Clinical recovery after stroke can be significant and has been attributed to plastic reorganization and recruitment of novel areas previously not engaged in a given task. As equivocal results have been reported in studies using single imaging or electrophysiological methods, here we applied an integrative multimodal approach to a group of well-recovered chronic stroke patients (n = 11; aged 50-81 years) with left capsular lesions. Focal activation during recovered hand movements was assessed with EEG spectral analysis and H2(15)O-PET with EMG monitoring, cortico-cortical connectivity with EEG coherence analysis (cortico-cortical coherence) and corticospinal connectivity with transcranial magnetic stimulation (TMS). As seen from comparisons with age-matched controls, our patients showed enhanced recruitment of the lateral premotor cortex of the lesioned hemisphere [Brodmann area (BA) 6], lateral premotor and to a lesser extent primary sensorimotor and parietal cortex of the contralesional hemisphere (CON-H; BA 4 and superior parietal lobule) and left cerebellum (patients versus controls, Z > 3.09). EEG coherence analysis showed that after stroke cortico-cortical connections were reduced in the stroke hemisphere but relatively increased in the CON-H (ANOVA, contrast analysis, P < 0.05), suggesting a shift of functional connectivity towards the CON-H. Nevertheless, fast conducting corticospinal transmission originated exclusively from the lesioned hemisphere. No direct ipsilateral motor evoked potentials (MEPs) could be elicited with TMS over the contralesional primary motor cortex (iM1) in stroke patients. We conclude that (i) effective recovery is based on enhanced utilization of ipsi- and contralesional resources, (ii) basic corticospinal commands arise from the lesioned hemisphere without recruitment of ('latent') uncrossed corticospinal tract fibres and (iii) increased contralesional activity probably facilitates control of recovered motor function by operating at a higher-order processing level, similar to but not identical with the extended network concerned with complex movements in healthy subjects.

Mast cells (MCs) are key effector cells in allergic reactions. However, the inhibitory mechanism that prevents excessive activation of MCs remains elusive. Here we show that leukocyte mono-immunoglobulin-like receptor 3 (LMIR3; also called CD300f) is a negative regulator of MC activation in vivo. LMIR3 deficiency exacerbated MC-dependent allergic responses in mice, including anaphylaxis, airway inflammation, and dermatitis. Both physical binding and functional reporter assays via an extracellular domain of LMIR3 showed that several extracellular lipids (including ceramide) and lipoproteins were possible ligands for LMIR3. Importantly, MCs were frequently surrounded by extracellular ceramide in vivo. Upon engagement of high-affinity immunoglobulin E receptor, extracellular ceramide-LMIR3 binding inhibited MC activation via immunoreceptor tyrosine-based inhibitory and switch motifs of LMIR3. Moreover, pretreatment with LMIR3-Fc fusion protein or antibody against either ceramide or LMIR3 interfered with this binding in vivo, thereby exacerbating passive cutaneous anaphylaxis. Thus, the interaction between extracellular ceramide and LMIR3 suppressed MC-dependent allergic responses.

