PRODUCTION OF IL-8 AND MONOCYTE CHEMOTACTIC PEPTIDE-1 BY PERIPHERAL-BLOOD MONOCYTES - DISPARATE RESPONSES TO PHYTOHEMAGGLUTININ AND LIPOPOLYSACCHARIDE

The temporal recruitment of leukocytes to a site of inflammation is de pendent on a complex interplay of a number of soluble mediators. Recen tly, two families of chemotactic cytokines have been discovered. The - C-X-C- family, which includes IL-8, appears to recruit neutrophils and lymphocytes. In contrast, the -C-C- family, which includes monocyte c hemotactic peptide-1 (MCP-1), appears to recruit predominantly monocyt es. Monocytes, after their arrival at a site of inflammation, could fu rther amplify the immune response by secreting IL-8 and MCP-1. We soug ht to define conditions under which human peripheral blood monocytes p roduce IL-8 and MCP-1. Using serum-free media, we found that PHA-stimu lated monocytes expressed MCP-1 and IL-8 protein and mRNA in a dose-de pendent manner. However, the onset of mRNA expression for MCP-1 occurr ed at least 3 h later than did the onset of IL-8 mRNA expression. IL-8 and MCP-1 gene expression by monocytes appeared to require de novo pr otein synthesis, in that cycloheximide blocked the expression of mRNA for both IL-8 and MCP-1 in PHA-stimulated cells. However, treatment of monocytes with cycloheximide resulted in the superinduction of IL-8 c ompared with control monocytes. Monocytes costimulated with PHA and LP S demonstrated enhanced amounts of IL-8 mRNA and protein, but sharply decreased amounts of MCP-1 mRNA and protein. The addition of serum to culture media increased both the constitutive and PHA-induced producti on of monocyte-derived MCP-1 and IL-8, but had no effect on the inhibi tion of PHA-stimulated MCP-1 production by LPS. These findings suggest that distinct pathways of activation exist for the production of mono cyte-derived IL-8 and MCP-1. The differential expression of these diff erent but related polypeptides may offer a means of control of the typ e of immune cells that are recruited to a site of inflammation.