Soluble ions more than particulate cobalt-alloy implant debris induce monocyte costimulatory molecule expression and release of proinflammatory cytokines critical to metal-induced lymphocyte reactivity.

Aseptic osteolysis has been associated with excessive immune reactivity to particulate implant debris; however, innate and adaptive immune mechanisms that underlie implant debris reactivity remain incompletely understood. Although particulate debris has been implicated as the major type of implant debris mediating macrophage-induced osteolysis, the degree to which metal ions affect a proinflammatory response (if at all) remains unknown. We hypothesized that both soluble and particulate metal implant debris will induce proinflammatory responses in human monocytes resulting in cytokine production and elevated expression of T cell costimulatory molecules, facilitating adaptive immune responses. We tested this hypothesis by characterizing the response of a human monocyte cell line (THP-1), isolated primary human monocytes and PBMCs challenged with Co-Cr-Mo alloy particles and soluble cobalt, chromium, molybdenum, and nickel ions. Our results indicate that soluble cobalt, nickel, and molybdenum can induce monocyte up-regulation of T cell costimulatory molecules (CD80, CD86, ICAM-1) in human monocytes/macrophages. Furthermore, cobalt, molybdenum ions, and Co-Cr-Mo alloy particles similarly induce elevated secretion of IL-1beta, TNFalpha, and IL-6. Antibody blockade of CD80 and CD86, crucial secondary molecules for adaptive responses, abrogated lymphocyte reactivity to metal challenge in metal reactive subjects. Also the addition of IL-1 receptor antagonist (IL-1ra), (which indirectly blocks pro-IL-1beta and thus IL-1beta release), significantly reduced lymphocyte reactivity in metal-reactive subjects. Thus, both soluble and particulate metal implant debris induce monocyte/macrophage proinflammatory responses that are metal and individual specific. This suggests metal-induced up-regulation of costimulatory molecules and proinflammatory cytokine production is necessary to induce lymphocyte activation/proliferation to metal implant debris. (c) 2009 Wiley Periodicals, Inc.