COMPARISON OF BIOLOGICAL RESPONSES OF HUMAN MONOCYTES AND THP-1 CELLSTO CHEMOKINES OF THE INTERCRINE-BETA FAMILY

The biological responses of human monocytes and cells of the monomyelo cytic THP-1 cell line to stimulation with members of the beta chemokin e family are described in this report. All three chemokines tested, MC P-1, MIP-1 alpha, and RANTES, elicited mobilization of intracellular f ree calcium in monocytes and THP-1 cells. The magnitude of response wa s highest with MCP-1 stimulation. MCP-1 desensitized monocyte response s to MIP-1 alpha and RANTES, but no such desensitization was observed in THP-1 cells. hlIP-la or RANTES did not desensitize either monocytes or THP-1 cells to MCP-1 stimulation. All three chemokines elicited a potent chemotactic response in monocytes that was comparable in magnit ude to that of f-Met-Leu-Phe. MIP-1 alpha and RANTES required a fivefo ld higher dose than MCP-1 to elicit a peak response. On the contrary, THP-1 cells showed no significant chemotactic response. Studies of the desensitization of the monocyte chemotactic response indicated that a ll three chemokines are capable of causing complete homologous desensi tization. Heterologous desensitization was observed only when monocyte s were treated with MCP-1 followed by MIP-1 alpha or RANTES. Studies o f actin polymerization and cell polarization responses of monocytes in dicated that these two responses attained peak magnitude after 10 min of stimulation with any of the chemokines. Dose-response kinetics were similar to those of the chemotactic response. THP-1 cells again faile d to show either of these two responses. Finally the activation potent ial of the chemokines was measured by their ability to induce respirat ory burst. A tenfold higher concentration than that causing peak chemo tactic response was required to elicit respiratory burst and no hetero logous desensitization was noticed. Respiratory burst could be induced in THP-1, cells with a direct protein kinase C activator but not with any of the chemokines. These results indicate that, of the three exam ples tested, MCP-1 is the most potent member of the beta chemokine fam ily in the biological responses examined. Although a calcium response was elicited in THP-1 cells with chemokines, a lack of subsequent resp onses indicates some missing links in the downstream signal transducti on pathways.