SEL1L3 (SEL1L family member 3) is a previously uncharacterized protein encoded on chromosome 4 that plays multifaceted roles in cellular stress regulation and immune-related processes. Mechanistically, SEL1L3 regulates endoplasmic reticulum (ER) stress response pathways, as demonstrated by ER stress activation following SEL1L3 silencing in lung adenocarcinoma cells 1. The protein undergoes hyper-N-glycosylation modifications, particularly at amino acid position 527, which influences its immunogenic properties and B-cell receptor recognition 2. SEL1L3 demonstrates significant disease relevance across multiple malignancies and vascular pathology. It functions as a senescence-associated biomarker in atherosclerosis, correlating with immune cell infiltration and macrophage differentiation patterns 3. As a B-cell marker gene, SEL1L3 is associated with prognosis and immunotherapy response in triple-negative breast cancer 4. In lung adenocarcinoma, elevated SEL1L3 expression correlates with better clinical outcomes and favorable immune phenotypes 1. SEL1L3 also serves as a core gene linking renal clear cell carcinoma and atherosclerosis, with lower expression predicting worse prognosis 5. In glioblastoma, SEL1L3 is part of a validated six-gene prognostic model 6, and it represents a potential tumor antigen for mRNA vaccine development in melanoma 7. Clinically, SEL1L3 emerges as a promising biomarker for disease surveillance, risk stratification, and immunotherapy response prediction across multiple cancer types and atherosclerosis.