Allergen-sensitization in vivo enhances mast cell-induced inflammatory responses and supports innate immunity.

Mast cells are immune cells that play a crucial role in inflammatory reactions related to allergic reactions and the defense against certain parasites and bacteria. In allergy, the binding of immunoglobulin E (IgE) to its high-affinity receptor (FcepsilonRI) sensitizes mast cells. Subsequent cross-linking of IgE-FcepsilonRI by multivalent antigen results in cellular activation and the release of proinflammatory mediators. Recent in vivo and in vitro experiments suggest that IgE not only acts as an allergen sensor, but also induces molecular and biological changes in mast cells. In the present study we examined whether allergen-sensitization in vivo could modify the magnitude of mast cells-induced inflammatory responses. Moreover, we studied changes in peritoneal mast cell number and histamine amount during and after sensitization. We provided evidence that sensitization, at the time of the maximum allergen-specific IgE-titer, increases the intensity of a local inflammatory process generated in a cutaneous anaphylactic reaction. Sensitization also supports innate immunity, improving survival and speeding up the resolution of an acute inflammatory reaction induced by polymicrobial sepsis, while decreasing the amount of histamine in peritoneal mast cells. In addition, our results showed that sensitization induces a late increase in the number and histamine amount of peritoneal mast cells. Thus, our findings clearly demonstrated that sensitization induces changes in mast cells which prepare the cell to induce more intense inflammatory responses. This entails an increased detrimental role in subsequent IgE-dependent allergic reactions and an improved protective function in innate defense against pathogens.