Once activated, eosinophils are themselves a source of secreted TNFa which may serve to continue the recruitment of new eosinophils to the site of inflammation. Altered traffic also involves changing how the inflammatory cells migrate through tissue. Most leucocytes migrate into tissue from the circulation. Fundamental to this process is. These adhesion molecules are necessary to keep the inflammatory cell at the target tissue site as well as , in certain cases, participate in the cellular activation process.
Cytokines play a fundamental role in adhesion molecule expression.
The specific biochemical properties of these molecules is a subject for future discussion. Another adhesion molecule of special importance in allergic reactions is VLA-4 . This molecule is expressed on activated lymphocytes, mast cells and eosinophils. It follows that excess, allergen-specific TH2 activity could produce activation of each component of the allergic cascade. It is reasonable to hypothesize that allergic disease is characterized by animbalance between allergen- specific TH1 and TH2 activities.