Tissue responses to implanted materials - Biomaterials and Devices for the Circulatory System - page 9

B-Lymphocytes

Extracellular
antigen

Antibody

+ Plasma

cell

Complement

Activation of
phagocytes and B
lymphocytes

+ Cytokines

CD4+ T lymphocyte Phagocyte

+

CD8+ T lymphocyte Infected cell Killing

1.3 Lymphocyte classes participating in adaptive immunity.

cytes recognise foreign antigens only once they are broken down into
smaller fragments and presented by antigen presenting cells in association
with major histocompatibility complexes (MHC). There are two classes of
MHC molecules, also known as human leucocyte antigen (HLA). MHC
Class I molecules present intracellular antigen fragments to cytotoxic T cells
and MHC Class II molecules present extracellular antigen fragments to
helper T cells, with subsequent processing of antigens as described above
(Kindt et al. , 2007).
Recipients of implantable ventricular assist devices (VAD) are prone to
local and systemic infections and infl ammatory response. These have been
attributed to the immunologic consequences of the devices resulting in
defects in cellular immunity and aberrant T-cell activation. It has been
shown that T cells undergo accelerated programmed death, known as apop-
tosis, within the fi rst few weeks after VAD implantation. The immunological
reaction to VADs is probably biphasic and involves an immediate rise in
soluble death-inducing receptors (Ankersmit et al. , 2002). The neo-intima
covering the textured surface of some VADs contains activated T cells and
monocytes. These changes signify the cellular response to the artifi cial
surface. Furthermore, signifi cant increases in anti-HLA antibodies (allosen-
sitisation) are observed 1 and 3 months after implantation of the HeartMate
I (Thoratec Corporation, Pleasanton, Ca) VAD (George et al. , 2008). The

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