These findings therefore demonstrate that IVIg operates through distinct pathways in naïve mice versus mice in which disease had already been initiated. Nevertheless, the therapeutic function of IVIg still required the inhibitory Fc receptor FcγRIIB [5], suggesting some conserved molecular checkpoints between the preventive and therapeutic modes of actions of IVIg. A possible interpretation for the facultative role of SIGN-R1 in the therapeutic

context could be that a distinct “SIGN-R1-like” receptor is upregulated during the course of the disease. Based on the role of SIGN-R1 in naïve mice, it is tempting to speculate that this role would also be played by a C-type lectin receptor after disease onset. A particularly interesting JAK inhibitor candidate is the dendritic cell immunoreceptor (DCIR), which

was recently identified as a crucial receptor for IVIg in a model of allergic airway disease [29], and is one of the few C-type lectin receptors containing a classical immunoreceptor tyrosine-based inhibitory signaling motif (ITIM) in its intracytoplasmic tail [30]. Noteworthy, the glycan binding specificity of C-type lectins is strongly determined by an amino acid triplet in their carbohydrate recognition domain [31]. These triplets are EPS and EPN for DC-SIGN and DCIR, respectively, suggesting that these receptors might share ligand-binding properties, as indicated by their shared capacity to bind IVIg. The immunosuppressive potential of Rho DCIR is further illustrated by the fact that mice Ivacaftor price deficient in the corresponding gene spontaneously developed autoimmune symptoms typically found in Sjogren’s syndrome, rheumatoid arthritis, or ankylosing spondylitis [32]. Moreover, polymorphisms in the Dcir gene have been associated with rheumatoid arthritis [33]. Further studies will be required to assess the role of DCIR in the

beneficial effect of IVIg in the antibody-driven disease models listed above. Another critical question will be to identify the cell type(s) responsible for the therapeutic effect of IVIg. In this context, the study of Schwab et al. [5] is important because it emphasizes the importance of focusing on a therapeutic rather than a preventive context to dissect the mode of action of IVIg. In this new blueprint, sialic acid on IVIg and FcγRIIB remain essential components of the anti-inflammatory effect, yet the mode of action of IVIg retains some mystery concerning the receptor(s) and cell type(s) targeted. The previous identification of SIGN-R1 and DCIR as key players may facilitate solving these novel enigmas. The laboratory of S.F. is supported by grants from the Deutsche Forschungsgemeinschaft (SFB-650, TRR-36, TRR-130, FI-1238/02), Hertie Stiftung, and an advanced grant from the Merieux Institute.