Lack of interleukin-6 expression is not protective against focal central nervous system ischemia.
OBJECTIVE
Interleukin-6 (IL-6) appears to be involved in the inflammatory response associated with central nervous system (CNS) ischemia. Although IL-6 levels increase after stroke, it is not known whether IL-6 directly influences CNS ischemic injury. In this study, we used a focal reversible stroke model to investigate whether mice lacking IL-6 were protected against acute ischemic injury.


METHODS
We bred IL-6-deficient C57 black mice (I-129 IL-6 KO back-crossed with C57), including homozygous knockouts (IL-6 -/-), heterozygous littermates (IL-6 +/-), and normal littermates (IL-6 +/+). The status of all animals was confirmed by DNA sampling and polymerase chain reaction analysis. Reversible middle cerebral artery occlusion was produced by advancing a silicone-coated 8-0 filament into the internal carotid artery for 2 hours (experiment 1) or 45 minutes (experiment 2). At 24 hours, animals were evaluated on a 28-point clinical scale, blood and cerebrospinal fluid were obtained, and the brains were evaluated for infarct volume and IL-6 mRNA levels.


RESULTS
In experiment 1 (severe ischemia), no differences were seen in lesion size or neurological function between the groups: lesion volume was IL-6 -/- (n=15), 57+/-13 mm(3); IL-6 +/- (n=15), 58+/-23 mm(3); and IL-6 +/+ (n=15), 58+/-18 mm(3) (P=NS). ELISA testing confirmed very low to absent levels of IL-6 in the serum and cerebrospinal fluid of knockout animals. Brain mRNA levels of the other proinflammatory cytokines, including tumor necrosis factor-alpha, IL-1beta, and IL-1 receptor antagonist, were 50% lower in IL-6-deficient ischemic animals than in normal animals. In experiment 2 (mild ischemia), no differences were seen in lesion size or neurological function between the groups: lesion volume was IL-6 -/- (n=10), 16+/-8 mm(3); IL-6 +/- (n=10), 14+/-4 mm(3); and IL-6 +/+ (n=10), 19+/-12 mm(3) (P=NS).


CONCLUSIONS
In this study, infarct size and neurological function at 24 hours were not different in animals deficient in IL-6 after transient CNS ischemia. This suggests that IL-6 does not have a direct influence on acute ischemic injury. Further study investigating the role of IL-6 on long-term recovery after stroke is in progress.
Clark
W M
WM
Oregon Stroke Center, Departments of Neurology, Oregon Health Sciences University, Portland, OR 97201, USA. clarkw2ohsu.edu
Rinker
L G
LG
Lessov
N S
NS
Hazel
K
K
Hill
J K
JK
Stenzel-Poore
M
M
Eckenstein
F
F
D000208:Acute Disease; D000818:Animals; D001921:Brain / Q000098:blood supply* / Q000276:immunology / Q000503:physiopathology; D002544:Cerebral Infarction / Q000235:genetics / Q000276:immunology / Q000503:physiopathology; D005260:Female; D015870:Gene Expression / Q000276:immunology; D015850:Interleukin-6 / Q000235:genetics*; D002546:Ischemic Attack, Transient / Q000235:genetics / Q000276:immunology* / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020127:Recovery of Function; D020521:Stroke / Q000235:genetics / Q000276:immunology* / Q000503:physiopathology; D013997:Time Factors
D015850:Interleukin-6