Cytokine that binds to TNFRSF4. Co-stimulates T-cell proliferation and cytokine production. Homotrimer. By HTLV-1 transactivator p40-Tax. Disease susceptibility is associated with variants affecting the gene represented in this entry. The upstream region of TNFSF4 contains a single risk haplotype for SLE, which is correlated with increased expression of both cell-surface TNFSF4 and TNFSF4 transcripts. Increased levels of TNFSF4 are thought to augment T-cell-APC interaction and the functional consequences of T-cell activation, thereby destabilizing peripheral tolerance. Belongs to the tumor necrosis factor family.