Biomedical Engineering Reference
In-Depth Information
Classic pathway
(activated by protamine)
Alternative pathway
(activated by contact
with foreign surface or
microbes)
Antigen-antibody-C1q
C4
C4b.C2b
C5
C2
C3
C4b.C2b.C3b
C3b
C3
C3a
C5b
C5a
Lectin pathway
C5b.C6-9
(MAC)
1.2
The three pathways of the complement cascade. Activation of the
complement system of proteins is an early event in contact activation
and the infl ammatory process. Contact between complement
components and artifi cial surfaces or microbes activates the
alternative pathway. Activation of the classic pathway follows antigen-
antibody reactions and occurs during cardiac surgery, probably as a
result of administration of protamine. The complex C5-C9 or
membrane attacking complex (MAC) is a highly cytotoxic agent that
constitutes the fi nal product of the reaction.
following coronary artery stenting. MBL and sC5b-9 levels have been
shown to be independently associated with cardiac dysfunction after coro-
nary artery stenting (Haahr-Pedersen
et al.
, 2009).
Adaptive immunity
follows innate immunity and mounts a response
adapted to specifi c antigens. Its components include T and B lymphocytes,
antibodies and cytokines. It is further subdivided into humoral and cellular
immunity (Fig. 1.3). Humoral immunity involves antibodies, produced by B
lymphocytes that bind extracellular antigens for disposal via various mecha-
nisms such as phagocytosis and activation of complement. Cellular immu-
nity involves T lymphocytes that can particularly target intracellular micro-
organisms that are inaccessible to antibodies. There are two classes of T
lymphocytes, which include helper T cells and cytotoxic T cells, character-
ised by expression of CD4 and CD8 surface markers respectively. While
cytotoxic T cells directly kill foreign antigens, helper T cells are able to assist
in the disposal of foreign antigens by activation of B cells, phagocytic cells,
NK cells and cytotoxic T cells through the release of cytokines. T lympho-
Search WWH ::
Custom Search