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The cell-to-ce ll interactions during chronic inflammatory diseases likely contribute to leukocyte accumulation leading to increased pathology and organ dys -function. In particular, there is a paucity of information relating to the maintenance of chronic fibrotic diseases . Using a lung fibroblast line and enriched monocyte populations , we have investigated the activational events which contribute to the production of two C-C chemokines , macrophage inflammatory protein-1 alpha (MIP-1α ) and monocyte chemoattractant protein-1 (MCP-1), during fibroblas tmonocyte interactions . Neither the fibroblast cell line (16 lu) nor isolated monocytes alone produced significant levels of MIP-1α or MCP-1. However, when isolated monocytes were layered onto 16 lu fibroblas tmonolayers as ignificant increase in MIP-1α and MCP- 1 production was observed. The use of fixed cell populations indicated that the MIP-1α was derived from monocytes and MCP-1 from both cell populations. To examine the molecules which wer erequired for chemokine production during the interaction, specific antibodies were used in the co-cultures . Blocking β3-integrin interactions s ignificantly inhibited MIP-1α production. In contrast, beta-integr in interactions had no effect on the MCP-1 production, while, neutralization of TNF significantly decreased MCP-1 production during the co-culture . These data indicate that fibroblast–monocyte inte ractions induce chemokine production through different mechanisms and a combination of these responses may contribute to the maintenance of the mononuclear cell accumulation during diseaseprogression.

The role of eosinophils in inflammation and their mode of activation is not well understood. Eosinophil accumulation and subsequent expression of cytokines at the site of inflammation may play a role in exacerbation of inflammatory responses. In the present study, we have examined the role of TNF-α in eosinophil activation and chemokine production using a human leukaemic eosinophil cell line, EOL-1. Initial studies demonstrated that TNF-α induced the upregulation of IL-8 and MCP-1 mRNA and protein. Kinetic studies indicated production of chemokines, IL-8 and MCP-1, as early as 4 h post-activation, with peak levels of chemokine produced at 8 h, and decreasing by 24 h post-TNF-α activation. When IL-10, a suppressive cytokine, was incubated with TNF-α and EOL-1 cells, no effect was observed on IL-8 and MCP-1 production. However, dexamethasone, a glucocorticoid, demonstrated potent inhibitory effects on the EOL-1-derived chemokines. These studies indicate that eosinophils may be a significant source of chemokines capable of participating in, and maintaining, leukocyte recruitment during inflammatory responses, such as asthma.

Monocyte chemotactic protein (MCP-1) is a specific monocyte chemoattractant and activating factor produced by both immune cells (mononuclear phagocytes and lymphocytes) and non-immune cells (parenchymal and stromal cells). In order to define the conditions under which human monocytes express MCP-1, monocytes were exposed to IFN-γ, IL- lβ, TNF-α, IL-4 or PHA under serum free conditions. There was no significant MCP-1 production by monocytes following exposure to IL-lβ, TNF-α or IL-4. In contrast, stimulation with IFN-γ resulted in a dose dependent increase in MCP-1 protein and mRNA expression. Simultaneous stimulation with IFN-γ and IL-1β or TNF-α resulted in no further increase in MCP-1 production. It is concluded that IFN-γ, primarily a product of TH1 T lymphocytes, stimulates the expression of MCP-1 by monocytes.