Actions of the chemotactic cytokines MCP‐1, MCP‐2, MCP‐3, RANTES, MIP‐1α and MIP‐1β on human monocytes

Abstract

The activities of six synthetic CC chemokines, MCP‐1, MCP‐2, MCP‐3, RANTES, MIP‐1α and MIP‐1β on human blood monocytes were studied. All CC chemokines elicited a bimodal migration response in vitro. Highest numbers of migrating cells were obtained with the monocyte chemotactic proteins (MCP) and RANTES, somewhat lower numbers with MIP‐1α, and only weak migration with MIP‐1β. The most potent attractants were MCP‐1 and MIP‐1α which reached maximum efficacy at 0.1 to 1 nM. All CC chemokines also induced the release of N‐acetyl‐β‐D‐glucosaminidase from cytochalasin B‐pretreated monocytes. The MCP were most effective (MCP‐1 > MCP‐3 > MCP‐2), RANTES and MIP‐1α showed moderate (1/3 of MCP‐1 activity), and MIP‐1β only minimal activity. Cytosolic free Ca²⁺ changes and exocytosis were used to monitor receptor desensitization. Marked cross‐desensitization was observed among MCP‐1, MCP‐2 and MCP‐3 on the one hand, and RANTES, MIP‐1α and MIP‐1β on the other, indicating receptor sharing within these two subgroups of CC chemokines. The responses to RANTES, MIP‐1α and MIP‐1β were also moderately to markedly desensitized by pretreatment with MCP‐1, MCP‐2 or MCP‐3, while the responses to the MCP were virtually unaffected by pretreatment with RANTES, MIP‐1α and MIP‐1β. These results suggest that the MCP also interact with receptors recognized by RANTES, MIP‐1α and MIP‐1β, but not vice versa. Binding studies were performed with radiolabeled MCP‐1 or MIP‐1α. All MCP competed readily for labeled MCP‐1 yielding a concentration‐dependent sigmoidal displacement curve. Displacement with RANTES, MIP‐1α and MIP‐1β was observed at higher concentrations, but was not complete. Radiolabeled MIP‐1α was displaced efficiently by MIP‐1α or MIP‐1β, but only partially by RANTES. Of the MCP, only MC‐3 completely displaced MIP‐1α, while only partial displacement was observed with MCP‐1 and MCP‐2.