TNF and arthritic joint disease: Increased formation of osteoclasts was shown for cultures of peripheral blood mononuclear cells from RA patients associated with enhanced myelopoiesis [29] but Li and co-workers [30] demonstrated, using a human TNF-transgenic mice arthritis model, that enhanced osteoclast formation was confined to precursor cells isolated from blood and spleen and that osteoclastogenic potential of bone marrow precursors remained unaffected.