Hydroxychloroquine inhibits proteolytic processing of endogenous TLR7 protein in human primary plasmacytoid dendritic cells

• Published in: European journal of immunology Vol. 52; no. 1; pp. 54 - 61
• Main Authors: Cenac, Claire, Ducatez, Mariette, F., Guéry, Jean‐Charles
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.01.2022; Wiley-VCH Verlag
• Subjects: Acidification; Cell Line; COVID-19 - drug therapy; COVID-19 - immunology; Dendritic cells; Dendritic Cells - immunology; Endosomes - immunology; Humans; Hydroxychloroquine; Hydroxychloroquine - pharmacology; Immunology; Innate immunity to SARS‐CoV2; Leukemia; Life Sciences; Microbiology and Parasitology; Organelles; Pharmaceutical sciences; Pharmacology; Primary human pDCs; Processing of TLR7; Proteins; Proteolysis; Proteolysis - drug effects; SARS-CoV-2 - immunology; TLR7 protein; Toll-Like Receptor 7 - immunology; Toll-like receptors; Type I IFN; Virology; Hydroxychloroquine; Innate immunity to SARS-CoV2; Processing of TLR7; Primary human pDCs; Type I IFN
• ISSN: 0014-2980; 1521-4141
• DOI: 10.1002/eji.202149361

Toll‐like receptor 7 (TLR7) triggers antiviral immune responses through its capacity to recognize ssRNA. Proteolytic cleavage of TLR7 protein is required for its functional maturation in the endosomal compartment. Structural studies demonstrated that the N‐ and C‐terminal domains of TLR7 are connected and involved in ligand binding after cleavage. Hydroxychloroquine (HCQ), an antimalarial drug, has been studied for its antiviral effects. HCQ increases pH in acidic organelles and has been reported to potently inhibit endosomal TLR activation. Whether HCQ can prevent endogenous TLR7 cleavage in primary immune cells, such as plasmacytoid DCs (pDCs), had never been examined. Here, using a validated anti‐TLR7 antibody suitable for biochemical detection of native TLR7 protein, we show that HCQ treatment of fresh PBMCs, CAL‐1 leukemic, and primary human pDCs inhibits TLR7 cleavage and results in accumulation of full‐length protein. As a consequence, we observe an inhibition of pDC activation in response to TLR7 stimulation with synthetic ligands and viruses including inactivated SARS‐CoV2, which we show herein activates pDCs through TLR7‐signaling. Together, our finding suggests that the major pathway by which HCQ inhibits ssRNA sensing by pDCs may rely on its capacity to inhibit endosomal acidification and the functional maturation of TLR7 protein. TLR7 is an ssRNA sensor expressed in the endosomal compartment of pDCs and is essential for protective immunity against SARS‐CoV2. Here, we show that drugs that increase the pH of acidic organelles prevent TLR7 processing in primary human pDCs leading to defective TLR7 signaling and inhibition of type I IFN production in response to SARS‐CoV2.