M2 microglia and macrophages drive oligodendrocyte differentiation during CNS remyelination

The lack of therapies for progressive multiple sclerosis highlights the need to understand the regenerative process of remyelination that can follow CNS demyelination. This involves an innate immune response consisting of microglia and macrophages, which can be polarized to distinct functional phenotypes: pro-inflammatory (M1) and anti-inflammatory or immunoregulatory (M2). We found that a switch from an M1- to an M2-dominant response occurred in microglia and peripherally derived macrophages as remyelination started. Oligodendrocyte differentiation was enhanced in vitro with M2 cell conditioned media and impaired in vivo following intra-lesional M2 cell depletion. M2 cell densities were increased in lesions of aged mice in which remyelination was enhanced by parabiotic coupling to a younger mouse and in multiple sclerosis lesions that normally show remyelination. Blocking M2 cell-derived activin-A inhibited oligodendrocyte differentiation during remyelination in cerebellar slice cultures. Thus, our results indicate that M2 cell polarization is essential for efficient remyelination and identify activin-A as a therapeutic target for CNS regeneration.

Role of lipocalin-2-chemokine axis in the development of neuropathic pain following peripheral nerve injury

Lipocalin 2 (LCN2), which is also known as 24p3 and neutrophil gelatinase-associated lipocalin (NGAL), binds small, hydrophobic ligands and interacts with cell surface receptor 24p3R to regulate diverse cellular processes. In the present study, we examined the role of LCN2 in the pathogenesis of neuropathic pain using a mouse model of spared nerve injury (SNI). Lcn2 mRNA levels were significantly increased in the dorsal horn of the spinal cord after SNI, and LCN2 protein was mainly localized in neurons of the dorsal and ventral horns. LCN2 receptor 24p3R was expressed in spinal neurons and microglia after SNI. Lcn2-deficient mice exhibited significantly less mechanical pain hypersensitivity during the early phase after SNI, and an intrathecal injection of recombinant LCN2 protein elicited mechanical pain hypersensitivity in naive animals. Lcn2 deficiency, however, did not affect acute nociceptive pain. Lcn2-deficient mice showed significantly less microglial activation and proalgesic chemokine (CCL2 and CXCL1) production in the spinal cord after SNI than wild-type mice, and recombinant LCN2 protein induced the expression of these chemokines in cultured neurons. Furthermore, the expression of LCN2 and its receptor was detected in neutrophils and macrophages in the sciatic nerve following SNI, suggesting the potential role of peripheral LCN2 in neuropathic pain. Taken together, our results indicate that LCN2 plays a critical role in the development of pain hypersensitivity following peripheral nerve injury and suggest that LCN2 mediates neuropathic pain by inducing chemokine expression and subsequent microglial activation.

Polarization of macrophages and microglia in inflammatory demyelination

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system, and microglia and macrophages play important roles in its pathogenesis. The activation of microglia and macrophages accompanies disease development, whereas depletion of these cells significantly decreases disease severity. Microglia and macrophages usually have diverse and plastic phenotypes. Both pro-inflammatory and antiinflammatory microglia and macrophages exist in MS and its animal model, experimental autoimmune encephalomyelitis. The polarization of microglia and macrophages may underlie the differing functional properties that have been reported. in this review, we discuss the responses and polarization of microglia and macrophages in MS, and their effects on its pathogenesis and repair. Harnessing their beneficial effects by modulating their polarization states holds great promise for the treatment of inflammatory demyelinating diseases.

Inhibition of eosinophils degranulation by Ketotifen in a patient with milk allergy, manifested as bronchial asthma--an electron microscopic study

Electron microscopic studies provided evidence that a patient with cow's milk allergy, manifested as bronchial asthma, has prominent eosinophil granule discharge, attributable to the release of cytotoxic major basic protein (MBP). This finding illustrates a critical role of eosinophil MBP in anaphylactic injury induced by food allergen. Patient white blood cells pretreated with Ketotifen revealed intact ultrastructure of eosinophils granules and cytoplasm. Inhibition of eosinophils degranulation by Ketotifen demonstrates a new pharmacologic mode of action of this anti-allergic, anti-anaphylactic agent.