Proton-coupled amino-acid transporter that transports free histidine and certain di- and tripeptides, and is involved in innate immune response (PubMed:39719710). Preferably binds to short peptides with a basic residue at the first position and a hydrophobic residue at the second position (PubMed:39719710). Also able to transport carnosine (PubMed:31073693, PubMed:31254495). 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 (By similarity). {ECO:0000250|UniProtKB:Q8BPX9, ECO:0000269|PubMed:31073693, ECO:0000269|PubMed:31254495, ECO:0000269|PubMed:39719710}. This is the function of SLC15A3 (solute carrier family 15 member 3, Ensembl gene identifier ENSG00000110446).