The leukocyte mono-Ig-like receptor (LMIR) belongs to a new family of paired immunoreceptors. In this study, we analyzed activating receptor LMIR4/CLM-5 as a counterpart of inhibitory receptor LMIR3/CLM-1. LMIR4 is expressed in myeloid cells, including granulocytes, macrophages, and mast cells, whereas LMIR3 is more broadly expressed. The association of LMIR4 with Fc receptor-␥ among immunoreceptor tyrosinebased activation motif-bearing molecules was indispensable for LMIR4-mediated functions of bone marrow-derived mast cells, but dispensable for its surface expression. Cross-linking of LMIR4 led to Lyn-and Syk-dependent activation of bone marrow-derived mast cells, resulting in cytokine production and degranulation, whereas that of LMIR3 did not. The triggering of LMIR4 and TLR4 synergistically caused robust cytokine production in accordance with enhanced activation of ERK, whereas the co-ligation of LMIR4 and LMIR3 dramatically abrogated cytokine production. Notably, intraperitoneal administration of lipopolysaccharide strikingly up-regulated LMIR3 and down-regulated LMIR4, whereas that of granulocyte colony-stimulating factor upregulated both LMIR3 and LMIR4 in granulocytes. Cross-linking of LMIR4 in bone marrow granulocytes also resulted in their activation, which was enhanced by lipopolysaccharide. Collectively, these results suggest that the innate immune system is at least in part regulated by the qualitative and quantitative balance of the paired receptors LMIR3 and LMIR4.The Ig-like receptors provide positive and negative regulation of immune cells upon recognition of various ligands (1-5). We identified previously leukocyte mono-Ig-like receptors (LMIRs) 2 from a cDNA library of bone marrow-derived mast cells (BMMCs). We (6) and others (7-9) demonstrated that LMIR1/MAIRI (myeloid-associated Ig-like receptor I)/CLM-8 (CMRF-35-like molecules-8) and LMIR2/MAIRII/CLM-4/ DIgR1 (dendritic cell-derived Ig-like receptor 1) are expressed mainly in myeloid cells. The human homolog of LMIR1 is CMRF-35H/IRp60 (inhibitory receptor protein of 60 kDa)/ CD300a (10 -14). The inhibitory effects of LMIR1 on mast cells and eosinophils and the activatory roles of LMIR2 in macrophages have been described recently (6,7,11). In addition to LMIRs, a variety of Ig-like paired receptors are expressed by myeloid cells (2,(15)(16)(17), but the biological significance of a paired receptor remains incompletely understood. Despite the similarity in the extracellular Ig-like domains, a striking structural difference between activating and inhibitory receptors exists in the transmembrane and cytoplasmic regions. In general, the former associate with an immunoreceptor tyrosinebased activation motif (ITAM)-or the related activating motifbearing adaptor transmembrane protein, including DAP10, DAP12, or Fc receptor-␥ (FcR␥), via a positively charged residue in the transmembrane domain, whereas the latter include an immunoreceptor tyrosine-based inhibitory motif (ITIM) in the cytoplasmic domain (1,5,18,19). Cells of the myeloid lineage su...

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Leukocyte mono-Ig-like receptor 3 (LMIR3) is an inhibitory receptor mainly expressed in myeloid cells. Coengagement of FcεRI and LMIR3 impaired cytokine production in bone marrow-derived mast cells (BMMCs) induced by FcεRI crosslinking alone. Mouse LMIR3 possesses five cytoplasmic tyrosine residues (Y241, Y276, Y289, Y303, Y325), among which Y241 and Y289 (Y241/289) or Y325 fit the consensus sequence of ITIM or immunotyrosine-based switch motif (ITSM), respectively. The inhibitory effect was abolished by the replacement of Y325 in addition to Y241/289 with phenylalanine (Y241/189/325/F) in accordance with the potential of Y241/289/325 to cooperatively recruit Src homology region 2 domain-containing phosphatase 1 (SHP)-1 or SHP-2. Intriguingly, LMIR3 crosslinking alone induced cytokine production in BMMCs expressing LMIR3 (Y241/276/289/303/325F) mutant as well as LMIR3 (Y241/289/325F). Moreover, coimmunoprecipitation experiments revealed that LMIR3 associated with ITAM-containing FcRγ. Analysis of FcRγ-deficient BMMCs demonstrated that both Y276/303 and FcRγ played a critical role in the activating function of this inhibitory receptor. Importantly, LMIR3 crosslinking enhanced cytokine production of BMMCs stimulated by LPS, while suppressing production stimulated by other TLR agonists or stem cell factor. Thus, an inhibitory receptor LMIR3 has a unique property to associate with FcRγ and thereby functions as an activating receptor in concert with TLR4 stimulation.