Leukocyte locomotion and chemotaxis are critical processes in inflammation, where polymorphonuclear leukocytes (PMNs) migrate to sites of infection or injury. The study by Zigmond and Hirsch explores the mechanisms behind this migration and identifies a cell-derived chemotactic factor. They developed a direct morphological method to distinguish between locomotion and chemotaxis, using a slide and cover slip system to observe PMN behavior in response to chemotactic substances like AgGG. This method revealed that PMNs can release substances that stimulate locomotion and chemotaxis, even in the absence of serum. The study also used the Millipore chamber assay to evaluate locomotion and chemotaxis, finding that the distance cells move into the filter is a more reliable indicator of chemotaxis than the number of cells on the filter's bottom. The results showed that PMNs respond to chemotactic stimuli by moving toward the source, with the extent of movement depending on the concentration of the stimulus. The study also demonstrated that cell-derived factors, such as those released from PMNs, can stimulate locomotion and chemotaxis, with the activity being heat-stable and not easily dialyzable. The findings suggest that PMNs are the primary source of chemotactic factors, and that these factors are produced through processes like glycolysis. The study highlights the importance of distinguishing between locomotion and chemotaxis in understanding the mechanisms of leukocyte migration.Leukocyte locomotion and chemotaxis are critical processes in inflammation, where polymorphonuclear leukocytes (PMNs) migrate to sites of infection or injury. The study by Zigmond and Hirsch explores the mechanisms behind this migration and identifies a cell-derived chemotactic factor. They developed a direct morphological method to distinguish between locomotion and chemotaxis, using a slide and cover slip system to observe PMN behavior in response to chemotactic substances like AgGG. This method revealed that PMNs can release substances that stimulate locomotion and chemotaxis, even in the absence of serum. The study also used the Millipore chamber assay to evaluate locomotion and chemotaxis, finding that the distance cells move into the filter is a more reliable indicator of chemotaxis than the number of cells on the filter's bottom. The results showed that PMNs respond to chemotactic stimuli by moving toward the source, with the extent of movement depending on the concentration of the stimulus. The study also demonstrated that cell-derived factors, such as those released from PMNs, can stimulate locomotion and chemotaxis, with the activity being heat-stable and not easily dialyzable. The findings suggest that PMNs are the primary source of chemotactic factors, and that these factors are produced through processes like glycolysis. The study highlights the importance of distinguishing between locomotion and chemotaxis in understanding the mechanisms of leukocyte migration.