CD4 and erythema multiforme: Various studies have established that the immune system plays a major role in the pathophysiology and symptomatology of EM, and immune cells, including natural killer (NK) cells, macrophages, neutrophils, and the CD4 T helper cell system, are dysregulated in women with EM (Beste et al., 2014; Jeung et al., 2016; Patel et al., 2018; Zondervan et al., 2018).