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at and near the lesion epicenter. Myelin sparing was improved for a distance
of 900
m
m rostral and caudal to the lesion epicenter, and motor neuron sur-
vival was increased over more than 600
m
m rostral and caudal to the lesion
epicenter. Serotonergic sprouting 1 mm caudal to the injury was also
increased more than 60% in rSLPI-treated animals (
p
<
0.05) as compared
to injured control mice.
To identify how systemic delivery of rSLPI could have such beneficial
effects in the spinal cord, we examined the localization of SLPI
in vivo
before and after injury. Because SLPI had previously been reported to
localize to leukocyte nuclei where it could bind to NF-
k
B binding sites
to attenuate the expression of proinflammatory immune response genes
(
Taggartetal.,2005
), we focused on leukocytes in the peripheral circula-
tion. We found that after a single intraperitoneal injection of rSLPI in adult
mice with SCI, almost 100% of the leukocytes in the peripheral circulation
were immunoreactive for SLPI at 3 h after injection as compared to only
30% of cells from vehicle-treated mice. Importantly, based on optical den-
sity measurements, we found a fourfold greater SLPI immunoreactivity in
rSLPI-treated mice as compared to vehicle-treated controls. This data
clearly indicate that rSLPI is likely to be taken up by leukocytes in the cir-
culation. Western blot of the injured spinal cord also showed increased
SLPI and I
k
-B
a
, the inhibitor of NF-
k
B activity, in rSLPI-treated mice
at 12 and 24 h, relative to vehicle-treated controls. Increased SLPI immu-
noreactivity was found in small, round cells in the injury site that appeared
to be infiltrating leukocytes. mRNA analysis of cytokines regulated by
SLPI and NF-
k
B showed a 40% reduction in TNF-
a
levels (
p
<
0.05)
12 h after SCI.
Our data suggest that SLPI can modulate the inflammatory milieu of the
injured spinal cord, resulting in beneficial effects on locomotor recovery and
tissue protection during the first week after injury, by exerting anti-
inflammatory effects. These inflammatory effects are likely due to NF-
k
B-mediated production of TNF-
a
and other proinflammatory molecules.
While only one or two injections of rSLPI were effective in other models
of peripheral inflammation such as arthritis (
Song et al., 1999
) and skin
wound (
Ashcroft et al., 2000
), daily treatment was required for improved
recovery after SCI. The reasons for this are not known at present. Our data
provides further evidence that during the first week after injury, the spinal
cord tissue environment is one that promotes secondary tissue damage,
which can be reduced at least in part by treatment with rSLPI as endoge-
nously produced SLPI is not sufficient to provide effective protection.
