High-density lipoproteins (HDL) inhibit CCL2 production induced by monosodium urate (MSU) crystals in fibroblast-like synoviocytes (FLS). (a, b) FLS were stimulated (grey columns) or not (white columns) for 24 hours with 50 μg/ml MSU crystals in the presence or absence of the indicated concentration of HDL. Alternatively, FLS were pretreated (Ptt.) with the indicated concentration of HDL, washed, and then stimulated for 24 hours with 50 μg/ml MSU crystals. Culture supernatants were analyzed for the production of CCL2 (a) and IL-8 (b). Results are presented as mean ± SD of duplicate determinations and are representative of independent experiments carried out with FLS isolated from three different patients. (c) FLS were stimulated (black columns) or not (white columns) with 10 pg/ml IL-1β for 24 hours. Culture supernatants were analyzed for the production of CCL2. (d) Culture supernatants of FLS, activated as in (a) and (b), were analyzed for their ability to induce mononuclear cell migration, as described in Materials and Methods. Migration induced by culture medium (white column), 10 ng/ml CCL2 (black column), and culture supernatants of FLS activated as in (a) and (b) (grey columns). Four fields were counted for the number of migrated cells. Results represent the mean ± SD of the number of cells/field in four fields. A representative experiment of three is presented.