Die Rolle FcepsilonR1-interagierender Proteine für die Allergen/Antigenvermittelte Aktivierung von Mastzellen
Zusammenfassung der Projektergebnisse
The primary aim of this grant was the identification of novel FcεRI-interacting proteins and their analysis with respect to pro-allergic and pro-inflammatory mast cell functions. Using IgE as bait, the expopeptidase CD13 (aminopeptidase N) was detected by mass spectrometry and suggested to be functionally interacting with the FcεRI. This was confirmed by demonstrating antigen-triggered co-capping and co-internalization of the FcεRI and CD13 in different types of mast cells. Moreover, antibody-mediated crosslinking of CD13 resulted in production of the pro-inflammatory cytokine IL-6, which was dependent on expression of FcεRI on the mast cell surface. Though these data indicated functional interaction between the two surface receptors, FcεRI and CD13, they did not allow direct assignment of a positive or negative role to CD13 with respect to FcεRI signaling. Thus, we used CD13-deficient mice to differentiate bone marrow-derived mast cells (BMMCs) and analyze the effects of CD13 deficiency on FcεRI-dependent pro-inflammatory mast cell activation. CD13 deficiency had no effect on mast cell differentiation and proliferation, neither in vitro nor in vivo. Analysis of antigen-triggered degranulation as well as production and release of pro-inflammatory cytokines (IL-6 and TNF-α) in these cells revealed an inhibitory role of CD13 in the context of FcεRI-mediated mast cell activation.The inhibitory function of CD13 could be corroborated in vivo in a low-dose model of passive systemic anaphylaxis. Antigen-dependent decrease in body temperature, reflecting an anaphylactic reaction, was substantially enhanced in CD13-deficient mice. As well, treatment of wild-type mice with the CD13 inhibitor bestatin resulted in an augmented anaphylactic reaction. Since CD13 inhibitors are developed as chemotherapeutics for cancer treatment, certain hypersensitivity reactions might appear as side effects of such treatments. Interestingly, human CD13 has been demonstrated to serve as receptor for coronavirus 229E that is known to cause upper respiratory tract infections. Since viruses represent “evolutionary designed” multivalent antigens, coronavirus could bind to several CD13 molecules at a time and thereby crosslink and activate the CD13-interacting FcεRI. We used transgenic mice expressing human CD13 under the control of the murine CD13 promoter to differentiate BMMCs with the aim to treat them with coronavirus 229E and measure FcεRI-dependent MC activation. Unfortunately, the respective BMMCs were not expressing human CD13, but only murine CD13. Therefore, this road could not be followed any further. Nevertheless, the question as to whether human mast cells might be activated by coronavirus 229E by its binding to CD13 and crosslinking the FcεRI is a valid one and should be followed using human mast cells (either mast cell lines like LAD2 or primary mast cells such as dermal or gut mast cells).
