A technique for studying chemotaxis of leucocytes in well-defined chemotactic fields

The IL sequence in the LLKIL motif in CXCR2 is required for full ligand-induced activation of Erk, Akt, and chemotaxis in HL60 cells

The chemotaxis of differentiated HL60 cells stably expressing CXCR2 was examined in a microfluidic gradient device where the steepness of the CXCL8 chemokine gradient was varied from 2 pg/ml/mum (0-1 ng/ml over a width of 500 microm) to 50 pg/ml/microm (0-25 ng/ml over 500 microm). The differentiated HL60 cells stably expressing CXCR2 exhibited little chemotaxis in response to a 0-1 ng/ml gradient, but displayed an increasing chemotactic response as the gradient steepness increased from 0 to 5, 0 to 10, and 0 to 25 ng/ml, demonstrating that steepness of gradient is a major determinant of the relative ability of cells to persistently migrate up a chemotactic gradient. When HL60 cells expressed CXCR2 mutated in the C terminus LLKIL motif (IL to AA), ligand-induced internalization of receptors was reduced 50%, whereas cell migration along the gradient of CXCL8 was completely lost. Although both mutant and wild-type receptors could mediate Akt and Erk activation in response to CXCL8, the level of activation of these two kinases was much lower in the cell line expressing the mutant receptors. These data imply that the IL amino acid residues in the LLKIL motif are very important for activation of the signal transduction cascade, which is necessary for cells to sense the chemokine gradient and respond with chemotaxis. Moreover, because mutation of the IL residues in the LLKIL motif resulted in only 50% reduction in receptor internalization, and a 50% reduction in Akt and Erk phosphorylation, but a complete loss of chemotactic response, the data imply that IL amino acid residues in the LLKIL motif are key either for amplification or oscillation of crucial signaling events or for establishment of a threshold for signals required for chemotaxis.

Dissipative metabolic patterns respond during neutrophil transmembrane signaling

Self-organization is a common theme in biology. One mechanism of self-organization is the creation of chemical patterns by the diffusion of chemical reactants and their nonlinear interactions. We have recently observed sustained unidirectional traveling chemical redox [NAD(P)H - NAD(P)(+)] waves within living polarized neutrophils. The present study shows that an intracellular metabolic wave responds to formyl peptide receptor agonists, but not antagonists, by splitting into two waves traveling in opposite directions along a cell's long axis. Similar effects were noted with other neutrophil-activating substances. Moreover, when cells were exposed to an N-formyl-methionyl-leucyl-phenylalanine (FMLP) gradient whose source was perpendicular to the cell's long axis, cell metabolism was locally perturbed with reorientation of the pattern in a direction perpendicular to the initial cellular axis. Thus, extracellular activating signals and the signals' spatial cues are translated into distinct intracellular dissipative structures.

Evidence for lymphocyte chemotaxis toward monocytes during PHA-induced aggregation in vitro

An important, early phenomenon during the development of immune cell interactions in vitro is the formation of multicellular aggregates. We have developed a quantitative assay to determine the kinetics of multicellular aggregate formation within a heterotypic population of cells on a flat surface. This assay follows the time rate of change in the value of an aggregation index for cells in undisturbed culture. For an initial, well-separated population of cells, the index is a minimum and remains at this value if the cells do not move and interact. By contrast, for conditions that promote active cell movement followed by interaction, the index value increases with time. The index, which reflects cells' relative spatial distributions, is an "indirect enumeration" of the number of cells within aggregates as a function of time. We used this index to follow the aggregative behavior of a population of freshly isolated human peripheral lymphocytes and monocytes. Previous studies have shown that monocytes are centrally located within aggregates and that lymphocytes move to surround monocytes. In order to test if lymphocyte movements are random or directed prior to interactions with monocytes, we formulated a simple model to describe changes in the expected number of cells in an "idealized aggregate" as a function of time. A comparison of the model curves with curves generated from the changes in the aggregation index shows that the best fit derives from a model that involves directed movement of lymphocytes toward monocytes. These results suggest that monocytes produce a chemoattracting agent for lymphocytes for these experimental conditions.

