Identification of scavenger receptor B1 as the airway microfold cell receptor forMycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis (Mtb) can enter the body through multiple routes, 15 including via specialized transcytotic cells called microfold cells (M cell). However, the 16 mechanistic basis for M cell entry remains undefined. Here, we show that M cell transcytosis 17 depends on the Mtb Type VII secretion machine and its major virulence factor EsxA. We identify 18 scavenger receptor B1 (SR-B1) as an EsxA receptor on airway M cells. SR-B1 is required for Mtb 19 binding to and translocation across M cells in mouse and human tissue. Together, our data 20 demonstrate a previously undescribed role for Mtb EsxA in mucosal invasion and identify SR-B1 21 as the airway M cell receptor for Mtb. 22 65 receptor class B type I (SR-B1). SR-B1 is enriched on mouse and human M cells both in vitro and 66 in vivo. Loss of SR-B1 reduces EsxA and Mtb binding to M cells, and prevents Mtb translocation 67 109 HBE/Raji B transwells, we observed that Mtb translocated across Caco-2/Raji B transwells in a 110 T7SS dependent manner (Fig. 1G). Taken together, these data show that the Mtb T7SS is necessary 111 for both binding to and translocation across M cells in vitro. 112 EsxA is sufficient to mediate binding to and translocation across M cells in vitro 113 Scavenger receptor class B type 1 binds EsxA and is expressed on M cells in vitro131 Because EsxA bound directly to the surface of M cells, we hypothesized that EsxA may 132 engage a cell surface receptor. To affinity purify cell surface binding proteins we performed a 133 modified co-immunoprecipitation experiment using either EsxA or transferrin crosslinked to the 134 TriCEPS reagent, a molecule that allows for the covalent cross-linking of a ligand and its receptor 135 157