Rabbit F(ab′)₂ antihuman IgE is a universal skin test reagent in the evaluation of skin mast cell degranulation in vivo

Antihuman IgE is often used to study basophil- and mast cell-mediator release in vitro but is infrequently used in vivo. To evaluate in vivo skin reactivity to anti-IgE, an affinity purified rabbit F(ab′)₂ fragment of antihuman IgE was injected intradermally in 22 nonallergic and 27 allergic,subjects. All 49 subjects (including a subject with <1 nglml of total serum IgE) had positive immediate cutaneous reactions to anti-IgE. Although total serum IgE level was weakly correlated (r = -0.51; p < 0.005) with in vivo skin reactivity to anti-IgE for the entire population, allergic subjects did not have significantly increased skin reactivity compared to nonallergic subjects (p = 0.18), despite having higher total serum IgE levels (p < 0.002). A late-phase cutaneous response (LPR) to anti-IgE occurred in 60% of the allergic and in 50% of the nonallergic subjects. Subjects with an LPR required approximately tenfold higher concentrations of anti-IgE to produce an immediate wheal of 10 mm compared to subjects who did not develop an LPR (p = 0.02), suggesting that the concentration of the stimulus injected is more important for the development of a LPR than the size of the immediate cutaneous response. Skin reactivity to codeine phosphate (a non-IgE-dependent secretogogue) was correlated with skin reactivity to anti-IgE (r = 0.47; p < 0.05), suggesting that in vivo skin mast cell degranulation is partially a function of mast cell releasability. No adverse reactions to intradermal injection of rabbit F(ab′)₂ antihuman IgE occurred, and no increase in serum IgG antibodies to rabbit gamma globulin could be detected 3 weeks after skin testing. Antihuman IgE is therefore a skin test reagent that can be safely used to evaluate skin mast cell degranulation and LPR in vivo in nonatopic individuals and in those subjects whose allergic sensitivities are unknown.