Information Technology Reference
In-Depth Information
mating dynamics that strongly enhanced some mating associations over others (i.e.,
the assortativeness). Hence, mating barriers at the individual level emerged from the
mating dynamics within the population.
Establishing an immune system has some parallels with this view of speciation in
that tolerance and high specificity in immune responses arise in a system with high
degeneracy, i.e. where many cells can interact with each other. The situation is
nevertheless more complex in an immune system because tolerance to self requires
that interactions between 'healthy' self cells should not be productive in terms of
effector functions.
Consider three cells, A, B and C, each with a diverse set of ligands and receptors.
For the purpose of simplicity, assume that each cell can only maintain interactions
with one cell at a time. Consequently, if two cells are conjugated and a third cell starts
an interaction with one of the cells in the conjugate, the conjugated cell has two
alternatives: either it engages in this new interaction or it does not favor the new
interaction and maintains the former one. This decision process implies that cells
perform an integration of the signals they receive and respond after an optimization
process. Cellular frustration arises if a chain of interactions, as shown in Fig.1,
persists such that interactions are never long-lived.
Fig. 1. Cellular frustration among three cells. A system of cells is frustrated if intercellular
interactions do not allow long-lived interactions to emerge. This is schematically presented
here: Initially, cells A and B are conjugated (configuration in the first square). Then C interacts
with cell B, which prevents maintaining the interaction between cells A and B and leads to the
second configuration. If then cell A approaches cell C, the conjugate CB is destroyed and a new
conjugate AC is formed (third configuration). As in other, physical or social, systems, no stable
configuration is reached, and the system fluctuates over several possible states.
Cellular frustration requires several assumptions:
Assumption 1: Cellular Crossreactivity
Cells can interact and potentially react with a large set of other cells.
Assumption 2: Cells are selective
Each cell selects among alternatives and can only maintain interactions with a limited
number of cells. (Here, we use the approximation that one cell can only maintain
long-lasting interactions with one other cell at a given time).
Search WWH ::




Custom Search