Figure 4. Cell trafficking responses induced or increased by mast cells.

Host control and clearance of invading pathogens requires the mobilization of many cell types, both into the site of infection for effective innate immune responses and into draining lymph nodes to initiate appropriate adaptive immune responses. The diverse and divergent cell types that are recruited into infected sites during various models of pathogenesis as a result of mast cell products collectively show the specificity of mast cell-promoted trafficking responses to individual pathogen challenges. a | After entry of a bacterial pathogen, mast cells can become activated and release products that promote many of the necessary cell trafficking events. In models of bacterial pathogenesis, neutrophils are recruited, which are largely responsible for pathogen clearance. Mast cells also enhance the trafficking of dendritic cells (DCs) through infected tissues by mobilizing the DC precursors from the blood and into infected tissues. The activation of several subclasses of DCs has been shown to occur as a result of mast cell activation during bacterial infections, resulting in enhanced trafficking of these cells from infected sites and into draining lymph nodes to initiate adaptive immune responses. Mast cell-derived particles from exocytosed granules can also flow into the lymphatics and travel to draining lymph nodes, where they promote the retention of lymphocytes during the process of lymph node hypertrophy. b | During infection with parasites, eosinophils, basophils and mast cell precursors have been reported to be recruited into sites of infection, such as in the gut. In addition, there is evidence that mast cells proliferate in parasite infection models. c | In viral infection, mast cell activation can promote the chemotaxis of CD8⁺ T cells and natural killer (NK) cells to the peritoneal cavity or in vitro.