The cytokine factor
the inheritance of susceptibility to immunological diseases is governed by what is known as the major histocompatibility complex -- a set of closely-linked system genes. Angelika Daser and colleagues at the Rudolf Virchow University in Berlin highlight the function of another group of genes, which are responsible for making products known as cytokines, which play an important role in promoting or suppressing inflammation, in response to immunological disease ( Cytokine , Vol 8, No 8). Intriguingly, they suggest that a crucial role may be played by regions of cytokine genes, known as control regions, which determine the circumstances under which a gene might act.
In order to appreciate the researchers' thesis, one needs to understand the meaning of the word 'polymorphism'. A gene is said to be polymorphic if there is more than one version of the gene. This situation can result in different individuals in a population having different versions of the same gene. Sheer chance can result in changes taking place in a dna sequence, and if these changes do no harm to the organism, they persist. However, there are known situations in which a changed dna sequence is associated with a diseased state, in which case it is possible that the polymorphism helps in combating the disease.
The critical observation of Daser's team is that cytokine gene polymorphisms are associated with many immunological diseases. The inference is that cytokines and their associated molecules are likely to play a role, not just as passive responders, but as ameliorating agents of the basic genetic conditions that predispose immunological disease. The authors also suggest that perhaps one should use the cytokine polymorphisms as a diagnostic tool to decide whether a disease is immunological or not.
What might be the benefit of having two different cytokine genes? Because the majority of known polymorphisms are in putative control regions, the conjecture is that they serve to allow a certain degree of flexibility in the immune response, something that remains to be tested.