Human monocyte chemoattractant protein-1 (MCP-1). Full-length cDNA cloning, expression in mitogen-stimulated blood mononuclear leukocytes, and sequence similarity to mouse competence gene JE

Cellular and molecular aspects of granulomatous inflammation

Recent advances in cellular and molecular biology have provided important new avenues to assess mechanisms of granuloma formation/regulation. For example, current studies have identified various cytokines that can exert a powerful influence on both immune and non-immune cells and dictate inflammatory processes. Some of these cytokines are potentially active during the initiation and maintenance of chronic inflammation, including tumor necrosis factor, interleukin 1, and a novel class of chemotactic cytokines. This latter group of mediators belongs to a super-gene family of immune signals that play a key role in the selective recruitment of inflammatory cells to an area of inflammation. The coordinated synthesis of these cytokines is likely important to the development of the granulomatous response. The participation of molecular signals produced by non-inflammatory cells, fibroblasts, and epithelial cells, also warrants special consideration. These "bystander" cells appear to possess effector cell functions and likely serve an important role in inducing pulmonary granulomatous inflammation. Thus, a clear understanding of the cells and molecular signals involved in the initiation and maintenance of chronic pulmonary inflammation will be necessary to assess lesion development and design more selective/effective therapies.

The human homolog of the JE gene encodes a monocyte secretory protein

The mouse fibroblast gene, JE, was one of the first platelet-derived growth factor-inducible genes to be described as such. The protein encoded by JE (mJE) is the prototype of a large family of secreted, cytokinelike glycoproteins, all of whose members are induced by a mitogenic or activation signal in monocytes macrophages, and T lymphocytes; JE is the only member to have been identified in fibroblasts. We report the identification of a human homolog for murine JE, cloned from human fibroblasts. The protein predicted by the coding sequence of human JE (hJE) is 55 amino acids shorter than mJE, and its sequence is identical to that of a recently purified monocyte chemoattractant. When expressed in COS cells, the human JE cDNA directed the secretion of N-glycosylated proteins of Mr 16,000 to 18,000 as well as proteins of Mr 15,500, 15,000, and 13,000. Antibodies raised against mJE recognized these hJE species, all of which were secreted by human fibroblasts. hJE expression was stimulated in HL60 cells during phorbol myristate acetate-induced monocytoid differentiation. However, resting human monocytes constitutively secreted hJE; treatment with gamma interferon did not enhance hJE expression in monocytes, and treatment with phorbol myristate acetate or lipopolysaccharide inhibited its expression. Thus, human JE encodes yet another member of the large family of JE-related cytokinelike proteins, in this case a novel human monocyte and fibroblast secretory protein.

The acute inflammatory reaction

A major theme in current developments in this field has been the realization that the target tissue, in particular the endothelium, has an active role in initiating and participating in inflammatory reactions and is not a passive target, as was previously thought. Attempts to delineate the mechanisms involved have benefited immeasurably from the application of the modern techniques of molecular and cellular biology, and will continue to do so. It is axiomatic that a fuller understanding of these mechanisms will result in the development of new strategies designed to block the acute inflammatory response more specifically and effectively.

Identification of monocyte chemotactic activity produced by malignant cells

Human malignant cells secrete low molecular size proteins that attract peripheral blood monocytes and may be responsible for the accumulation of tumor-associated macrophages observed in vivo. Similar chemotactic proteins are secreted by cultured vascular smooth muscle cells. The predominant monocyte chemoattractants produced by tumor cells of differing origin were demonstrated to be related to smooth muscle cell-derived chemotactic factor. Thus, a single class of chemotactic proteins is produced by different cell types, which suggests a common mechanism for the recruitment of monocytes and macrophages. These results are significant in view of the potential of macrophages to affect tumor growth.

Monocyte chemotactic protein gene expression by cytokine-treated human fibroblasts and endothelial cells

A number of cytokines are active during the evolution of an inflammatory response, including tumor necrosis factor-alpha, interleukin-1, and novel chemotactic cytokines. This latter group of mediators belong to supergene families of inflammatory signals that play a key role in the selective recruitment of immune cells. In this presentation, we present data demonstrating, for the first time, endothelial cell expression of monocyte chemotactic protein (MCP) mRNA induced by LPS, interleukin-1 or tumor necrosis factor. Human fibroblasts were also found to express monocyte chemotactic factor mRNA in response to interleukin-1 or tumor necrosis factor, but LPS was not effective. In addition, neither primary cultures expressed MCP in response to interleukin-6. These studies demonstrate that non-immune "bystander" cells can play an active role in the recruitment of inflammatory cells via the production of novel chemotactic cytokines.