Immunoglobulin genes

The immunoglobulin-coding genes belong to the so-called assembled genes. Complex genes are created by rearrangements and composition of individual independent gene segments (subgenes). They code for antibodies(immunoglobulins) which, as long as they are located on the B-lymphocyte membrane, are called B-cell receptors.

A distinction is made between the immunoglobulin genes:

• Variable gene segments (V)
• Connecting gene segments (J)
• Constant gene segments (C).
• Diversity segments (D - only in the genloci for the heavy chains).

The different gene segments can be summarized in 3 groups. These are located on different chromosomes.

1. The gene encoding the kappa light chains (κ). This is created by the regrouping of the subgenes Vκ, Jκ and the Cκ gene. A Vκ subgene (out of 40 possible), a Jκ subgene (out of 5 possible) and the Cκ gene are combined to a concrete gene. The resulting rearranged complex gene codes for the entire kappa light chain.
2. The gene that encodes the lambda light chains. This is also a complex gene, which is selected from several subgenes and recombined until a complete DNA for the complete lambda light chain is created.
3. The gene encoding the heavy chain. The coding gene segments are also selected from several subgenes (VH;n=65) D;n=27),JH;n=6) and rearranged until the final DNA for the complete, constant domain of the respective isotype is obtained.

All coding immune complex genes are created in the same way, by rearrangements and recombinations of different subgenes. Each gene coding for the constant domains C_(Cα1-2, Cε,_Cγ1-4, Cdelta) is composed of several exons and introns. The highly variable possibilities of recombining the different subgenes are the basis for the immensely large repertoire of B cells to form specific immunoglobulins. This repertoire is estimated at 10 ¹³ different variants. Thus, for every conceivable allergen a suitable antibody is available.