Purification of rat peritoneal mast cells: occupation of IgE-receptors by IgE prevents loss of the receptors.

The effect of the purification of rat peritoneal mast cells through three different density media (bovine serum albumin (BSA), Ficoll, and Metrizamide) was examined with respect to a) the number and affinity of immunoglobulin E (IgE)-specific receptors, and b) the ability of the purified cells to release histamine in response to the secretagogues anti-IgE, antigen, compound 48/80 and the calcium ionophore A 23187. The principal findings of this study are: 1) Purification of rat mast cells through any of the density media results in the loss of 50 to 80% of the IgE-receptor binding activity; receptors remaining active on the cells have the same affinity constant for IgE as do those on unpurified cells. 2) IgE that is bound to rat mast cells before purification remains on the purified cells. 3) Purified rat mast cells will release histamine in response to anti-IgE (without sensitization). 4) Purified cells will not release histamine in response to antigen (ovalbumin) when the cells are passively sensitized with anti-ovalbumin after purification. 5) Mast cells that are sensitized with anti-ovalbumin before purification will release histamine upon challenge with antigen after purification, although the method of purification affects the degree of release. The conclusions drawn from these findings are that IgE-specific receptors on rat mast cells are either shed or inactivated by sedimentation through BSA, Ficoll, or Metrizamide, and that the loss of these receptors is prevented by occupying them with IgE. Of the three media described for purifying rat mast cells, Metrizamide appears to be the vehicle of choice.