Quorum sensing

Central tolerance and Peripheral tolerance

Having survived negative selection against M self-peptides, the chance of activation against a random peptide is small

For EP=EN=Ea the extreme value properties yield  p=1/M

We shall use the estimates: M~7,000  and   p~10 -5

A large repertiore to T cells is thus needed to detect a pathogen peptide

Estimates of number of  distinct T cells give  T >5x106

Since thymic selection is stochastic, a given TCR cannot be exposed to the entire self-peptide reperoire,

  estimated to have size P~104; resulting in a self-activation probability of

Given the large number of T cells, the chance of non-self-reactivity is small!

T.C. Butler, MK, & A.K. Chakraborty, PNAS 110, 11835 (2013)

propose that immune response requires collective decision of   t    T cells:

                          

Distinguishing between self and pathogen peptides requires

The predicted number of T cells for such quorom is

Preliminary evidence of this in experiments injecting mice with controlled number of T cells.