IgE immune complexes stimulate arachidonic acid release by mouse peritoneal macrophages

Resident mouse peritoneal macrophages were labeled with [3H]arachidonic acid and challenged with Sephadex beads coated with immune complexes of IgE and antigen. Arachidonic acid release by the cells was assessed by the quantity or radiolabel recovered from the culture medium. Freshly isolated macrophages responded to IgE immune complexes with a release of [3H]arachidonic acid that was linear for 1-2 hr. The magnitude of the response was dependent on both the number of immune complex-coated beads and on the degree of opsonization of the beads. Under conditions of maximal stimulation, macrophages challenged with IgE immune complex-coated Sephadex released 23 +/- 4.5% of their incorporated radiolabel. This is compared to values of 34.2 +/- 0.5% and 38.1 +/- 3.3% for cultures that received IgG immune complex-coated Sephadex or zymosan, respectively. Macrophages did not release arachidonic acid upon exposure to soluble IgE and antigen given sequentially or simultaneously, and soluble IgE did not inhibit the cells' response to IgE immune complexes. Incubation of macrophages for longer than 3 hr prior to challenge resulted in a selective loss in the cells' ability to respond to IgE immune complexes. After 16 hr of culture, macrophages released only 3.9 +/- 0.3% of their incorporated 3H on exposure to IgE immune complexes; however radiolabel release in response to zymosan (42.0 +/- 0.8%) was identical to that of freshly isolated cells. These data indicate that macrophages are capable of releasing arachidonic acid in response to preformed particulate immune complexes of IgE and antigen. Because Sephadex beads are too large to be interiorized by the cells, this response results from the interaction of the immune complexes with the macrophage plasma membrane.