We thank Beatriz Loria and Edith Mabel Horvat for their technical assistance. This work was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), School of Medicine, Buenos Aires University, and Agencia Nacional de Promoción Científica y Tecnológica, Argentina. The authors have no conflicts of interest. “
“The microbial capsular polysaccharide glucuronoxylomannan (GXM) from the opportunistic fungus Cryptoccocus neoformans is able to alter the innate and adaptive immune response through multi-faceted mechanisms of immunosuppression. The ability of GXM to dampen the immune response involves the induction of T cell apoptosis, which is dependent on GXM-induced up-regulation

of Fas ligand (FasL) on antigen-presenting cells. In this study we elucidate the mechanism exploited by GXM to induce up-regulation of FasL.

We demonstrate that (i) the activation of FasL is dependent on find more GXM HSP inhibitor interaction with FcgammaRIIB (FcγRIIB); (ii) GXM induces activation of c-Jun NH2-terminal kinase (JNK) and p38 signal transduction pathways via FcγRIIB; (iii) this leads to downstream activation of c-Jun; (iv) JNK and p38 are simultaneously, but independently, activated; (v) FasL up-regulation occurs via JNK and p38 activation; and (vi) apoptosis occurs via FcγRIIB engagement with consequent JNK and p38 activation. Our results highlight a fast track to FasL up-regulation via FcγRIIB, and assign to this receptor a novel anti-inflammatory

role that also accounts for induced peripheral tolerance. These results contribute to our understanding of the mechanism of immunosuppression that accompanies cryptococcosis. Compounds that interact with the immune system to up-regulate or down-regulate specific aspects of the host response can be classified as immunomodulators or biological response modifiers [1]. Peptides such as cytokines and chemokines are well-known examples of such molecules. Recently, certain polysaccharides of microbial origin have been described as potent immunomodulators with specific activity for both antigen-presenting cells, such as monocytes and macrophages, and Beta adrenergic receptor kinase T cells. To date, relatively few polysaccharides have been identified as immunomodulators [2]. Glucuronoxylomannan (GXM) is the most important component of the Cryptococcus neoformans polysaccharide capsule and is found bound to the fungal cell to form a capsule, or shed in soluble form during growth in vivo and in vitro. GXM interaction with several natural effector cells such as neutrophils, monocytes, macrophages and dendritic cells has been described. Furthermore, monocytes/macrophages show long-lasting storage of GXM in the intracellular compartment. GXM directly affects multiple functions of innate immune cells by reducing major histocompatibility complex (MHC) class II expression [3,4], dendritic cell maturation [5] and proinflammatory cytokine production [6].