Pathways of immediate hypothermia and leukocyte infiltration in an adjuvant-free mouse model of anaphylaxis

Abstract

Background Conflicting results have been obtained regarding roles of Fc receptors and effector cells in models of active systemic anaphylaxis (ASA). In part, this might reflect the choice of adjuvant used during sensitization, as various adjuvants might differentially influence the production of particular antibody isotypes. Objective We developed an ‘adjuvant-free’ mouse model of ASA and assessed the contributions of components of the ‘classical’ and ‘alternative’ pathways in this model. Methods Mice were sensitized intra-peritoneally (i.p.) with ovalbumin at weekly intervals for 6 weeks and challenged i.p. with ovalbumin two weeks later. Results Wild-type animals developed immediate hypothermia and late-phase intra-peritoneal inflammation in this model. These features were reduced in mice lacking the IgE receptor FcεRI, the IgG receptor FcγRIII or the common γ-chain FcRγ. FcγRIV blockade resulted in a partial reduction of inflammation without any effect on hypothermia. Depletion of monocytes/macrophages with clodronate liposomes significantly reduced the hypothermia response. By contrast, depletion of neutrophils or basophils had no significant effects in this ASA model. Both the hypothermia and inflammation were dependent on platelet-activating factor (PAF) and histamine and were reduced in two types of mast cell (MC)-deficient mice. Finally, engraftment of MC-deficient mice with bone marrow-derived cultured MCs significantly exacerbated the hypothermia response, and restored inflammation to levels similar to those observed in wild-type mice. Conclusion Components of the classical and alternative pathways contribute to anaphylaxis in this adjuvant-free model, with key roles for mast cells and monocytes/macrophages.

The pathophysiology of anaphylaxis

“…101 Studies in mice have shown that depletion of monocytes/macrophages using clodronate liposomes can reduce anaphylaxis in both IgG-mediated passive models and active models 52, 89, 92, 102, 103 (Table 1). These data suggest that monocytes/macrophages might play an important role in anaphylaxis.…”

“…52, 55 Antibody-mediated neutrophil depletion can reduce anaphylaxis in IgG-mediated PSA 52, 53, 56 and mast cell-independent ASA models. 53, 103 However, neutrophil-depleting antibodies had no effect in a mast cell-dependent ASA model induced without artificial adjuvants. 103 This suggests that neutrophils may be particularly prominent in ASA models induced with adjuvants and that such models may not require any non-redundant contributions of mast cells (Table 1).…”

“…In agreement with that, histamine release is abrogated in mast cell-deficient mice in a model of IgE-mediated PSA, 27 and increases in plasma histamine levels are also abrogated, in two models of ASA, in mice deficient for both mast cells and basophils. 91, 103 …”

“…Using an adjuvant-free active anaphylaxis model, we recently reported that the PAFR antagonist CV-6209 can reduce anaphylaxis in wild-type mice, but has no effect on the residual anaphylaxis observed in monocyte/macrophage-depleted mice, suggesting that monocytes/macrophages represent the major source of PAF in this model. 103 …”

Outstanding animal studies in allergy I. From asthma to food allergy and anaphylaxis

“…Knockout models indicated that the anaphylactic drop of body temperature depended on mouse FcεRI, FcγRIII and γ-chain FcRγ, whereas FcγRIV related to inflammation only [65 ▪ ]. In this model, macrophages and neutrophils turned out to be less important in anaphylaxis than mast cells.…”