The left and right neocortex of the brain has been shown to exert asymmetrical effects
on the immune system. In the present study, we used a middle cerebral artery (MCA)
occlusion model in Wistar rats to analyze the influence of unilateral CNS ischemia
on spleen cell number and function. The occlusion time was 1 h, followed by reperfusion
with survival for 0, 2, 7, 14, and 28 days. Changes in plasma norepinephrine levels
were used as an index of peripheral sympathetic activity. Results showed that the
total number of spleen cells significantly decreased after 2-28 days of survival in
animals with cerebral ischemia compared to sham-operated controls. There was no change
in the percentage of CD5(+)-CD4(+) T cells, MHC class II(+) cells, or ED1(+) macrophages.
However, the percentage of CD5(+)-CD8(+) T cells decreased at 2 days, resulting in
an increased CD4/CD8 ratio, and both parameters returned to control levels after 7
days. Mitogen-induced T and B lymphocyte proliferation increased after 0-28 days post-ischemia
independently of the mitogen used. There was no difference in immune response or norepinephrine
levels between left and right MCA occlusions. These results are consistent with the
notion that cerebral ischemia induces mobilization of certain immune cells from the
periphery to the brain, where they may contribute to the local inflammatory response.
Additionally, the data indicate that cerebral ischemia is followed by a systemic activation
of T and B lymphocytes. Absence of asymmetric effects of left versus right stroke,
and failure to demonstrate any suppressive effects of left-sided lesions on lymphocyte
proliferation, probably reflects the fact that these large cerebral ischemic lesions
affect both cortical and subcortical areas.