Tumor necrosis factor alpha (TNF alpha) is a potent proinflammatory cytokine also involved in cellular differentiation processes. TNF alpha and both of its receptors (TNFR1 and TNFR2) can be co-expressed on the same cell, allowing for local signaling. This study has examined the expression of all components necessary for autocrine cytokine regulation during human hematopoietic, epithelial, and mesenchymal models of cellular differentiation. Macrophage and dendritic differentiation of human peripheral blood monocytes decreased their TNF alpha and TNFR2 expression while increasing the TNFR1 mRNA. In colon epithelial cell lines (HT-29 and Caco-2) TNF alpha-, TNFRI-, and TNFR2-expression was decreased upon differentiation. No changes, however, were seen during human skin keratinocyte differentiation. TNFR1 expression was unchanged in all three mesenchymal lineages (adipogenesis, chondrogenesis, osteogenesis) tested. Differentiation decreases the TNF alpha message in adipocytes and the TNFR2 mRNA in adipocytes and osteocytes. Our results demonstrate that there is no general principle for TNF alpha signaling during conversion of cells from progenitor to a more differentiated phenotype. Paracrine signaling by TNF alpha to orchestrate different cell types during tissue development and remodeling, therefore, probably overrides the autocrine regulation of differentiation by TNF alpha Non-signaling TNF-receptors may protect chondrocytes and osteocytes from the anti-differentiation effects of local TNFa production. (c) 2006 Elsevier Ltd. All rights reserved.