Urquizu-Padilla M, Balada E, Cortés F, Pérez EH, Vilardell-Tarrés M, Ordi-Ros J. Serum levels of soluble CD40 ligand at flare and at remission in patients with systemic lupus erythematosus. J Rheumatol. 2009 May;36(5):953–60. doi: 10.3899/jrheum.080978. PMID: 19332622.