Three factors recruit and activate other groups of cells which play a major role in extending the immune response for hours to days. Eosinophils release major basic protein which is damaging to cells. The news to many physicians was that there was more to allergy than immediate reactions mediated by histamine. The idea of a simple, linear type 1 reaction with histamine as the major mediator released has undergone significant evolution as tissue events have been studied in more detail. Even in the simplest tissue-model, the nasal mucosa reacting to a single exposure to pollen antigen, a biphasic response has been described.
Mast cells release three sets of mediators with dramatic, immediate, local and systemic effects.
The big players are histamine, prostaglandins, and cytokines, including leukotrienes B4, C4, D4, E4. All are bronchoconstrictors and increase permeability of blood vessels as in anaphylaxis and asthma. Three chemotactic factors recruit and activate other cells that extend the immune response from hours to days. For reasons which are not well understood, a variety of patterns of cell recruitment occur in chronic inflammatory states - in chronic rhinitis, for example, there may be a predominately neutrophilic or eosinophilic response. These mediators tend to recruit lymphocytic responses which tend to sustain the type 4 or cell-mediated hypersensitivity state in target organs.