Biology Reference
In-Depth Information
8
Neurogenic Inflammation
and the “Inflammatory Reflex”:
Two Pathways of Immunoregulation
by the Nervous System
Christian Woiciechowsky
Klinik für Neurochirurgie, Charité-Campus Virchow-Klinikum,
Universitätsmedizin Berlin, Berlin, Germany
8.1 Neurogenic Inflammation: A Spinal Cord Reflex
to Initiate Immune Response
Inflammation
is a process of interactions among soluble factors and different cells
that can arise in any tissue in response to traumatic, infectious, postischemic, toxic,
or autoimmune injury. It leads to an abnormal condition of redness, swelling, heat,
and pain localized to the inflamed tissue. The primary purpose of inflammation is to
eliminate the pathogenic insult and to remove injured tissue components in order to
restore normal architecture or to create a scar.
There are three steps in inflammation:
1.
Initiation
of mechanisms to find and remove foreign and injured material; this is stimulated
by recognition factors of injury. This includes vasodilation and increased capillary perme-
ability due to alterations in the vascular endothelium, which leads to increased blood flow
(
hyperemia
) that causes redness (
erythema
) and entry of fluid into the tissue (
edema
). This
phase of the inflammatory response is neurogenic and is mediated by a spinal reflex. It can
be demonstrated by scratching the skin with a fingernail. The “wheal and flare reaction”
that occurs is composed of (a) initial blanching of the skin due to vasoconstriction; (b) the
subsequent rapid appearance of a thin red line when the capillaries dilate; (c) a flush in the
immediate area, generally within a minute, as the arterioles dilate; and (d) a wheal, or swol-
len area, that appears within a few minutes as fluid leaks from the capillaries. It is usually
terminated after several tens of minutes.
2.
Amplification
of response through activation of soluble and cellular inflammatory media-
tors. This includes the acute cellular response that takes place over the next few hours. The
hallmark of this phase is the appearance of neutrophils in the tissues. These cells attach
themselves to endothelial cells within the blood vessels (
margination
) and cross into the
surrounding tissue (
diapedesis
). If a vessel is damaged, fibrinogen and fibronectin are
