ENTRY OF MONOCYTES INTO THE BRAIN AFTER INJECTION OF CORYNEBACTERIUM-PARVUM

The receptiveness of the brain to monocyte infiltration was studied in rats that had been injected intracerebrally with Corynebacterium parv um. At 0-17 days after intracerebral injection and 18 h after intraven ous injection of diI-labeled isogenous mononuclear cells, host rats we re sacrificed and cells from the vicinity of the injection site and fr om the contralateral cerebral hemisphere were dissociated and analyzed by flow cytometry. In rats sacrificed 4-11 days postinjection of C. p arvum, diI-labeled mononuclear cells were detected in cell preparation s from the hemisphere ipsilateral and, to a lesser extent, contralater al to the injection site, No extravasation of cells from the blood to the brain was detected in rats injected intracerebrally with saline. B y immunohistochemistry, many macrophages were detected in the hemisphe re ipsilateral to injection of C. parvum. In additional experiments, t he dissociated CNS cell population was labeled with OX-42 antibodies t o the type 3 complement receptor which is present on monocytes but not lymphocytes. Some cells in the brain were labeled with both diI and O X-42 and therefore were identified as monocytes that had entered the b rain from the blood, In conclusion, monocytes can home to both sides o f the brain after unilateral injection of a strong inflammatory agent but monocyte infiltration into the brain is delayed in comparison to m onocyte inflammatory responses that have been reported in nonneural ti ssues. (C) 1998 Academic Press.