Ontogeny of inter‐alpha inhibitor protein (IAIP) expression in human brain

Inter‐alpha inhibitor proteins (IAIPs) are naturally occurring immunomodulatory molecules found in most tissues. We have reported ontogenic changes in the expression of IAIPs in brain during development in sheep and abundant expression of IAIPs in fetal and neonatal rodent brain in a variety of cellular types and brain regions. Although a few studies identified bikunin, light chain of IAIPs, in adult human brain, the presence of the complete endogenous IAIP protein complex has not been reported in human brain. In this study, we examined the immunohistochemical expression of endogenous IAIPs in human cerebral cortex from early in development through the neonatal period and in adults using well‐preserved postmortem brains. We examined total, nuclear, and cytoplasmic staining of endogenous IAIPs and their expression in neurofilament light polypeptide–positive neurons and glial fibrillary acidic protein (GFAP)–positive astrocytes. IAIPs were ubiquitously detected for the first time in cerebral cortical cells at 24–26, 27–28, 29–36, and 37–40 weeks of gestation and in adults. Quantitative analyses revealed that IAIPs were predominately localized in the nucleus in all age groups, but cytoplasmic IAIP expression was more abundant in adult than in the younger ages. Immunoreactivity of IAIPs was expressed in neurons and astrocytes in all age groups. In addition, IAIP co‐localization with GFAP‐positive astrocytes was more abundant in adults than in the developing brain. We conclude that IAIPs exhibit ubiquitous expression, and co‐localize with neurons and astrocytes in the developing and adult human brain suggesting a potential role for IAIPs in development and endogenous neuroprotection. Inter‐alpha inhibitor proteins (IAIPS) are expressed in the nucleus and cytoplasm of neurons and astrocytes in the developing and adult human brain. Cytoplasmic IAIP expression is more abundant in the adult brain than in the brain of the younger age groups. IAIPs probably play a potential role in neonatal brain development and endogenous neuroprotection.