Neutrophil function and oral disease

The pathological sequela of reduced neutrophil function in the oral cavity and the mechanisms behind dysfunction have added to our understanding of infectious diseases. Numerous examples have been given, and the overriding conclusion must be that any impairment of neutrophil function will lead to some degree of increased susceptibility to infection. Perhaps the tissue most sensitive to pathological changes in the oral cavity is the periodontium. In cases of severe neutrophil dysfunction, there is severe periodontal breakdown, but also in cases of "mild" neutrophil dysfunction, where there is no other infection, such as in individuals with LJP, there is severe periodontal breakdown. The molecular basis of neutrophil dysfunction is beginning to be understood in individuals with LJP, LAD, CGD, and AIDS. It is our hope that further research in this area will help to delineate the pathogenesis of these and other oral diseases.

Neutrophil function and oral disease

The pathologic sequela of reduced neutrophil function have been reviewed. In each case, the mechanism for the reduction in function has been elaborated when known. Special emphasis has been placed upon the pathologic changes in the oral cavity as a result of neutrophil dysfunction. Numerous examples have been given, and the overriding conclusion must be that any impairment of neutrophil function will lead to some degree of increased susceptibility to infection. Perhaps the tissue most sensitive to pathologic changes in the oral cavity is the periodontium. In cases of severe neutrophil dysfunction there is severe periodontal breakdown. But also in cases of "mild" neutrophil dysfunction, where there is no other infection, such as in individuals with LJP, there is severe periodontal breakdown. The molecular basis of neutrophil dysfunction is beginning to be understood in individuals with LJP. It is our hope that further research in this area will help to delineate the pathogenesis of periodontal diseases.

Advantages and limitations of methods for measuring cellular chemotaxis and chemokinesis

Cell migration is an important component of many physiological reactions, for example inflammation, wound healing and formation of atherosclerotic lesions. This review summarizes the methods currently available for examining cell movement in vitro. The applications of each method, and its particular advantages and disadvantages are discussed. Techniques are described for preparing purified leukocyte populations for use in migration studies and for differentiating between chemotactic and chemokinetic cell migration.

A 48-well micro chemotaxis assembly for rapid and accurate measurement of leukocyte migration

We designed a 48-well chemotaxis chamber to minimize manipulation time and amount of material required by the larger blindwell or Boyden chemotaxis chamber. Cell and chemoattractant dose-response curves showed that results were comparable to our better than those obtained with blindwell chambers. The volume of chemoattractant per well is 25 microliter; the number of cells can be as low as 10,000. The time needed for setting up this multiwell unit and for staining the membrane filter sheet is negligible. Combined with the use of an image analyzer to count the number of migrated cells, the method is suitable for clinical research on the functional state of monocytes in large groups of patients.

Rapid quantitation of neutrophil chemotaxis: use of a polyvinylpyrrolidone-free polycarbonate membrane in a multiwell assembly

A neutrophil chemotaxis assay was developd which permits rapid, quantitative assessment of migration across a membrane filter. The critical factor in the assay was the use of a 10 microns thick polycarbonate membrane without the usual polyvinylpyrrolidone coating. Migrated neutrophils remain adherent to the uncoated membrane, whereas 20-50% fall off polyvinylpyrrolidone-coated membranes. A major advantage of the method is that neutrophil chemotaxis can be readily quantified, since the migrated cells adhere to the membrane surface and are in one optical plane for counting. A 25 mm x 80 mm membrane sheet was used in a 48-well micro chemotaxis assembly, which requires only 20,000 neutrophils and 25 microliters of attractant per assay well. Neutrophil chemotaxis was complete within 10-20 min at 37 degrees C, with 20-30% of the cells migrating to N-formyl-methionyl-leucyl-phenylalanine and 40-50% migrating to complement derived C5a.

Pattern prediction for moving cells

A continuous-time Markov chain model consisting of four positional and directional states is used to predict the eventual relative positioning of two motile cell types. It is assumed that the period of observation is small in comparison with the generation time of both cell types. The method is useful in predicting developmental phenomena and is applicable to complex patterns involving more than two types of cells.