Hypoxic-ischemic encephalopathy (HIE) is a clinical condition in the neonate, resulting from
oxygen deprivation around the time of birth. HIE affects 1-5/1000 live births worldwide and is associated with the development of neurological deficits, including
cerebral palsy,
epilepsy, and cognitive disabilities. Even though the brain is considered as an immune-privileged site, it has innate and adaptive immune response and can produce
complement (C) components and
antimicrobial peptides (AMPs). Dysregulation of cerebral expression of AMPs and C can exacerbate or ameliorate the inflammatory response within the brain.
Brain ischemia triggers a prolonged inflammatory response affecting the progression of injury and secondary energy failure and involves both innate and adaptive immune systems, including immune-competent and non-competent cells. Following injury to the central nervous system (CNS), including neonatal
hypoxia-
ischemia (HI), resident microglia, and astroglia are the main cells providing immune defense to the brain in a stimulus-dependent manner. They can express and secrete pro-inflammatory
cytokines and therefore trigger prolonged
inflammation, resulting in neurodegeneration. Microglial cells express and release a wide range of
inflammation-associated molecules including several components of the
complement system. Complement activation following neonatal HI injury has been reported to contribute to neurodegeneration. Astrocytes can significantly affect the immune response of the CNS under pathological conditions through production and release of pro-inflammatory
cytokines and immunomodulatory AMPs. Astrocytes express β-
defensins, which can chemoattract and promote maturation of dendritic cells (DC), and can also limit
inflammation by controlling the viability of these same DC. This review will focus on the balance of
complement components and AMPs within the CNS following neonatal HI injury and the effect of that balance on the subsequent brain damage.