T- and B-cell-deficient mice with experimental stroke have reduced lesion size and inflammation

Abstract

Stroke induction in immunologically competent mice not only produces local ischemia and brain damage, but also induces early inflammatory changes in brain and peripheral immune responses. Although immune elements clearly are activated after brain vascular occlusion, the relative contribution of T and B lymphocytes to the developing lesion has not been quantified. We evaluated effects 22 h after middle cerebral artery occlusion (90 mins) on histologic injury and peripheral immune activation in severe combined immunodeficient (SCID) mice lacking T and B cells. Cortical and total infarct volumes were strikingly reduced in male SCID mice (n=14, 33+/-4% of contralateral cortex, n=10, 52+/-3% of contralateral hemisphere) versus immunologically intact C57BL/6 mice (wild type, n=9, 57+/-5% of contralateral cortex, 57+/-4% of contralateral hemisphere) (P<0.01). Striatal infarction was not altered (77+/-7% of contralateral striatum in SCID, 84+/-7% in wild type), suggesting that the core of the evolving ischemic lesion was not impacted by lack of T and B cells. As expected, inflammatory factors from immune cells in ischemic SCID brains were essentially absent, with the exception of interleukin-1beta increase in both SCID and wild type tissue. Spleen cell numbers were low in SCID mice, but were further reduced 22 h after stroke, with substantial reduction in most inflammatory factors except for increased expression of interferon-gamma and macrophage inflammatory protein (MIP)-2. These data quantify the damaging effect of T and B lymphocytes on early, evolving ischemic brain injury, and further implicate interleukin-1beta in brain and interferon-gamma and MIP-2 in spleen as inflammatory factors produced by cells other than T and B cells.

Figure 1

Infarction volume (percentage of contralateral structure) is reduced in SCID (n = 14) versus immunologically intact C57BL/6 mice (n = 10, P < 0.01). Data are presented as mean ± SEM.

Figure 2

Effects of MCAO on expression of cytokines and chemokines/receptors in spleen and brain of SCID and C57BL/6 WT mice. Spleen, ipsilateral, and contralateral cerebral hemispheres were collected from three MCAO and two sham-operated mice from each treatment group (WT and SCID) at 22 h of reperfusion. mRNA was prepared from each sample, then analyzed by reverse transcription–PCR in triplicate for relative expression (RE) of cytokines, chemokines and their receptors. RE in each sample is compared with expression of ribosomal reference gene L32. These initial REs for SCID or WT stroke groups were normalized to the relevant companion sham groups. Therefore, data are shown as the fold increase (or decrease) in MCAO tissue relative to matched sham-operated controls: WT (filled bars) and SCID (open bars).