Adipocytokines are mainly adipocyte-derived cytokines regulating metabolism and as such are key regulators of insulin resistance. Some adipocytokines such as adiponectin and leptin affect immune and inflammatory functions. Visfatin (pre-B cell colony-enhancing factor) has recently been identified as a new adipocytokine affecting insulin resistance by binding to the insulin receptor. In this study, we show that recombinant visfatin activates human leukocytes and induces cytokine production. In CD14+ monocytes, visfatin induces the production of IL-1β, TNF-α, and especially IL-6. Moreover, it increases the surface expression of costimulatory molecules CD54, CD40, and CD80. Visfatin-stimulated monocytes show augmented FITC-dextran uptake and an enhanced capacity to induce alloproliferative responses in human lymphocytes. Visfatin-induced effects involve p38 as well as MEK1 pathways as determined by inhibition with MAPK inhibitors and we observed activation of NF-κB. In vivo, visfatin induces circulating IL-6 in BALB/c mice. In patients with inflammatory bowel disease, plasma levels of visfatin are elevated and its mRNA expression is significantly increased in colonic tissue of Crohn’s and ulcerative colitis patients compared with healthy controls. Macrophages, dendritic cells, and colonic epithelial cells might be additional sources of visfatin as determined by confocal microscopy. Visfatin can be considered a new proinflammatory adipocytokine.

The anemia of chronic disease (ACD) is characterized by macrophage iron retention induced by cytokines and the master regulator hepcidin. Hepcidin controls cellular iron efflux on binding to the iron export protein ferroportin. Many patients, however, present with both ACD and iron deficiency anemia (ACD/IDA), the latter resulting from chronic blood loss. We used a rat model of ACD resulting from chronic arthritis and mimicked ACD/IDA by additional phlebotomy to define differing iron-regulatory pathways. Iron retention during inflammation occurs in macrophages and the spleen, but not in the liver. In rats and humans with ACD, serum hepcidin concentrations are elevated, which is paralleled by reduced duodenal and macrophage expression of ferroportin. Individuals with ACD/IDA have significantly lower hepcidin levels than ACD subjects, and ACD/IDA persons, in contrast to ACD subjects, were able to absorb dietary iron from the gut and to mobilize iron from macrophages. Circulating hepcidin levels affect iron traffic in ACD and ACD/IDA and are more responsive to the erythropoietic demands for iron than to inflammation. Hepcidin determination may aid to differentiate between ACD and ACD/IDA and in selecting appropriate therapy for these patients. IntroductionThe anemia of chronic disease (ACD), also termed the "anemia of inflammation," is the most prevalent anemia in hospitalized patients. 1,2 ACD develops in subjects with diseases involving acute or chronic immune activation, such as patients with infections, malignancies, or autoimmune disorders. At least 3 major immunitydriven mechanisms contribute to the anemia of ACD.First, the retention of iron within the mononuclear phagocytic system leads to hypoferremia and subnormal saturation of transferrin, resulting in a limited availability of iron for erythroid progenitor cells or "functional iron deficiency." 1,3,4 Second, cytokines, such as tumor necrosis factor-␣, interferon-␥, and interleukin-1 (IL-1), exert a negative impact on the proliferation and differentiation of erythroid progenitor cells and can induce apoptosis. 5 Third, patients with ACD display an impaired response to erythropoietin (EPO). 6 The functional iron deficiency present in patients with ACD can be complicated by true iron deficiency resulting from chronic blood loss. 7 Differentiation between ACD and ACD/iron deficiency anemia (IDA) is clinically important because iron supplementation is beneficial for ACD/IDA patients but may be deleterious for ACD patients, especially if these subjects have underlying infections or malignancies. 1 In clinical practice, however, differentiating between ACD and ACD/IDA is difficult, as both diseases present with decreased serum iron concentration and transferrin saturation. In addition, ferritin levels are difficult to interpret during inflammation because ferritin expression is induced by both iron overload and inflammatory cytokines. 8 A ratio of soluble transferrin receptor (sTfR)/log ferritin may be useful in distinguishing ACD from ACD/IDA, but the ratio h...

Iron is an essential component of the erythrocyte protein hemoglobin and is crucial to oxygen transport in vertebrates. In the steady state, erythrocyte production is in equilibrium with erythrocyte removal1. In various pathophysiological conditions, however, erythrocyte life span is severely compromised, which threatens the organism with anemia and iron toxicity2,3. Here we identify an on-demand mechanism that clears erythrocytes and recycles iron. We show that Ly-6Chigh monocytes ingest stressed and senescent erythrocytes, accumulate in the liver via coordinated chemotactic cues, and differentiate to ferroportin 1 (FPN1)-expressing macrophages that can deliver iron to hepatocytes. Monocyte-derived FPN1+ Tim-4neg macrophages are transient, reside alongside embryonically-derived Tim-4high Kupffer cells, and depend on Csf1 and Nrf2. The spleen likewise recruits iron-loaded Ly-6Chigh monocytes, but these do not differentiate into iron-recycling macrophages due to the suppressive action of Csf2. Inhibiting monocyte recruitment to the liver leads to kidney and liver damage. These observations identify the liver as the primary organ supporting rapid erythrocyte removal and iron recycling and uncover a mechanism by which the body adapts to fluctuations in erythrocyte integrity.