Comparative study of histamine release from skin mast cells dispersed from atopic, ascaris-sensitive and healthy dogs.

Atopic dermatitis results from the interaction between allergen and allergen-specific IgE bound to the mast cell surface receptors. This process triggers mast cell degranulation and accounts at least for early phase reaction. Furthermore, there is increasing in vitro and in vivo evidence that IgE has the ability to induce overexpression of the Fc epsilonRI receptor on the mast cell plasma membrane. In order to study the potential effect of an increase in serum IgE on mast cell activity, the histamine releasability of mature mast cells isolated from the skin of atopic, ascaris-sensitive and healthy dogs was analyzed. No histamine release was detected upon the immunological stimulation of cells that were not previously sensitized with atopic or ascaris-sensitive dog serum. However, when passively sensitized, skin mast cells were challenged with either Asc SI antigen or anti-IgE, the mast cell histamine release increased in a stimulus concentration-dependent manner. The amount of histamine released was significantly higher in response to anti-IgE than in response to Asc SI antigen. However. the difference in the percentage of mast cell histamine release between atopic (26.3+/-2.8%) and non-atopic (30.9+/-1.7%) dogs was not statistically significant, similar to what occurred when ascaris-sensitive (12.8+/-1.6%) and non-sensitive (13.2+/-1.7%) dogs were compared. Although these results could suggest that there is either little or no increase in the density of IgE receptors in atopic or ascaris-hypersensitive dogs versus controls, we strongly consider either the possibility that the digestion procedure might affect cell behaviour in vitro or that an underlying increase of receptors poorly affects the release of granule-stored mediators but influences mast cell activity in a different manner.