CD23 is a protein that can be found on allergy-type white blood cells (eosinophils), as well as on the cells that line the gastrointestinal tract. Previous studies have reported increased levels of CD23 in infants with cow's milk allergy. CD23 is also elevated in infants and children with allergic disease, when compared to to children without apparent atopic disease. Moreover, the level of CD23 appears to fall in conjunction with therapy.