In allergic inflammation, a combination of TH2 cell and mast cell activity appear to be most responsible for the initiation of the eosinophilic activities. A major source of chemotactic molecules is the activated mast cell. TNFa is a major proinflammatory cytokine whose activities include chemotaxis. 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 .