Fig 4 (cont'd). (A) Influence of monocyte to macrophage maturation on the formation of MGC. Monocytes were cultured with (•) and without (▿) human serum to induce/prevent macrophage maturation and stimulated with conditioned medium. Six different media were compared (Ultradoma-PF, Ultradoma, RPMI 1640, SF3, CG, and RG, the latter two inducing monocyte maturation by themselves). Each point represents the mean of six experiments performed with cells obtained from different donors. Deviations from the mean are caused mainly by the donor variability found on day 0 (fusion rates ranging from 55% to 90%). The capacity to fuse is gradually lost during maturation. Asterisks indicate statistically significant differences between cultures with and without human serum (*P < .05, **P < .01). Two typical examples are shown in the photographs. Following culture in protein-free medium (Ultradoma-PF ) without (B) or in the presence of (C) human serum, formation of MGC is still possible (B) or markedly reduced (C). Stimulation was performed on day 5. Giemsa, original magnification × 50.