IMPACT OF T-CELLS ON ASTROCYTES IN VIVO & IN VITRO: IMPLICATIONS POST-ISCHEMIC STROKE

Abstract

Purpose: Post-ischemic stroke, T-lymphocytes enter the brain. The role of T-cells in the progression of cerebral infarction or repair mechanisms is unclear. We hypothesized that T-cells interact with astrocytes directly leading to an anti-inflammatory response. Methods: In vivo, ischemic stroke was induced by middle cerebral artery occlusion in young adult C57/B6 male mice. Mice were sacrificed at 3 days or 1-month post-ischemic stroke. Paraffin-embedded brain sections demonstrated co-localization of astrocytes and CD4+ and CD8+ T-cells in the ischemic region 1 month after stroke. T-cells were harvested from the brain by digestion; percoll enriched, and incubated with anti-CD3 and CD25 antibodies. T-cells were sorted via flow cytometry. The cytokine profile of brain infiltrated CD4+ and CD8+ T-cells were compared to spleen T-cells using QT-PCR. In vitro, C8-S murine astrocyte type II clone cell line (ATCC® CRL-2535™), and T-cells extracted from the spleens of 3-month-old C57/B6 female mice were placed in co-culture at a 1:1 for 48 and 72 hours and compared to individual cell cultures. Anti-CTLA-4 antibodies were added to each culture condition as another experimental group. Astrocytes and T-cells were collected separately for QT-PCR analysis. Results: In vivo, the following cytokine gene expressions poststroke, were found to be elevated: IFNγ, IL-10, IL-17, TNFα, and perforin. In vitro, IL-10 gene expression was elevated in astrocytes and T-cells individually harvested from 1:1 co-cultures compared to astrocytes and T-cells alone at 48 and 72 hours respectively. IL-10 was produced primarily by T-cells stimulated by direct contact with astrocytes. Anti-CTLA-4 antibodies blocked the direct cell-to-cell interaction by reducing IL-10 gene expression in both astrocytes and T-cells. Conclusions: Our data suggests that T-cells release pro- and anti- inflammatory cytokines while in close proximity to astrocytes after ischemic stroke. In co-cultures, astrocytes directly interact with T-cells increasing their IL-10 gene expression by 72 h., implying a neuroprotective mechanism exists via astrocyte stimulation of T-cell IL-10 production.