The genes that are expressed in sick people differ from those who are healthy. Using advanced sequencing techniques, these researchers found that immune cells in the blood of people with Lyme disease express different genes from those of healthy controls. Genes that are linked to a strong immune response were reduced in Lyme patients compared to those with other bacterial or viral infections. People with persisting symptoms attributed to Lyme disease shared some gene expression patterns with patients suffering chronic illnesses caused by immune system dysfunction.