Intravenous multipotent adult progenitor cell therapy after traumatic brain injury: modulation of the resident microglia population
- Equal contributors
1 Department of Surgery, University of Texas Medical School at Houston, 6431 Fannin Street, MSB 5.236, Houston, TX, 77030, USA
2 Pediatric Surgery, University of Texas Medical School at Houston, 6431 Fannin Street, MSB 5.236, Houston, TX, 77030, USA
3 Michael E DeBakey Institute for Comparative Cardiovascular Science and Biomedical Devices, Texas A & M University, College Station, TX, USA
4 Department of Regenerative Medicine, Athersys Inc, 3201 Carnegie Avenue, Cleveland, OH, 44115, USA
Journal of Neuroinflammation 2012, 9:228 doi:10.1186/1742-2094-9-228Published: 28 September 2012
We have demonstrated previously that the intravenous delivery of multipotent adult progenitor cells (MAPC) after traumatic brain injury affords neuroprotection via interaction with splenocytes, leading to an increase in systemic anti-inflammatory cytokines. We hypothesize that the observed modulation of the systemic inflammatory milieu is related to T regulatory cells and a subsequent increase in the locoregional neuroprotective M2 macrophage population.
C57B6 mice were injected with intravenous MAPC 2 and 24 hours after controlled cortical impact injury. Animals were euthanized 24, 48, 72, and 120 hours after injury. In vivo, the proportion of CD4+/CD25+/FOXP3+ T-regulatory cells were measured in the splenocyte population and plasma. In addition, the brain CD86+ M1 and CD206+ M2 macrophage populations were quantified. A series of in vitro co-cultures were completed to investigate the need for direct MAPC:splenocyte contact as well as the effect of MAPC therapy on M1 and M2 macrophage subtype apoptosis and proliferation.
Significant increases in the splenocyte and plasma T regulatory cell populations were observed with MAPC therapy at 24 and 48 hours, respectively. In addition, MAPC therapy was associated with an increase in the brain M2/M1 macrophage ratio at 24, 48 and 120 hours after cortical injury. In vitro cultures of activated microglia with supernatant derived from MAPC:splenocyte co-cultures also demonstrated an increase in the M2/M1 ratio. The observed changes were secondary to an increase in M1 macrophage apoptosis.
The data show that the intravenous delivery of MAPC after cortical injury results in increases in T regulatory cells in splenocytes and plasma with a concordant increase in the locoregional M2/M1 macrophage ratio. Direct contact between the MAPC and splenocytes is required to modulate activated microglia, adding further evidence to the central role of the spleen in MAPC-mediated neuroprotection.