Adherence regulates macrophage signal transduction and primes tumor necrosis factor production

While monocyte/macrophage (M Phi) adherence to a matrix is necessary for di fferentiation and prolonged survival, the effect of adherence on the signal ing mechanisms responsible for M Phi activation is unknown. Lipopolysacchar ide (LPS) activates M Phi by signaling through members of the mitogen activ ated protein kinase (MAPK) family thereby inducing transcription of proinfl ammatory cytokines, such as TNF-alpha. Since adherence has been shown to af fect different activities of various myeloid phagocytes, we investigated wh ether adherence affects intracellular signaling and modulates activation of the M Phi proinflammatory phenotype. We assessed the effect of adherence o n activation of rabbit alveolar M Phi by measuring LPS-induced TNF-alpha mR NA and TNF-alpha secreted product in adherent versus nonadherent cells, in vitro. The effect of adherence on LPS-induced activation of MAPK was assess ed by western analysis using a dual phosphospecific antibody against p38MAP K, p42,44ERK, and p54SAPK. LPS is known to induce activation of NF-kappaB a nd AP-1. Modulation of these two transcription factors by LPS under adheren t versus nonadherent conditions was evaluated by gel-shift analyses. The re sults were that adherent cells treated with LPS, 10 ng/mL or 1 mug/ml, elic ited a 26- and 132-fold increase, respectively, in TNF-alpha production. No nadherent cells did not elicit significant TNF-alpha in response to LPS. Ad herence alone induced significant ERK and AP-1 activation, but did not stim ulate a significant TNF-alpha response and no further activation of ERK and AP-1 was observed with LPS stimulation. Adherence alone did not activate p 38MAPK or NF-kappaB, but primed M Phi for an augmented response to LPS in a ctivation of p38, NF-kappaB and in production of TNF-alpha. We conclude tha t adherence primes M Phi for activation and regulates MAPK signal transduct ion pathways.