Bone marrow colony-formation in vitro after infection of genetically defined inbred mice with Candida albicans

Dectin-1 signaling inhibits osteoclastogenesis via IL-33-induced inhibition of NFATc1

Abnormal osteoclast activation contributes to osteolytic bone diseases (OBDs). It was reported that curdlan, an agonist of dectin-1, inhibits osteoclastogenesis. However, the underlying mechanisms are not fully elucidated. In this study, we found that curdlan potently inhibited RANKL-induced osteoclast differentiation and the resultant bone resorption. Curdlan inhibited the expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), the key transcriptional factor for osteoclastogenesis. Notably, dectin-1 activation increased the expression of MafB, an inhibitor of NFATc1, and IL-33 in osteoclast precursors. Mechanistic studies revealed that IL-33 enhanced the expression of MafB in osteoclast precursors and inhibited osteoclast precursors to differentiate into mature osteoclasts. Furthermore, blocking ST2, the IL-33 receptor, partially abrogated curdlan-induced inhibition of NFATc1 expression and osteoclast differentiation. Thus, our study has provided new insights into the mechanisms of dectin-1-induced inhibition of osteoclastogenesis and may provide new targets for the therapy of OBDs.

Effector function of leucocytes from susceptible and resistant mice against distinct isolates of Candida albicans

Neutrophils and macrophages were generated in vitro from mice that display either high or low tissue susceptibilities to Candida albicans infection and their ability to phagocytose and kill three isolates of the yeast with different virulence characteristics was evaluated. In the absence of opsonization, phagocytosis by BALB/c and CBA/CaH neutrophils was comparable, but the killing was very poor. Opsonization with normal serum slightly decreased phagocytosis, but it had markedly different effects on killing, either enhancing or inhibiting candidacidal activity, depending on the combination of yeast isolate and mouse strain. In contrast, BALB/c macrophages showed high levels of phagocytosis and killing of both unopsonized yeasts and opsonized yeasts; whereas killing of unopsonized yeasts by CBA/CaH macrophages was poor, it was markedly enhanced by opsonization.