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along the vessel wall and exit the blood stream into the tissue area. Any bac-
terium within the tissue is subsequently attacked by a neutrophil. During
ingestion of a bacterium by a macrophage, tumor necrosis factor (TNF) is
secreted and the bacterium releases lipopolysaccharides (LPS) from its sur-
face. In turn, TNF triggers selectin production in endothelial cells, whereas
LPS induces endothelial cells to produce ICAM.
The following sections explain our model in more detail with respect to clonal
selection as well as primary and secondary responses within a lymph node area
and a tissue region (Section 4.1). The IS processes triggered during a bacterial
infection within the interface area between a blood vessel and tissue is described
in Section 4.2.
4.1
Simulated Viral Infection
Figure 2 gives an overview of the immune system agents and their interaction
patterns in our model. Each agent is represented by a specific, 3-dimensional
shape, which are also used in the (optional) visual representation of the agents
during a simulation experiment. We demonstrate one experiment to show a typ-
ical simulation sequence.
Clonal Selection within a Lymph Node:
In this experiment, we first focus
our attention on a selected lymph node in order to observe the IS agent reactions
after a virus enters the lymph node area (cf. Fig. 1). Initially, 50 B cells as well
as 20 helper-T cells of 8 different types (signatures) are present. Figure 3f shows
that there is a fairly even initial distribution of the different strands of B and T
cells. Around time step
t
=14
.
6, dendritic cells enter the lymph node and present
a single type of viral antigen (Fig. 3b), which stimulates a nearby helper-T cell
and causes a matching B cell (following the Celada-Seiden anity model [12])
to replicate. Soon after (
t
=57
.
1), a significantly larger population of matching
B cells proliferates the lymph node area (Fig. 3c), where B cells have already
started to emit antibodies. In Fig. 3f the concentration of these fast proliferating
B cells is represented by the green plot. At time point
t
= 225
.
0, memory B cells
of the matching strand have become more common. Around
t
= 256
.
4, the same
virus is introduced into the lymph node again. Now it is mainly the memory B
cells that trigger the secondary response and replication of plasma B cells which
secrete antibodies (compare the increase of the matching B cell concentration
(green) towards the last third of the graph in Fig. 3f).
Primary and Secondary Response in Tissue:
At the same time, while the
simulation of the interactions within the lymph node are running, a concurrent,
second simulation models the response processes in a selected tissue area (cf.
Fig. 1). Circulation of IS agents is implemented by a communication channel be-
tween lymph node and tissue areas. Within the tissue simulation space (Fig. 4a),
we start with 10 dendritic cells, 5 killer-T cells, 5 helper-T cells, 5 macrophages,
60 tissue cells and 5 copies of the same virus introduced into the lymph node as
