The temporo-spatial localization of polymorphonuclear cells related to the neurovascular unit after transient focal cerebral ischemia

Abstract

Inflammatory responses after cerebral ischemia are important for the development of final infarct size but the role of polymorphonuclear cells (PMN) is still a matter of debate, since previously used antibodies were recently declared as non-specific. In the present study, we investigated the temporo-spatial localization of PMN related to the neurovascular unit using specific antibodies, 7/4 and Ly6G, and application of G-CSF to induce proliferation and mobilization of PMN precursors after transient focal cerebral ischemia in mice. Infarct volumes, sensorimotor function, neurological outcome and immunohistochemical analysis of PMN were performed after G-CSF administration or placebo treatment. G-CSF-treated mice showed reduced infarct size (51.15±15.68mm2 vs. 39.31±16.13mm2 at day 1; 50.11±16.68mm2 vs. 33.16±4.86mm2 at day 4; p<0.05). They showed improved motor-function recovery and had a significantly better outcome compared to placebo-treated animals. Comparison of the two PMN detecting antibodies showed no difference in saturation plots or cell quantification. Studying the basement membrane-associated localization revealed ca. 60% extravascular PMN, independent of G-CSF administration. Extravascular PMNs were without any connection to laminin, but all near to the vessels. We conclude that 7/4 is a suitable marker to investigate PMN compared to Ly6G, which confirms results from former studies using the 7/4-antibody. Furthermore we report the observation that PMN were detected outside the laminin barrier but almost exclusively in close vicinity to the neurovascular unit.