Affinity maturation

The affinity maturation (english affinity maturation ) is a process of the immune system of mammals, whose mission is to improve the efficiency of the immune response after repeated exposure to an antigen. The affinity maturation occurs in mature B lymphocytes in the germinal centers of lymph nodes and is based on a, also known as somatic hypermutation increased mutation rate in these cells and a clonal selection. It is long instead of the V (D) J recombination, that is responsible for the inherent diversity of the B-lymphocytes. The natural process of affinity maturation is mimicked under artificial conditions to improve recombinant antibodies and antibody fragments, and thus referred to as in vitro affinity maturation.

Physiology

After first time matching IgM -bearing B lymphocytes with an antigen presented, the majority of these cells to plasma cells, which are responsible for the production of antibodies of the IgG type differentiated. Another part travels in the germinal centers of the lymph nodes, where random, the variable domains of the light and heavy chains of immunoglobulins carried respective mutations. The mutation rate is up to 1,000,000 increased in comparison to other somatic cells, resulting in an average time of a mutation within the variable domains per cell generation. Plays an important role in this form of somatic hypermutation the Activation Induced Cytidine Deaminase ( AID) a. For the survival of the so- mutated B- lymphocytes, it is essential that they enter into an interaction with the presented antigen of follicular dendritic cells via their membrane-bound antibodies. Here, they compete not only among themselves but also with the IgG antibodies formed as a result of the primary response of plasma cells. Through the competition 's survival of the B- lymphocytes, which presented antibodies having improved affinity for antigen. From a large number of educated mutants ultimately survive only very few clones. After this selection, the surviving B- lymphocytes differentiate into memory cells while maintaining the genetic information of the mutated and selected antibodies. Renewed contact with the antigen concerned, these can be activated immediately to ask in a short time these optimized antibodies are available.

Biotechnological use

Following the model of in vivo affinity maturation in vitro affinity maturation is used in biotechnology for the increase in affinity of antibodies and antibody fragments under laboratory conditions. She uses as her idol mutation and selection to improve the efficiency. The in vitro affinity maturation is particularly applicable to antibodies and fragments derived therefrom application that were not subject to affinity maturation in vivo. These include in particular those which have been found by screening of synthetic or naive antibody libraries. In addition, the principle of in - vitro affinity maturation can also be applied to other biomolecules, such as antibody mimics extended.

For the in vitro affinity maturation display techniques such as used phage display. They offer the advantage that a protein is expressed on the surface indirectly linked to the encoding DNA. The encoding DNA may be varied with the aid of chain shuffling, or using mutagenesis techniques, such as using mutator strains of E. coli, β - radiation, chemical mutagens, or error-prone PCR. Using display techniques for the selection of antibody fragments with an affinity in the low nanomolar range can be reached in two to three cycles of mutation and selection.