Latest Immune Models and Hybrid Approaches - Immunological Computation: Theory and Applications - page 159

(Aickelin et al., 2003). h e authors subsequently developed two algorithms—the den-
dritic cell algorithm (DCA) (Greensmith et al., 2006) and the toll-like receptor (TLR)
algorithm (Twycross, 2007). h ese algorithms focus on diff erent aspects of innate
immunity to develop the basis of computation models.

6.1.2 Combining Dendritic Cells and Danger Theory

Yeom (2007) used a similar approach of combining the DT and DCs to form a
schema for the signal precategorization. h is categorization is based on the follow-
ing principles:

PAMPs are proteins expressed exclusively by bacteria, which can be detected
by DCs indicating an anomalous situation.
Danger signals are produced as a result of unplanned necrotic cell death.
On damage to a cell, the chaotic breakdown of internal components forms
danger signals, which accumulate in tissue. DCs are sensitive to changes in
danger signal concentration. h e presence of danger signals may or may not
indicate an anomalous situation; however, the probability of an anomaly is
higher than under normal circumstances.
Safe signals are produced through the process of normal cell death. Cells
must die for regulatory reasons, and the tightly controlled process results
in the release of various signals into the tissue. h ese “safe signals” result in
immune suppression. h e presence of safe signals almost certainly indicates
that no anomalies are present.
Infl ammatory cytokines can be released as a result of injury, although the
process of infl ammation is not enough to stimulate DCs alone, it can amplify
the eff ects of the other three categories of signal.

DCs can stimulate naive T cells and have a number of functional properties
(Yeom, 2007).

DCs' fi rst function is to instruct the immune system to act when the body is
under attack, policing the tissue for potential sources of damage.
DCs perform diff erent functions based on their state of maturation. Modula-
tion between these states is facilitated by the detection of signals within the
tissue, namely, danger signals, PAMPs, apoptotic signals (safe signals), and
infl ammatory cytokines.
In tissue, DCs collect antigen (regardless of the source) and experience danger
signals from necrosing cells and safe signals from apoptotic cells. Maturation
of DCs occurs in response to the receipt of these signals.

According to Yeom (2007), if there is a concentration of danger signals in the
tissue at the time of antigen collection, the DCs become fully mature DCs with