IGHE and anaphylaxis: Furthermore, the reasons for increased toxicity of CPDI-02 in female vs. male outbred CD-1 mice after IM administration remain unclear but, given the role of mast cells (C5aR1-bearing cells [51]) in IgE-dependent and IgE-independent anaphylaxis [52], it might be related to sex-based differences in mast cell numbers and mast cell activation by CPDI-02 [53].