Cell-specific activation of p38MAPKα, ERK and JNK in the inflamed synovial membrane. Microphotographs showing synovial tissue of human tumour necrosis factor transgenic (hTNFtg) mice stained for the phosphorylated forms of p38 mitogen-activated protein kinase (MAPK)α (upper panels) and extracellular signal-regulated kinase (ERK; middle panels), and cell-specific markers for (a,b) macrophages, (c,d) fibroblasts, (e,f) T lymphocytes and (g,h) B lymphocytes. p38MAPKα is most frequently present in macrophages (panel a; simultaneous brown and blue staining, black arrows) and less frequently in fibroblasts (panel c; black arrows). Usually, T cells (panel e, white arrowhead) and B cells (panel g; white arrowhead) are negative for activated p38MAPKα (black arrowheads). Activated ERK is present most frequently in macrophages (panel b) and fibroblasts (panel d; simultaneous brown and blue staining, black arrows), whereas it (black arrowheads) is only rarely expressed in T cells (panel g) and B cells (panel h; white arrowheads). Original magnification 1000×. In the lower panels, bars indicate the relative number of cells exhibiting activation of (i) p38MAPKα, (j) ERK and (k) JNK. Analyses were performed for T lymphocytes, B lymphocytes, synovial fibroblasts and macrophages. Activation of p38MAPKα was significantly more frequent in macrophages than in T cells, B cells and fibroblasts (all P < 0.05); activation of ERK was significantly more abundant in macrophages and fibroblasts than in T cells and B cells (P < 0.05). Data are expressed as mean ± standard error of the mean.