Toll-like receptor 4 and Syk kinase shape dendritic cell-induced immune activation to major house dust mite allergens

Stefanie Busold; Jaap H Akkerdaas; Esther M Zijlstra-Willems; Kees van der Graaf; Sander W Tas; Esther C de Jong; Ronald van Ree; Teunis B H Geijtenbeek

doi:10.3389/fmed.2023.1105538

Toll-like receptor 4 and Syk kinase shape dendritic cell-induced immune activation to major house dust mite allergens

Front Med (Lausanne). 2023 Aug 8:10:1105538. doi: 10.3389/fmed.2023.1105538. eCollection 2023.

Authors

Stefanie Busold^{1

2}, Jaap H Akkerdaas^{1

2}, Esther M Zijlstra-Willems^{1

2}, Kees van der Graaf³, Sander W Tas^{1

2

4}, Esther C de Jong^{1

2}, Ronald van Ree^{1

2

5}, Teunis B H Geijtenbeek^{1

2}

Affiliations

¹ Amsterdam University Medical Centers, location AMC, Department of Experimental Immunology, Amsterdam, Netherlands.
² Amsterdam Institute for Infection and Immunity, Inflammatory Diseases, Amsterdam, Netherlands.
³ Citeq Biologics, Groningen, Netherlands.
⁴ Amsterdam Rheumatology and Immunology Center, Department of Rheumatology and Clinical Immunology, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands.
⁵ Amsterdam University Medical Centers, location AMC, Department of Otorhinolaryngology, Amsterdam, Netherlands.

Abstract

Background: House dust mite (HDM) is a major cause of respiratory allergic diseases. Dendritic cells (DCs) play a central role in orchestrating adaptive allergic immune responses. However, it remains unclear how DCs become activated by HDM. Biochemical functions of the major HDM allergens Der p 1 (cysteine protease) and Der p 2 (MD2-mimick) have been implicated to contribute to DC activation.

Methods: We investigated the immune activating potential of HDM extract and its major allergens Der p 1 and Der p 2 using monocyte-derived DCs (moDCs). Maturation and activation markers were monitored by flow cytometry and cytokine production by ELISA. Allergen depletion and proteinase K digestion were used to investigate the involvement of proteins, and in particular of the major allergens. Inhibitors of spleen tyrosine kinase (Syk), Toll-like receptor 4 (TLR4) and of C-type lectin receptors (CLRs) were used to identify the involved receptors. The contribution of endotoxins in moDC activation was assessed by their removal from HDM extract.

Results: HDM extract induced DC maturation and cytokine responses in contrast to the natural purified major allergens Der p 1 and Der p 2. Proteinase K digestion and removal of Der p 1 or Der p 2 did not alter the immune stimulatory capacity of HDM extract. Antibodies against the CLRs Dectin-1, Dectin-2, and DC-SIGN did not affect cytokine responses. In contrast, Syk inhibition partially reduced IL-6, IL-12 and completely blocked IL-10. Blocking TLR4 signaling reduced the HDM-induced IL-10 and IL-12p70 induction, but not IL-6, while endotoxin removal potently abolished the induced cytokine response.

Conclusion: Our data strongly suggest that HDM-induced DC activation is neither dependent on Der p 1 nor Der p 2, but depend on Syk and TLR4 activation, which might suggest a crosstalk between Syk and TLR4 pathways. Our data highlight that endotoxins play a potent role in immune responses targeting HDM.

Keywords: Der p 1; Der p 2; Syk; TLR4; dendritic cell activation; house dust mite allergy.