Granulocyte and monocyte chemotactic factors: stimuli and producer cells

A role for Cdc42 in macrophage chemotaxis

Three members of the Rho family, Cdc42, Rac, and Rho are known to regulate the organization of actin-based cytoskeletal structures. In Bac1.2F5 macrophages, we have shown that Rho regulates cell contraction, whereas Rac and Cdc42 regulate the formation of lamellipodia and filopodia, respectively. We have now tested the roles of Cdc42, Rac, and Rho in colony stimulating factor-1 (CSF-1)-induced macrophage migration and chemotaxis using the Dunn chemotaxis chamber. Microinjection of constitutively activated RhoA, Rac1, or Cdc42 inhibited cell migration, presumably because the cells were unable to polarize significantly in response to CSF-1. Both Rho and Rac were required for CSF-1-induced migration, since migration speed was reduced to background levels in cells injected with C3 transferase, an inhibitor of Rho, or with the dominant-negative Rac mutant, N17Rac1. In contrast, cells injected with the dominant-negative Cdc42 mutant, N17Cdc42, were able to migrate but did not polarize in the direction of the gradient, and chemotaxis towards CSF-1 was abolished. We conclude that Rho and Rac are required for the process of cell migration, whereas Cdc42 is required for cells to respond to a gradient of CSF-1 but is not essential for cell locomotion.

Cell-associated human retinal pigment epithelium interleukin-8 and monocyte chemotactic protein-1: immunochemical and in-situ hybridization analyses

Human retinal pigment epithelial (RPE) cells secrete chemokines, interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) in response to pro-inflammatory cytokines. In this study we (1) examined the efficiency of human RPE IL-8 and MCP-1 secretion, (2) determined the amount of neutrophil and monocyte chemotactic activity in human RPE cell conditioned media and cell extracts that is attributable to IL-8 and MCP-1, respectively, and (3) assessed the sensitivity of immunohistochemistry and in situ hybridization for detecting chemokine production by cytokine-stimulated human RPE cells. Conditioned media and extracts from human RPE cells stimulated with various physiologic concentrations of interleukin-1 beta (IL-1 beta) (0.2-20 ng ml-1), tumor necrosis factor (TNF-alpha) (0.2-20 ng ml-1) or interferon-gamma (IFN-gamma) (10-1000 U ml-1) were examined to compare secreted and cell associated levels of IL-8 and MCP-1 at various time points up to 24 hr. ELISA demonstrated that IL-8 and MCP-1 are both efficiently secreted by pro-inflammatory cytokine treated human RPE cells. Substantial dose- and time-dependent RPE secretion of IL-8 was observed following stimulation with IL-1 beta or TNF-alpha, but cell associated IL-8 was detectable only after high dose (20 ng ml-1) IL-1 beta stimulation and comprised less than 1% of the total IL-8 induced. Dose- and time-dependent RPE cell MCP-1 secretion was also observed following IL-1 beta > TNF-alpha > IFN-gamma stimulation, with an average of 4% of the total MCP-1 retained within RPE. Bioassays demonstrated neutrophil and monocyte chemotactic activity in conditioned media from stimulated RPE cells, but not in human RPE cell extracts. Inhibition of conditioned media-induced chemotaxis by specific anti-IL-8 or anti-MCP-1 antibodies demonstrated that IL-8 and MCP-1 were responsible for the majority of HRPE-derived neutrophil (> 60%) and monocyte (53-57%) chemotactic activity, respectively. Using in situ hybridization IL-8 mRNA was readily detected within IL-1 beta > TNF-alpha stimulated RPE cells and MCP-1 mRNA easily visualized within IL-1 beta > TNF-alpha > or IFN-gamma stimulated cells. Immunohistochemistry to detect IL-8 was positive only in RPE cells exposed to high dose IL-1 beta (20 ng ml-1) for 8 or 24 hr and was weak. Immunohistochemical staining for MCP-1 in RPE cells was more intense and was visualized within RPE cells stimulated with IL-beta, TNF-alpha, or IFN-gamma. This study demonstrates that: (1) RPE cells efficiently secrete IL-8 and MCP-1 upon stimulation with pro-inflammatory cytokines; (2) secreted IL-8 and MCP-1 account for the majority of human RPE neutrophil and monocyte chemotactic activity; (3) in situ hybridization readily detects IL-8 and MCP-1 mRNA in cytokine stimulated RPE cells; and (4) immunohistochemistry demonstrates cell-associated MCP-1 in cytokine stimulated RPE cells, but only minimal cell-associated IL-8.

Polarised interleukin 8 secretion by HT 29/19A cells

Interleukin 8 is a neutrophil chemotactic and stimulating cytokine induced by various inflammatory stimuli, including tumour necrosis factor, interleukin 1, and endotoxin. The ability of HT 29/19A enterocytes to synthesise interleukin 8 was studied. The results show that interleukin 1 is an important stimulus for interleukin 8 synthesis and secretion by HT 29/19A cells, being more potent than tumour necrosis factor. The tumour necrosis factor and interleukin 1 induced interleukin 8 secretion by HT 29/19A cells was seen to be polarised according to the direction of stimulation. These results support the concept that mucosal cells (enterocytes) may play an important part in initiating mucosal inflammation. Furthermore, it is proposed that HT 29/19A cells constitute a tool to study stimulus directed polarised cytokine secretion.