Direct Measurement of the Force Generated by a Single Macrophage

Abstract

Department of Bioscience and Biotechnology, Sejong University, Seoul 143-747(Received 1 September 2006)During immune responses, macrophages play important roles in phagocytosis and antigen presen-tation by engulfing pathogenic micro-organisms and cell debris. Since the function of a macrophagehighly depends on a series of physical steps including migration, direct contact and strong bindingto its target, deployment of cytoplasm and membrane, and intake of the target, here we have inves-tigated the mechanical behavior of a macrophage by manipulating it with a flexible pipette that wasused as a force sensor and transducer. We examined the response of a macrophage to mechanicalpulling by a positively charged pipette. We observed that the macrophage initially formed strongbinding to the pipette and migrated along the direction of pulling for some early period. Afterthat period, the macrophage exerted a huge traction force to pull the pipette back and attemptedto retract itself towards its original location. We found that whether it was able to return to theoriginal location depended on the level of applied force. Since the traction force generated by asingle macrophage had not been characterized accurately, we measured the force for the first timeto our knowledge and found the maximum traction force to be around 80 nN. This quantitativemeasurement was made possible by a new and convenient method used to calibrate the stiffness ofthe pipette. Through the study, we acquired a better understanding of the mechanics of and theforce generation by a macrophage.