Monocyte chemotaxis is severely depressed in patients with advanced
tumors, but the cellular basis for this chemotactic defect is not known. Because the
actomyosin cytoskeleton is thought to play a primary role in chemotaxis, we have employed flow cytometry to examine several aspects of the contractile machinery including
myosin II,
myosin light chain kinase (MLCK), actin, and cytoplasmic
calcium in unstimulated and in formylpeptide-stimulated neutrophils and monocytes. Serum-pretreated polymorphonuclear leukocytes (PMNs) and monocytes from healthy blood donors or PMNs and monocytes isolated from
tumor patients were studied. Leukocytes pretreated with serum from
cancer patients exhibited decreased baseline
myosin staining and a vastly different response to formylpeptide stimulation compared with leukocytes pretreated with normal human serum. In contrast, similar amounts of MLCK were observed in neutrophils and monocytes preincubated with normal or
cancer serum with or without stimulation with formylpeptide. The fluorescent
calcium indicator fluo-3 showed that resting and fMLP-stimulated levels of intracellular
calcium were not significantly different in control and
cancer serum-pretreated human leukocytes or in leukocytes isolated from
tumor patients. Similarly, resting and fMLP-stimulated levels of
F-actin in
cancer patients' leukocytes as assessed by NBD-
phallacidin staining did not differ significantly from those of normal leukocytes. Because the
actomyosin cytoskeleton is intricately involved in leukocyte chemotaxis, alterations in the cytoskeleton may dramatically affect cell motility. The cytoskeletal alterations and changes in the response of leukocytes pretreated with
cancer patients' serum to formylpeptide stimulation as described here may result in decreased chemotaxis by these cells.