PWM-activated spleen cell-conditioned medium (SCCM) and a variety of purified hematopoietic growth factors were tested for their ability to stimulate chemotaxis of mouse connective tissue mast cells (CTMC). Of the agents tested, only IL-3 and SCCM promoted mast cell chemotaxis. Neither IL-2, IL-4, GM-CSF, nor endotoxin had any significant mast cell chemotactic activity. Neutralizing antibodies to mouse IL-3 blocked greater than 90% of the chemotactic activity of SCCM, suggesting that IL-3 is the predominant mast cell chemotactic factor produced by activated spleen cells. Our results demonstrate that mature connective tissue type mast cells are capable of moving toward a gradient of spleen cell-derived IL-3 and suggest that movement of mature mast cells toward lymphokines may influence the accumulation of mast cells at sites of inflammatory or immune reactions.

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