Adaptive Immune System

The adaptive immune system has evolved to the body from the everchanging landscape pathgens.

Two arms of the adaptive immune defense:

B cells (antibodies target pathogens)  &  T cells (target infected cells)  [slides from A.K.Chakraborty]

T cells recognize (self) cells harboring pathogen:

Antigen presenting cells (APCs) internally process self and foreign proteins, cut them to short peptides (8-15 amino acids).

The peptides are presented on APC surface, attached to protein MHC.

T cell receptors (TCRs) recognize pathogen peptides by binding to them strongly.

T cell receoptors (TCRs) & B cell receoptors must be

Diverse: to recognize an evolving landscape of pathogens

The combinatorics of V(D)J recombination (video1, video2)

can probably generate more than 1013 distinct combinations.  [See Dudko/Murre]

Self-tolerant: to avoid auto-immune diseases

Specific: to lock on specific pathogens

for immunological memory (vaccination)