Gamma globulins are the plasma proteins and include most of the antibodies. In addition, there are the albumins and - and ß-globulins. The individual groups can be separated from one another by electrophoresis. Patients which cannot form antibodies suffer from a so-called agamma globulinaemia because no globulins are found in the electrophoresis of their serum proteins.

Gene segments: The variable domains of immune receptors are coded in individual gene segments which are assembled into the exon for the complete variable region by somatic recombination. There are three types of such gene segments: the V gene segments code the first 95 amino acids, the D gene segments about five amino acids, and the J gene segments contain the information for the last ten to fifteen amino acids of the variable region. The DNA of the germ cells contains numerous copies of these gene segments, but only one of them is expressed in each case into receptor-bearing lymphocytes.

Gene therapy: In immunology, the correction of a genetic defect by the insertion of a functional gene into bone marrow cells or other types of cells (somatic; generative) is known as gene therapy.

Genetic immunization is a new method for triggering acquired immune responses to a certain protein. Plasmid DNA containing information for the desired protein is injected into muscle tissue. For reasons not yet known, the DNA is expressed in the muscle cells, triggering the formation of antibodies and a T cell response to the protein.

Glycoprotein: Proteins containing carbohydrates, also known as protein sugar.

Graft versus host reaction: A graft versus host reaction occurs when mature T lymphocytes of a donor injected into a recipient who is not genetically identical attack the recipient's cells. Mature T cells from allogen bone marrow transplants can cause the so-called graft versus host disease in humans.

Granulocytes is another word for polymorphonuclear leukocytes.

Granuloma: Site of a chronic inflammation such as that caused by tuberculosis bacteria. The centre of a granuloma consists of phagocytes which have merged.