Introduction Severe cerebral intraventricular haemorrhage (IVH) in preterm infants continues to be a major clinical problem. To date, no available therapy prevents infants from neurologic sequel following IVH. Recruitment of monocytes-macrophages and periventricular infiltration is a key step in the inflammatory response leading to brain damage. The sequence of the recruitment and profiling of monocytes-macrophages following IVH is not well characterised. We have previously shown that extracellular haemoglobin induces chemotactic cytokines following IVH. Haptoglobin is a haemoglobin scavenger and could potentially protect the immature brain from the detrimental effects of haemoglobin.
Objective To characterise the recruitment and differentiation of monocytes-macrophages in the intraventricular space following IVH and to investigate if haemoglobin scavenging with haptoglobin alters the recruitment and differentiation.
Methods Using a preterm rabbit pup model of IVH we characterised the immune cell recruitment and differentiation in intraventricular cerebrospinal fluid (CSF) at 24 to 72 h following haemorrhage. Using flow cytometry, immunohistochemistry and mRNA and protein analysis we characterised the systemic and CSF infiltrating macrophages in animals with IVH, sham controls and animals treated with intraventricular injections of haptoglobin.
Results Following IVH, there is an infiltration of M1 macrophages into the intraventricular CSF. Intraventricular introduction of the haemoglobin-scavenger haptoglobin modifies them into alternative M2 macrophages, expressing CD163. This causes a subsequent in vivo clearance of the accumulated haemoglobin.
Conclusion Following IVH, intraventricular haptoglobin treatment modifies macrophage differentiation, initiating clearance of extracellular haemoglobin. Treatment of haptoglobin might be a feasible approach to protect the immature brain following IVH.