The clinical and immunological patterns of this unique chronic infectious disease clearly demonstrate a continuous scale of changes in histological lesions. Disease classification is defined within two poles (tuberculoid to lepromatous) with transitions between these clinical forms. While typical epithelioid

macrophages predominate at the paucibacillary tuberculoid pole of the disease, inactivated foamy macrophages predominate at the lepromatous end [1]. In lepromatous leprosy (LL), the lack of systemic inflammatory signals and corresponding local ones strongly indicates that a complex anti-inflammatory network is at work. In this regard, neuroendocrine system involvement, in conjunction with the existence of multiple suppressive pathways under the control of the innate and adaptive immune Opaganib datasheet response, has been reported [2-7]. We have suggested that IDO may play a role in a hitherto unknown suppressive mechanism in leprosy [6]. It has also been reported that accumulated oxidized host phospholipids in lepromatous macrophages downregulate the innate immune response [8]. Foamy macrophages seem to sustain intracellular mycobacteria in a physiological state similar to a nonreplicating

vegetative one [9]. In this context, Montoya et al. [10] demonstrated that lepromatous macrophages SRT1720 exhibit a high expression of the cysteine-rich superfamily scavenger receptor (SRCR), which increases the phagocytic capacity of macrophages and leads to a reduction in bactericidal activity. CD163, a receptor only expressed in monocytes and macrophages, is a member of the class B SRCR superfamily with immunomodulatory medroxyprogesterone properties. Likewise, CD163 is a receptor of hemoglobin (Hb) and hemoglobin–haptoglobin (Hp, Hb–Hp) complexes. The metabolites resulting from intracellular Hb degradation exhibit potent antioxidative

and anti-inflammatory effects. It has been described that the binding of Hb to CD163 induces the release of IL-10 and other anti-inflammatory mediators from macrophages in vivo [11]. It has also been demonstrated that IL-10 enhances CD163 expression by creating a feedback arm of regulation [12, 13] and that the CD163 levels in plasma inversely correlate with the expression of CD163 in blood monocytes [14]. In addition, increased CD163 shedding seems to be associated with the immunosuppressive control of inflammation [15]. The role of CD163 as a bacterial sensor has also been proposed, raising the possibility that a different extracellular domain in this receptor is responsible for triggering proinflammatory cytokines, in contrast to what has been considered its traditional endocytic role [16]. Recent reports have demonstrated ongoing interaction between CD163 and IDO in bone marrow-derived dendritic cells (BMDCs), perhaps indicating that different CD163 signals lead to IDO expression [17].