Fig. 8

Mechanism of induction of fibrosis by release of active mediators from mast cells promoting interactions with inflammatory cells and fibroblasts. Mast cell infiltration of the marrow may be primary (neoplastic) or a secondary reactive feature of a variety of conditions. Mast cell activation by cytokines (TNFα), IgE or C5a leads to release of their granule contents (tryptase, histamine, TNFα, chymase). Activation may be blocked by oestrogen and other pharmacological agents. Mast cell products stimulate fibroblasts directly and also indirectly through immune effector cells