CD40LG and oral lichen planus: A comprehensive search was done in four databases, including PubMed/Medline, Scopus, Web of Science, Cochrane Library as well as Iranian databases with key terms (“oral lichen planus” or “OLP”), (“immunoglobulin”, “IgA”, “IgG”, or “IgM”), and (“saliva”, “salivary, or “serum”) up to January 2018, without language restriction.