Large particulate allergens can elicit mast cell-mediated anaphylaxis without exit from blood vessels as efficiently as do small soluble allergens

Aggregation makes a protein allergenic at the challenge phase of basophil-mediated allergy in mice

A hapten is a small molecule that is not immunogenic on its own but can stimulate the production of antibodies at the sensitization phase when conjugated to carrier proteins. The hapten then reacts specifically with the antibodies generated against it to elicit an immune or allergic response at the challenge phase. Here, we compared various carrier proteins conjugated with the same hapten in their ability to induce hapten-specific IgE-mediated allergic responses in vitro and in vivo, and characterized the nature of carrier proteins that determines the magnitude of response at the challenge phase of allergic reactions. Hapten 2,4,6-trinitrophenol (TNP)-conjugated ovalbumin (TNP-OVA) and bovine serum albumin (TNP-BSA) elicited TNP-specific, mast cell-dependent, immediate-type allergic reactions at a comparable level in mice that had been passively sensitized with TNP-specific IgE. In contrast, TNP-OVA but not TNP-BSA efficiently induced a basophil-dependent, IgE-mediated chronic allergic inflammation (IgE-CAI), even though both proteins could stimulate basophils in vitro at a comparable level. By comparing different carrier proteins and structurally modifying them, we found that the formation of large aggregates is crucial for TNP-conjugated carrier proteins to efficiently elicit IgE-CAI, regardless of the type of protein. Thus, the aggregation status of carrier proteins appears to determine the magnitude of allergic response at the challenge phase of hapten-specific IgE-CAI. Our findings suggest that the allergenicity of substances is a matter of importance not only at the sensitization but also at the challenge phase in a certain type of allergy including a basophil-mediated allergic inflammation.

Basophil tryptase mMCP-11 plays a crucial role in IgE-mediated, delayed-onset allergic inflammation in mice

Mice deficient for basophil tryptase mMCP-11 showed ameliorated IgE-mediated allergic inflammation with reduced leukocyte infiltration. This is the first demonstration that the basophil-derived protease plays a crucial role in allergic inflammation.

Real-time imaging of mast cell degranulation in vitro and in vivo

Mast cells undergo degranulation in response to various stimuli and rapidly release pre-formed mediators present in secretory granules, leading to immediate-type allergic reactions. Mast cell degranulation is commonly detected and quantified in vitro by measuring histamine or β-hexosaminidase released to culture medium. However, this type of assay cannot monitor degranulation of individual cells in real time, and it is not suitable for in vivo detection of degranulation. At the aim of real time imaging of mast cell degranulation at single cell level, we here developed a fluorescent protein-based indicator of degranulation, designated immuno-pHluorin (impH). When expressed in mast cells, impH is located in the membrane of secretory granules and non-fluorescent under homeostatic conditions while it turns fluorescent following degranulation, due to the pH change inside of granules during exocytosis. impH enabled us to detect polarized degranulation within one single cell when mast cells were stimulated via the small area of cell surface. Transplantation of impH-expressing mast cells into mast cell-deficient mice demonstrated that impH could function as a real-time indicator of degranulation in vivo. Thus, impH is a useful tool for imaging of mast cell activation and degranulation in vitro and in vivo, and may be applied for screening of reagents regulating mast cell degranulation.