Binding of antigen to surface Ig on isolated rat mast cells

This study concerns observations on isolated rat mast cells sensitized to specific antigen. Specific binding of antigen to the surface immunoglobulins of these cells could be demonstrated by immunofluorescence technique as well as by radiolabelled antigen binding and the degree of binding parallelled the allergic reaction as judged by histamine release. Exposure of mast cells to antigen at both low and high antigen concentrations did not change the distribution of the surface immunoglobulins. Furthermore, neither capping not shedding could be induced, even by excessive antigen stimulation. The amount of antigen molecules bound to surface Ig was linearly correlated to the allergic histamine release. When mast cells were sensitized to two antigens of different molecular weight, the cells showed the highest sensitivity to the antigen having the highest molecular weight. These results indicate that both the amount of antigen and the molecular weight of the antigen bound to surface Ig are important factors in the allergic histamine release from mast cells, whereas surface Ig redistribution is not.