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Antibodies against Mac-1 attenuate neutrophil accumulation after traumatic brain injury in rats
R S Clark1, T M Carlos, J K Schiding
1Department of Anesthesiology and Critical Care Medicine, Safar Center for Resuscitation Research, University of Pittsburgh, Pennsylvania 15260, USA.
Abstract:
Neutrophils (PMN) accumulate and are associated with cerebrovascular disturbances after experimental traumatic or ischemic brain injury, and meningitis. We hypothesized that posttraumatic PMN accumulation in brain is mediated by the PMN adhesion receptor Mac-1 (CD11b/CD18). Anesthetized rats were randomized to receive 2 mg/kg intravenously of murine monoclonal antibody to rat Mac-1 (1-B6) or anti-Mac-1 F(ab)2' [1-B6F(ab)2'] fragment (Repligen Corp., Cambridge, MA). Control rats were treated with isotype matched control antibody. Rats were subjected to percussive trauma to the right parietal cortex 30 min after treatment. Rats were killed 24 h posttrauma, and PMN accumulation was assessed by myeloperoxidase (MPO) activity. The presence of 1-B6F(ab)2' bound to PMN in brain after trauma was assessed by immunohistochemistry. Complete blood cell counts were obtained before treatment and 24 h after trauma. Brain MPO activity was reduced by 43% in the 1-B6-treated rats vs. controls (0.31 +/- 0.09 vs 0.55 +/- 0.10 U/g, n = 6/group, p = 0.013) and by 34% in the 1-B6F(ab)2'-treated rats vs. controls (0.43 +/- 0.10 vs. 0.65 +/- 0.09 U/g, n = 6/group, p = 0.006). Systemic neutropenia developed in the 1-B6-treated rats (absolute PMN count decreased by 73% vs. baseline) but not in rats treated with 1-B6F(ab)2' (absolute PMN count increased by 26 and 25% vs. baseline in treated and controls, respectively). Immunohistochemical staining showed 1-B6F(ab)2' on the surface of infiltrated PMN 24 h after trauma. Mac-1 mediates posttraumatic PMN accumulation in brain. This accumulation can be attenuated by 34%, without reducing circulating PMN, using an anti-Mac-1 F(ab)2' fragment; however, some PMN coated with 1-B6F(ab)2' still infiltrate into traumatized tissue. These results are similar to those reported in models of cerebral ischemia, and suggest the participation of multiple PMN adhesion pathways after ischemic and traumatic brain injury.
Insights
Neutrophil accumulation in the brain after injury is mediated by Mac-1. Targeting Mac-1 with an antibody fragment reduced this accumulation by 34% without causing systemic neutropenia.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Neutrophils (PMN) infiltrate the brain following traumatic or ischemic injury and meningitis, contributing to cerebrovascular disturbances.
- The adhesion receptor Mac-1 (CD11b/CD18) on PMNs is a potential mediator of this post-injury accumulation.
Purpose of the Study:
- To investigate the role of Mac-1 in mediating posttraumatic PMN accumulation in the brain.
- To evaluate the efficacy of an anti-Mac-1 antibody fragment in attenuating this accumulation.
Main Methods:
- Rats were treated with a monoclonal antibody to rat Mac-1 (1-B6) or its F(ab)2' fragment (1-B6F(ab)2'), or an isotype control antibody.
- Percussive cortical trauma was induced 30 minutes post-treatment.
- PMN accumulation was quantified by myeloperoxidase (MPO) activity 24 hours post-trauma.
- Complete blood counts and immunohistochemistry were used to assess systemic PMN levels and antibody binding.
Main Results:
- Brain MPO activity was significantly reduced by 43% in rats treated with 1-B6 and 34% in rats treated with 1-B6F(ab)2' compared to controls.
- Systemic neutropenia occurred with 1-B6 treatment, but not with 1-B6F(ab)2' treatment.
- Immunohistochemistry confirmed the presence of 1-B6F(ab)2' on infiltrated PMNs in the traumatized brain tissue.
Conclusions:
- Mac-1 plays a critical role in mediating posttraumatic PMN accumulation in the brain.
- Anti-Mac-1 F(ab)2' fragments can attenuate PMN brain infiltration by 34% without causing systemic neutropenia.
- These findings suggest potential therapeutic strategies for brain injury, highlighting the involvement of multiple PMN adhesion pathways.