RINL (Ras and Rab interactor like) is a guanine nucleotide exchange factor (GEF) that activates RAB5A and RAB22A by catalyzing GDP-to-GTP exchange 1. The protein localizes to cytosolic compartments and associates with the cytoskeleton, positioning it to spatially control Rab signaling at actin-positive structures 1. RINL regulates fluid-phase and EGFR endocytosis, with notably higher catalytic activity toward RAB22A than RAB5A 1. Beyond endocytosis, RINL functions as a negative regulator of T follicular helper (Tfh) cell differentiation through its GEF-dependent activity and regulation of CD28 internalization and signaling in CD4+ T cells 2. Loss of RINL increases Tfh generation in aging, immunization, and viral infection models across species 2. Additionally, RINL interacts with the protein odin and participates in EphA8 receptor degradation pathways via its Rab5-GEF activity 3. Recent epigenomic analyses implicate RINL in cardiovascular responses to environmental particulate matter exposure, suggesting potential relevance to environmental health 4. These findings establish RINL as a multifunctional regulator linking endocytic trafficking to immune cell differentiation and potentially environmental disease susceptibility.