PCNA and psoriasis: Moreover, both topical and intraperitoneal administration of montelukast suppressed the mRNA levels of various cytokines (IL-12A, IL-17A/F, and IL-23), markers of keratinocyte proliferation (KI67, PCNA) 30, and genes associated with autoimmunity (LL37) 31 in skin lesions and played a role in regulating disease progression in the context of psoriasis 32.