Today, allergic contact eczema is diagnosed by a patch test, where a number of allergens are placed on the skin. The test shows the substances to which the person is allergic. The patch test is widely used, but it is time-consuming for both the patient and physician. Research is on-going into a new method, using gene technology, to diagnose allergic contact eczema with a single blood test.
Genes are both active and passive.
Humans have 23 pairs of chromosomes, which, with few exceptions, are found in all the cells of the body. These chromosomes contain all our genes. All the cells in our bodies therefore contain the same genes, but the genes have no effect unless they are ‘expressed’. ‘Expressed’ means that a protein is created from a code that lies within the gene. Each gene is ‘coded’ for a specific protein, and it is this protein that carries out the gene’s function. Different cell types express different sets of genes. In this way, all cell types have their unique make-up and function. A white blood cell, for example, will not express the same genes as a nerve cell.
Active genes can be measured
There are different techniques to measure which genes are expressed in a cell. Measuring gives an insight into the cell’s general function, and it can also give an idea of the state of the cell at the precise moment of measurement. For example, it will show whether a white blood cell is actively involved in an immune response or whether it is in a passive state. One of the most effective ways of measuring gene expression is DNA microarray technology. With this technology, the total gene expression in a cell can be studied by measuring the expression of all the cell’s genes simultaneously.
White blood cells are crucial
White blood cells play a central role in allergic contact eczema. When the white blood cells encounter the substance to which the person is allergic, they are activated to release a large number of genes. The genes expressed by the white blood cells during the disease process can be examined by isolating the white blood cells from a blood sample and stimulating them with the relevant allergen. For example, if the white blood cells from a person who is allergic to nickel are stimulated with nickel, a number of genes will alter their gene expression. In contrast, there will be little alteration in gene expression if the white blood cells are isolated from a person who has no allergy.
It will, however, be several years before we know if a diagnostic test based on a blood sample will be a reality for allergic contact eczema.
This article was published in the journal Astma-Allergi in 2006.
