CD4 and systemic lupus erythematosus: In this way, OX40 ligand (OX40-L)–OX40 axis has been identified as a key player in the increased Tfh responses (111): OX40-L, highly expressed by myeloid APCs in active SLE patients in response to TLR7 activation by RNP-anti-RNP immune complexes, promotes the differentiation of CD4+ T cells in functional Tfh cells (111).