Effector Cells of Anaphylaxis: Mast Cells and Basophils

Systemic anaphylaxis arises when mast cells, possibly along with other cell types, are provoked to secrete mediators that evoke a systemic response. Mast cells in perivascular, respiratory, gastrointestinal and cutaneous tissues are likely involved, regardless of whether IgE or non-IgE-dependent pathways are invoked. Alpha/beta tryptases are selectively and abundantly produced by mast cells. Tryptase levels in the circulation provide a precise indicator of mast cell involvement. Mature beta tryptase is stored in secretory granules and is released when the cells are activated to degranulate, as occurs in anaphylaxis. Alpha/beta pro/pro' tryptases are spontaneously secreted by mast cells. Consequently, mature tryptase levels in serum (normally 1 ng/ml) are elevated in systemic anaphylaxis. Total tryptase levels (mature plus precursor forms), normally 1-15 ng/ml in baseline serum samples, are elevated in patients with systemic mastocytosis (> 20 ng/ml), a disease that also predisposes one to anaphylactic reactions. The assessment of basophils in systemic anaphylactic reactions has been problematic, because an assay for a specific releasable marker from this cell type has not been developed. Nevertheless, in cases of anaphylaxis in which elevations of histamine, but not tryptase, have been detected, it is enticing to speculate that basophil-dependent anaphylaxis may have occurred.