TNF/LTalpha/LTbeta (tumor necrosis factor/lymphotoxin-alpha/lymphotoxin-beta) triple knockout (KO) mice show a significant reduction of dendritic cell (DC) number in the spleen, presumably due to defective recruitment and/or production. To distinguish between these possibilities, DCs were generated from bone marrow (BM) cultures prepared from wild-type (wt) and mutant mice in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The yield of CD11c(+) major histocompatibility complex (MHC) class II+ DCs generated from TNF/LTalpha/LTP-/- BM culture was significantly reduced compared with wt BM culture. In order to further dissect the individual pathways responsible for defective DC properties observed in TNF/LTalpha/LTP-/- mice, the panel of TNF/LT ligand and receptor single KO mice were used. the production of DCs from BM culture was significantly reduced in TNF-/- and TNF receptor (TNFR) p55(-/-) mice, but normal in LTalpha(-/-), LTbeta(-/-), LTbetaR(-/-) mice. Recombinant TNF (rTNF) exogenously added to TNF/LTalpha/LTbeta(-/-) BM cultures could reverse this defect, and blocking antibodies showed partial effect on BFA cultures of wt mice. Conversely, numbers of mature DCs in spleen were significantly decreased in LTalpha(-/-), LTbeta(-/-), LTbetaR(-/-) mice, but not in TNF-/- and TNFRp55(-/-) mice. These results reveal 2 distinct contributions of fkF/LT cytokines. First, TNF acting through TNF receptor is involved in the development/ maturation of DCs in BM progenitor cultures, but this function appears to be redundant in vivo. Second, the microenvironment in peripheral lymphoid organs associated with LTalpha/LTbeta-LTbetaR Signaling and chemokine production is critical for recruitment efficiency of DCs, and this pathway is indispensable. (C) 2003 by The American Society of Hematology.
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