favorable for their own survival, because the immune system then reacts against harmful antigens and ignores those that are not. Throughout life, the intestinal mucosa continues to be chal lenged by the antigens of the intestinal microbiota and ingested food. As a consequence, an estimated 80% of the immune Clinical Case: A Birthday Surprise Nadia Abramovic is worried about her 5-year-old daughter, Anna. The week started out like any other; as a matter of fact, Anna was still talking about her birthday party the weekend before. But for the past two days, Anna has been pale and stless and complaining that her stomach hurts. When she sees that Anna bloody Mrs. Abramovic immediately calls the pediatrician’s office to make an appointment. Anna’s pediatrician sends a stool sample to the local laboratory for a bacterial culture. How will the laboratory test for the etiology of Anna’s illness? Read on to find out. 708 718 724 731 739