Lam, K.-P. | Search bioRxiv

bioRxiv2024

Gut microbiota-derived GlcNAc-MurNAc is a TLR4 agonist that protects the host gut

Gut microbiota-derived peptidoglycan fragments (PGNs) are key signaling molecules that regulate multiple aspects of the hosts health. Yet the exact structures of natural PGNs in hosts have not been fully elucidated. Herein, we developed an LC-HRMS/MS analytical platform for global quantification and profiling of natural PGN subtypes in host gut and sera, unexpectedly revealing the abundance of PGN-derived saccharide moieties that do not resemble canonical ligands of mammalian NOD1/2 receptors. Focusing on the disaccharide GlcNAc-MurNAc (GM), a natural gut PGN that does not activate NOD1/2 yet still exhibits robust immunostimulatory effects in host immune cells, we unambiguously established GM as a TLR4 agonist, adding to the growing knowledge of NOD-independent mechanisms of PGN sensing in hosts. Importantly, the administration of GM effectively mitigates colonic inflammation in the DSS-induced colitis model in mice via TLR4-dependent mechanisms, highlighting the in vivo significance of natural gut microbiota-derived PGNs in maintaining host intestinal homeostasis.

biochemistry↗

bioRxiv2024

Enhanced NK cell proficiency in solid tumors through antigen-specific memory via NKG2C/A-HLA-E/ABC recruited to tumors by CXCR2

Natural killer (NK) cells have emerged as promising effectors in cancer immunotherapy due to their ability to recognize and eliminate tumor cells. To investigate the immunological memory and tumor reactivity of adaptive (a)NK cells in the context of desmoplastic tumors, we used human ovarian cancer as a model. Through in vitro culture systems resembling dendritic cell (DC)-mediated T cell activation, we demonstrated that aNK cells exhibit antigen-specific cytotoxic responses and memory generation towards ovarian tumor antigens. Furthermore, mature DCs presenting tumor-associated antigens induced the expansion of aNK cells, suggesting antigen-specific proliferation. Single-cell transcriptomics revealed a distinct genetic signature of aNK cells in tumor samples, characterized by a cytotoxic phenotype and interactions with myeloid cells, particularly DCs. The spatial analysis confirmed the intratumoral presence of aNK cells, with higher abundance in the tumor nest compared to conventional (c)NK cells. Functional assays demonstrated the cytotoxicity of expanded aNK cells against autologous ovarian tumors, accompanied by an activated receptor profile. Importantly, aNK cells displayed antigen-specific memory responses towards primary tumors, maintaining specificity over time. Blockade of NKG2C and HLA-E influenced aNK cell recall responses, indicating their roles in the adaptive NK cell immune memory. Additionally, CXCR2 was essential for efficient aNK cell migration toward tumors. These findings shed light on the therapeutic potential of aNK cells in ovarian cancer immunotherapy, highlighting their ability to develop immunological memory and effectively eradicate tumor cells.

immunology↗