing secretion. The extent of desensitization depended on the employed concentrations of IgE and on the clustering agents, as well as on the length of the desensitization period. The levels of cell surface FcepsilonRI expression and of cell-bound IgE were determined following the desensitization period and no significant correlation has been observed between the extent of endocytosis and the observed desensitization. Thus, a different process, which interferes with FcepsilonRI stimulus-response coupling network, is responsible for the observed desensitization.

IgE antibody up-regulates high affinity IgE binding on murine bone marrow-derived mast cells

We have examined 3-week-old alcian blue positive cells (putatively mast cells) derived from mouse bone marrow for their expression of Fc epsilon RI. Using an indirect method of sensitizing the cells with immunoglobulin E (IgE) antibody (anti-DNP IgE) and detecting the level of bound IgE antibody by flow cytometry, we found that prolonged culture (1-5 days) with IgE, but not IgG, increased the total receptor density 6 +/- 1.9 fold. During the same period, histamine release in response to antigen (DNP-HSA) increased approximately 6-fold while the cell's response to either thrombin or ionomycin remained constant. The greatest up-regulation occurred in the first 2 days of culture. Using 2.4G2 to detect Fc epsilon RII RIII, we could not detect any up-regulation of this receptor. Culturing the cells for 1 h after sensitization did not result in any loss of cell surface IgE, suggesting a reasonably high affinity binding similar to that expected for Fc epsilon RI. This up-regulation was completely inhibited by co-culture with 2 micrograms/ml cycloheximide. These data suggest that IgE is capable of inducing a significant, protein synthesis, dependent up-regulation of its own high affinity receptor on mast cells/basophils.