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Histamine, leukotriene C4, IL-4, and IL-13 are major mediators of allergy and asthma. They are all formed by basophils and are released in particularly large quantities after stimulation with IL-3. Here we show that supernatants of activated mast cells or IL-3 qualitatively change the makeup of granules of human basophils by inducing de novo synthesis of granzyme B (GzmB), without induction of other granule proteins expressed by cytotoxic lymphocytes (granzyme A, perforin). This bioactivity of IL-3 is not shared by other cytokines known to regulate the function of basophils or lymphocytes. The IL-3 effect is restricted to basophil granulocytes as no constitutive or inducible expression of GzmB is detected in eosinophils or neutrophils. GzmB is induced within 6 to 24 hours, sorted into the granule compartment, and released by exocytosis upon IgE-dependent and -independent activation. In vitro, there is a close parallelism between GzmB, IL-13, and leukotriene C4 production. In vivo, granzyme B, but not the lymphoid granule marker granzyme A, is released 18 hours after allergen challenge of asthmatic patients in strong correlation with interleukin-13. Our study demonstrates an unexpected plasticity of the granule composition of mature basophils and suggests a role of granzyme B as a novel mediator of allergic diseases.

Summary Background: Various investigators have observed significant effects of highly diluted histamine on human basophil degranulation in vitro, compared to corresponding water controls. However, active and inactive dilution levels differed in most studies. Objective: We aimed to reproduce former studies with flow-cytometry usingrig orously controlled experimental conditions to minimise confoundingfactors. Methods: In seven independent experiments, basophils of the same human donor were incubated with diluted histamine (up to 10 −34 M) or water controls and activated with anti-IgE antibodies. Basophil activation was determined by using bicolour flow-cytometry. Experiments were blinded and performed with a randomised arrangement of the solutions on microtiter-plates. Results: Histamine at the dilutions 10 −2 M and 10 −22 M was associated with a significant inhibition of basophil degranulation (p = 0.018, Wilcoxon signed rank test) of 23.1% and 5.7%, respectively, if compared to ‘‘diluted’’ water treated in an identical manner. However, if all controls were pooled, only histamine 10 −2 M had a significant effect. Significant effects were seen for row numbers of the microtiter plates. Conclusion: We were not able to confirm the previously reported large effects of homeopathic histamine dilutions on basophil function of the examined donor. Seemingly, minor variables of the experimental set up can lead to significant differences of the results if not properly controlled. © 2005 Elsevier Ltd. All rights reserved.