‘Yin and Yang’ in inflammation: duality in innate immune cell function and tumorigenesis

BACKGROUND: The two stages of the acute inflammatory process are apoptosis ('Yin') and wound healing or resolution ('Yang'). Inflammation defends the host against unwanted elements. OBJECTIVE/METHODS: To present a discussion of pleiotropic roles of innate immune cells possessing 'tumoricidal' and/or 'tumorigenic' properties in inflammation-induced dysfunction of the immune system and the genesis of chronic inflammatory diseases, hyperplasia, precancer/neoplasia or tumor and angiogenesis. RESULTS/CONCLUSIONS: Loss of maintenance of the balance between apoptosis and wound healing and co-existence of death and growth factors in tissues could create 'immunological chaos' with accumulation of 'immune response mismatches'. Unresolved inflammation plays a role in the genesis of chronic inflammatory and autoimmune diseases and cancer. Identification of accumulated 'mismatched' death and growth factors during the developmental phases of immune dysfunction in target tissues or cancer microenvironment presents challenges and opportunities for future studies on diagnosis, prevention and therapy of these diseases.