Mechanisms involved in eosinophil migration. Platelet-activating factor-induced chemotaxis and interleukin-5-induced chemokinesis are mediated by different signals.

Eosinophils play an important role in the pathogenesis of allergic diseases such as allergic asthma. Eosinophil migration in vitro can be divided into directed migration, or chemotaxis, and random migration, or chemokinesis. Here, we studied intracellular signals involved in eosinophil migration in vitro induced by platelet-activating factor (PAF) and interleukin-5 (IL-5), applying a Boyden chamber assay. Migration induced by PAF (10(-11)-10(-6) M) largely consisted of chemotaxis with some chemokinesis, whereas IL-5 (10(-12)-10(-8) M) induced chemokinesis only. Eosinophils were depleted from intracellular and extracellular Ca2+ to study the role of Ca2+ as a second messenger. Ca2+ depletion did not change PAF-induced chemotaxis, however, IL-5-induced chemokinesis was inhibited. Interestingly, PAF, but not IL-5, induced changes in [Ca2+]i. This rise originated mainly from internal stores. Inhibition of protein kinase A by H-89 and protein kinase C by GF 109203X had no effect on both forms of eosinophil migration. Addition of the protein kinase inhibitor staurosporine significantly inhibited IL-5-induced chemokinesis. Inhibition of tyrosine kinases by herbimycin A completely blocked IL-5-induced chemokinesis. PAF and IL-5-induced actin polymerization was studied to compare migratory responses with a migration-associated intracellular response. Ca2+ depletion significantly enhanced PAF-induced (10(-8) M) actin polymerization, whereas IL-5-induced actin polymerization was not influenced. Addition of staurosporine led to an increase in F-actin. Subsequent addition of PAF or IL-5 resulted in an additive increase in F-actin content. In summary, both forms of eosinophil migration are protein kinase A and protein kinase C independent. In contrast to PAF-induced chemotaxis, Il-5-induced chemokinesis was found to be completely Ca2+ and tyrosine kinase dependent.

RANTES- and interleukin-8-induced responses in normal human eosinophils: effects of priming with interleukin-5.

We report that responses of normal human eosinophils toward the chemokines RANTES and interleukin-8 (IL-8) are modulated and upregulated by priming with IL-5. In a modified Boyden chamber assay, we studied migratory responses toward the members of the chemokine family RANTES, monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1 alpha (MIP-1 alpha) (C-C subfamily), and IL-8, platelet factor-4 (PF-4), and neutrophil-activating peptide-2 (NAP-2) (C-x-C subfamily). These chemokines were also studied in terms of actin polymerization and ([Ca2+]i)-mobilizing properties, intracellular signals that are thought to play a role during migratory responses. We found that eosinophils showed significant migratory responses toward RANTES and IL-8 at concentrations of 10(-9) to 10(-7) mol/L only after priming with IL-5 (10 pmol/L). At these concentrations, PF-4, NAP-2, MCP-1, and MIP-1 alpha induced no significant migratory responses after priming. Unprimed eosinophils only showed a significant migratory response toward RANTES (10(-6) mol/L). Changes in [Ca2+]i were found after addition of RANTES, MIP-1 alpha, and NAP-2 (10 nmol/L) to unprimed eosinophils. RANTES (10(-9) to 10(-7) mol/L) significantly induced actin polymerization both in primed and unprimed eosinophils, whereas IL-8 (10(-9) to 10(-8) mol/L) and MIP-1 alpha (10(-8) mol/L) only induced actin polymerization after priming with IL-5. NAP-2, PF-4, and MCP-1 did not affect actin polymerization. These findings are further evidence for the hypothesis that cytokines like IL-5 and locally secreted chemokines like RANTES and IL-8 are both at the basis of specific eosinophil influx into the allergic inflammatory locus.

Pulmonary surfactant protein A enhances the host-defense mechanism of rat alveolar macrophages.

The effects of surfactant, surfactant lipids, and surfactant protein A (SP-A) on the surface phagocytosis of [3H]thymidine-labeled Staphylococcus aureus (SAE) by rat alveolar macrophages were studied. Alveolar macrophages only ingest SAE when the bacteria are opsonized with rat serum prior to incubation with alveolar macrophages. Preincubation or "opsonization" of the bacteria with surfactant did not result in phagocytosis by the macrophages. However, preincubation of the macrophages with surfactant increased the phagocytosis of rat serum-opsonized bacteria by approximately 70% when compared to the control macrophages. The factor present in surfactant causing the stimulation of the phagocytosis is probably SP-A. Preincubation of macrophages with human SP-A enhanced the phagocytosis to the same extent as whole surfactant, whereas preincubation with surfactant lipids had no effect on the phagocytosis. The SP-A-induced enhancement of the phagocytosis is time, temperature, and concentration dependent. Phagocytosis of opsonized SAE by alveolar macrophages was maximal after 15 min of incubation and at an SP-A concentration of 1 micrograms/ml. No phagocytosis occurred at 0 degrees C. In addition, whole surfactant and SP-A induce a lucigenin-dependent chemiluminescence response in alveolar macrophages. The chemiluminescence response is initiated after 15 min of incubation and reaches a maximum after 30 min. The concentration of SP-A needed for an optimal response is in the same order of magnitude as the concentration needed for maximal enhancement of the phagocytosis of SAE by alveolar macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)