Intracutaneous test with penicillin after priming of the skin with autologous serum containing specific IgE to penicillin

Background: Only a minority of patients allergic to penicillin having specific IgE against penicillin also present with a positive intracutaneous test (ICT) to penicillin and vice versa. This is in contrast to what we see in patients sensitized to classic type 1 allergens, e.g. grass or peanuts. A hypothesis could be that specific IgE against penicillin measured in serum is not present or active in the skin. The aim of this study was to investigate if you by priming the skin with autologous serum in patients with specific IgE to penicillin subsequently can elicit a positive ICT upon skin testing. Method: Ten patients with measurable levels of specific IgE to penicillin (mean 2.87, range 0.38-20.0) were included. On day 1, 0.1 ml autologous serum was injected intracutaneously on the volar forearm at 3-4 places. The autologous serum used was either freshly drawn (n = 2), or in cases where the present level of IgE to penicillin was low (mean 3.23, range 0.92- 20.00), priming was performed with serum containing higher levels of specific IgE to penicillin (mean 6.5, range 0.38-28.8), stored in the Center's serum bank. On day 2, ICT and skin microdialysis was performed, as described by Jelstrup Petersen, in both primed and non-primed areas. Histamine was measured at baseline and after ICT (0.05 ml) with penicillin, where after residual histamine from skin mast cells was released by injection of codeine (0.05 ml). Histamine in the eluate was subsequently analyzed by fluorescence spectroscopy using the microtiter method developed by Skov. Results: Eight/10 were primed with serum from the serum bank, and two with freshly drawn serum. Two/10 had a positive ICT in non-primed skin, the rest were ICT negative. ICT performed in the primed areas did not result in any further positive ICTs. In the positive ICTs no histamine was detected. All patients released significant amounts of histamine upon ICT with codeine. Conclusion: Our data do not support the hypothesis that the presence of IgE against penicillin and negative ICT is due to lack of specific IgE in the skin. Possible other explanations include presence of non-functional specific IgE to penicillin or that a positive ICT is not IgE mediated.