Proton-coupled amino-acid transporter that mediates the transmembrane transport of L-histidine and some di- and tripeptides from inside the lysosome to the cytosol, and plays a key role in innate immune response (PubMed:19570976, PubMed:21277849, PubMed:25238095, PubMed:27845049, PubMed:29305823). Able to transport a variety of di- and tripeptides, including carnosine and some peptidoglycans (PubMed:29784761). Transporter activity is pH-dependent and maximized in the acidic lysosomal environment (By similarity). Involved in the detection of microbial pathogens by toll-like receptors (TLRs) and NOD-like receptors (NLRs), probably by mediating transport of bacterial peptidoglycans across the endolysosomal membrane: catalyzes the transport of certain bacterial peptidoglycans, such as muramyl dipeptide (MDP), the NOD2 ligand, and L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate (tri-DAP), the NOD1 ligand (PubMed:19570976, PubMed:23028315, PubMed:25238095, PubMed:24695226, PubMed:29784761). Required for TLR7, TLR8 and TLR9-mediated type I interferon (IFN-I) productions in plasmacytoid dendritic cells (pDCs) (PubMed:21045126, PubMed:23382217, PubMed:25238095, PubMed:30262916). Independently of its transporter activity, also promotes the recruitment of innate immune adapter TASL to endolysosome downstream of TLR7, TLR8 and TLR9: TASL recruitment leads to the specific recruitment and activation of IRF5 (By similarity). Required for isotype class switch recombination to IgG2c isotype in response to TLR9 stimulation (PubMed:25310967). Required for mast cell secretory-granule homeostasis by limiting mast cell functions and inflammatory responses (PubMed:29155995). H(+)(out) + L-histidine(out) = H(+)(in) + L-histidine(in) a dipeptide(out) + H(+)(out) = a dipeptide(in) + H(+)(in) an L-amino acid tripeptide(out) + H(+)(out) = an L-amino acid tripeptide(in) + H(+)(in) H(+)(out) + N-acetylmuramyl-L-alanyl-D-isoglutamine(out) = H(+)(in) + N-acetylmuramyl-L-alanyl-D-isoglutamine(in) H(+)(out) + L-alanyl-gamma-D-glutamyl-meso-diaminoheptanedioate(out) = H(+)(in) + L-alanyl-gamma-D-glutamyl-meso-diaminoheptanedioate(in) glycyl-sarcosine(out) + H(+)(out) = glycyl-sarcosine(in) + H(+)(in) carnosine(out) + H(+)(out) = carnosine(in) + H(+)(in) Interacts with TASL; leading to TASL recruitment to endolysosome. Preferentially expressed in immune tissues, including B-cells and dendritic cells (PubMed:21277849). Highly expressed in macrophages (PubMed:29784761). Mice are fertile and look healthy but display impaired cytokine production in dendritic cells (PubMed:21277849). Reduced uptake of L-histidine in brain (PubMed:27845049). Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family.