The inclusion criteria for selecting the studies were: (i) detection of IgA, IgG and/or IgM levels in the serum and/saliva of OLP patients in case-control studies; (ii) the OLP diagnosis was in accordance with the clinical and/or histopathological WHO criteria [10]; (iii) healthy controls were reported and no other skin and/or systemic diseases affected OLP patients. The gene discussed is CD40LG; the disease is oral lichen planus.