Immune system modulation in the brain injury of the metallothionein-I/II null mutant mouse

Metallothionein-I/II (MT-I/II) is a 6-7 kDa, cysteine rich, zinc and copper binding protein. MT-I/II null mutant (\(^{−/−}\)) mice have an altered response to brain injury. Therefore, MT-I/II has been proposed to be a protective protein after brain injury but the mechanism by which it confers protection remains elusive. There is a possibility that MT-I/II has protective actions within the injured brain but MT-I/II also has the capacity to modulate the immune system which plays a role in the progression of brain injury. The aim of this thesis is to investigate the differences in the progression of brain injury between wild type and MT-I/II\(^{−/−}\) mice with particular emphasis on the action of MT-I/II in organs peripheral to the central nervous system after brain injury. Using a cryolesion brain injury model, neuron death in MT-I/II\(^{−/−}\) mice was prolonged at later stages of the brain injury (7 days post-injury) meanwhile it had ceased in wild type mice. In conjunction with this occurrence, the numbers of T cells infiltrating the injury site were significantly higher in MT-I/II\(^{−/−}\) mice at 7 days post-injury. Chemokine mRNA synthesis was analysed to determine if MT-I/II\(^{−/−}\) mice had altered chemotactic signals that may affect the rate of T cell infiltration but differences were rarely observed when compared to wild type mice. In MT-I/II\(^{−/−}\) mice, circulating leukocytes showed no differences to wild type mice in the relative ratios of lymphocytes, neutrophils, monocytes or T cells. However, the absolute white blood cell count was significantly higher in the blood of MT-I/II\(^{−/−}\) mice, but only at 7 days post-injury. MT-I/II\(^{−/−}\) mice were also found to have lower levels of the marker of alternatively activated macrophages, Ym1, than wild type mice, both in macrophages in the brain and in monocytes in the blood after brain injury. Therefore, there appear to be several immune system differences between MT-I/II\(^{−/−}\) mice and wild type mice after brain injury. To further investigate the role of MT-I/II after brain injury, MT-I and MT-II mRNA levels were quantified by reverse transcriptase PCR. An enzyme-linked immunoassay (ELISA) was developed to measure MT-I/II protein levels in brain and liver after brain injury. Both MT-I and MT-II mRNA levels increase at 1 day post-injury in brain and liver and are decreased by 7 days post-injury. MT-I/II protein in brain was highest at 1 day post-injury but in the liver was maximally expressed at 7 days post injury. This increase in hepatic MT-I/II protein resulted in a higher hepatic zinc content in wild type mice compared to MT-I/II\(^{−/−}\) mice. Therefore these results suggest that brain injury induces a hepatic MT-I/II response which may be responsible for modulation of the essential trace metal, zinc after brain injury