Production of macrophage inflammatory protein‐2 following hypoxia/reoxygenation in glial cells

Polymorphonuclear neutrophils (PMNs) are known to mediate brain inflammation following hypoxia/reoxygenation (H/R), but the precise mechanisms leading to PMN recruitment are undefined. The α‐chemokine macrophage inflammatory protein‐2 (MIP‐2) has specificity for the recruitment of PMNs. In this study, we found that 8 or 12 h of hypoxia followed by 24‐h reoxygenation (H8/R24 or H12/R24) induced MIP‐2 secretion in cultures of enriched microglia or mixed glia, respectively. Microglia, however, could not survive longer duration (>12 h) of hypoxia. Astrocytes did not produce any significant amount of MIP‐2 even though astrocytes maintained 98–99% viability following H12/R24. We also found that microglia survived the H/R treatment better (following H24) in the presence of astrocytes (mixed glial culture) than in microglia‐enriched culture. Reoxygenation for prolonged periods (3 and 5 days) following H24 resulted in progressively larger increases in MIP‐2 production (20‐ and 60‐fold, respectively) in mixed glial cultures. Immunocytochemical staining revealed that the cells expressing MIP‐2 in response to H/R were microglia rather than astrocytes in mixed glial cultures. Examination of MIP‐2 mRNA expression showed that H/R upregulated MIP‐2 gene expression. Taken together, our data suggest that microglial cells are an important source of MIP‐2 production and suggest a potential injury mechanism involving brain‐derived production of MIP‐2 in H/R. GLIA 32:155–164, 2000. © 2000 Wiley‐Liss, Inc.