Macrophage subsets in mechanical brain injury (MBI) – A contribution to timing of MBI based on immunohistochemical methods: A pilot study

Abstract Cortical hemorrhages as a consequence of closed mechanical brain injury (MBI) trigger an inflammatory response including a distinct increase of macrophages. According to published data this reactive macrophage population is heterogenous as to their immunological properties. The expression of certain immunohistochemically detectable epitopes of macrophages, however, may correlate with the posttraumatic interval (PTI). In a pilot study, 50 selected cases of cortical hemorrhages with 1 min to 1.5 years PTI were examined by light microscopy and macrophages were labeled with CD68-, HLA-D-, HAM-56-, LN-5-, and 25F9-antibodies, while hemosiderin was detected by a Prussian-blue reaction. Qualitative and semiquantitative investigations were performed. The semiquantitative study included 5 different classes. The results of the study revealed a distinct timetable of the appearance of macrophages labeled with certain antibodies. While HLA-D immunoreactivity was detected after a PTI of 6h in the cortex and white matter bordering the traumatic hemorrhage, CD68 immunopositive macrophages were present after 12h, LN-5 and HAM-56 after 48h, and 25F9 within 10d. Hemosiderin-containing macrophages were detectable within 100h in the same region. Within the hemorrhage itself a certain immunoreactivity of macrophages starts several hours before: CD68 after 3h, LN-5 after 24h, HAM-56 after 31h, hemosiderin after 76h, and 25F9 after 4d. For forensic purposes these observations are of crucial importance because the time course of the appearance of certain immunopositive macrophages labeled with different antibodies allows a differentiated timing of contusional injuries; however, the cause of this different immunopositive reaction remains unexplained. The observed time dependency of different macrophage antigen expressions in cortical hemorrhages after closed head injury is a suitable method to estimate the PTI and will allow a forensic reliable estimation if future investigations are extended on higher numbers of cases and/or additional markers.