3. TOLERANCE & AUTOIMMUNITY
• Upon encountering an antigen, the immune system
can either develop an immune response or enter a
state of unresponsiveness called tolerance.
• Immunological tolerance is thus the lack of ability to
mount an immune response to epitopes to which an
individual has the potential to respond.
• Targeting type and tolerating type immune
responses composed by the same cellular and
molecular components, the differences are in the
effector phase only.
• Targeting type immune response or tolerance
needs to be carefully regulated since an
inappropriate response –whether it be autoimmune
reaction to self-antigens or tolerance to a potential
pathogen– can have serious and possibly life-
threatening consequences.
6. Passive tolerance
Unresponsiveness: no MHC recognition or
inhibited cellular differentiation.
• Tolerance induced by the nature
of the antigen
• Tolerance induced by the body
7. Passive tolerance induced by the
nature of the antigen
• chemical nature
• dose of the antigen
- low dose tolerance (T cell mediated,
long ranging)
- high dose tolerance (B cell mediated,
short ranging)
• mode of the administration
8. T-cell tolerance
– Central Tolerance (selection in the Thymus)
– Peripheral Tolerance
• Lack of Co-stimulation
• Failure to Encounter Self Antigens
• Receipt of Death Signal
• Control by Regulatory T cells
16. Oral tolerance
Fed antigens can cross the intestinal
epithelial-cell barrier in several ways.
Antigens can be processed and
presented on MHC molecules by
intestinal epithelial cells (a) or cross
through the epithelium, where they are
absorbed into capillaries (b) that drain
into the portal vein and the liver.
Antigens can also be captured by
macrophages (c) and carried to local
draining lymph nodes in lymphatics.
Dendritic cells have recently been
shown to be capable of extending
processes into the gut lumen (d), where
they can capture antigen directly, which
would then allow them to carry antigen
to the local mesenteric lymph node in
lymphatics. Each of these pathways
ultimately converge at the spleen. It
is possible that many redundant
pathways exist to generate tolerance or
that each individual pathway generates
different forms of tolerance to specific
antigens. TCR, T-cell receptor.
17.
18.
19. Tolerance induced by the body
• sequestered antigens
no MHC recognition
no antigen presentation
no systemic response
• heredited or acquired immunodeficiency
• clonal anergies
• tolerance induction
20. ACTIVE TOLERANCE
Anti-idiotype network
• Anti-idiotype antibodies against T cell and B
cell receptors and immunoglobulins
• Antigen-specific inhibition and induction of
memory
• Part of the adaptive immune response
“Immunological homunculus”
• Natural (auto)antibodies: low affinity IgM
autoantibodies produced by CD5+ B cells
• γ/δ T cells
• Innate-like adaptive responses