Interleukin-4-induced protein 1 (IL4I1)

Interleukin-4-induced protein 1 (IL4I1) is a secreted L-amino acid oxidase that preferentially catalyzes the oxidative deamination of L-phenylalanine and, to a lesser extent, L-arginine and other aromatic amino acids[1][4]. Induced by interleukin-4, IL4I1 is expressed predominantly by antigen-presenting cells such as dendritic cells, macrophages, and some B cells, as well as in tumor-associated macrophages[1][2]. IL4I1 plays a central role in immune regulation by suppressing T-cell proliferation, promoting regulatory T-cell (Treg) differentiation, and limiting Th1 and Th17 responses[1][2][3][4]. It has immunosuppressive properties, which enable tumors to evade immune surveillance and promotes tumor progression, positioning it as a potential therapeutic target, particularly in cancer immunotherapy[2][3]. Mechanistically, IL4I1 exerts these effects through the generation of keto-acids such as indole-3-pyruvate and 4-hydroxy-phenylpyruvate, which can activate anti-oxidative and anti-ferroptotic pathways, and via production of hydrogen peroxide (H₂O₂) and ammonium (NH₄⁺), contributing to its antibacterial and immune-modulatory actions[3][4]. Disease associations include various cancers (notably B-cell lymphomas), infections, and possible neurodegenerative disorders[1][2]. Therapeutic targeting is an area of active research, but no approved drugs specifically inhibit IL4I1 as of now [2][3].

Other names

L-amino-acid oxidaseLAAOLAOFIG1Protein Fig-1IL4-induced protein 1hIL4I1hFIG1Interleukin-4-induced gene 1L-phenylalanine oxidaseInterleukin four induced 1UNQ636/PRO1265

Enzyme inhibition (e.g., targeting the L-amino acid oxidase activity of IL4I1) Immune checkpoint modulation (via T-cell suppression in the tumor microenvironment)