Biology Reference
In-Depth Information
7
Antigenic Recognition
by the Brain: The Brain
as an Immunocompetent Organ
Istvan Berczi
Department of Immunology, Faculty of Medicine, The University
of Manitoba, Winnipeg, Manitoba, Canada
7.1 Introduction
Paul Ehrlich postulated more than a century ago that the cells mediating immune
function express specific receptors (side chains) for antigen (AG), and that upon AG
stimulation the receptors are shed and become antibodies
[1]
. Today the existence of
antigen-specific receptors on B and T lymphocytes and on cells of innate immunity
has been proven. The prevailing view is that the immune system is capable of antigen
recognition, that it develops an immune response followed by memory, and that it is
an autonomous system which provides defense for the host organism
[2]
. However,
recent developments in neuroimmune biology show that the immune system (IS) is
part of the neuroimmune supersystem (NISS), which also involves the central ner-
vous system (CNS) and the endocrine system (ES)
[3]
.
Some 25 years ago, Blalock hypothesized that the immune system is capable of
chemical sensation
[4]
. At that time there was no concrete evidence for his proposal.
Now we understand a lot about the signaling of the CNS by various immunologi-
cal events. In this chapter, we briefly discuss how the brain recognizes foreign and
altered chemical structures that may occur in the host organism (e.g., infections,
trauma, degenerative conditions, cancer) and how it mobilizes the proper mecha-
nisms in the cause of host defense.
7.2 The CNS Has Innate Immune Receptors to Sense
Antigens Directly
7.2.1 TLR Expression in the Brain
The brain, neurons, and axons express toll-like receptors (TLRs) known as TLR8
[5]
.
In the human and mouse brain, mRNA for all TLRs is present, yet it is TLR2 and
4 that are most highly expressed. On microglia, TLR expression is widespread, as
