Natural killer (NK) cells and dendritic cells (DCs) are, respectively, central components of innate and adaptive immune responses. We describe here a third DC lineage, termed interferon-producing killer DCs (IKDCs), distinct from conventional DCs and plasmacytoid DCs and with the molecular expression profile of both NK cells and DCs. They produce substantial amounts of type I interferons (IFN) and interleukin (IL)-12 or IFN-gamma, depending on activation stimuli. Upon stimulation with CpG oligodeoxynucleotides, ligands for Toll-like receptor (TLR)-9, IKDCs kill typical NK target cells using NK-activating receptors. Their cytolytic capacity subsequently diminishes, associated with the loss of NKG2D receptor (also known as Klrk1) and its adaptors, Dap10 and Dap12. As cytotoxicity is lost, DC-like antigen-presenting activity is gained, associated with upregulation of surface major histocompatibility complex class II (MHC II) and costimulatory molecules, which formally distinguish them from classical NK cells. In vivo, splenic IKDCs preferentially show NK function and, upon systemic infection, migrate to lymph nodes, where they primarily show antigen-presenting cell activity. By virtue of their capacity to kill target cells, followed by antigen presentation, IKDCs provide a link between innate and adaptive immunity.

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The neurovascular unit is an emerging concept that emphasizes homeostatic interactions between endothelium and cerebral parenchyma. Here, we show that cerebral endothelium are not just inert tubes for delivering blood, but they also secrete trophic factors that can be directly neuroprotective. Conditioned media from cerebral endothelial cells broadly protects neurons against oxygen-glucose deprivation, oxidative damage, endoplasmic reticulum stress, hypoxia, and amyloid neurotoxicity. This phenomenon is largely mediated by endothelial-produced brain-derived neurotrophic factor (BDNF) because filtering endothelial-conditioned media with TrkB-Fc eliminates the neuroprotective effect. Endothelial production of BDNF is sustained by ␤-1 integrin and integrin-linked kinase (ILK) signaling. Noncytotoxic levels of oxidative stress disrupts ILK signaling and reduces endothelial levels of neuroprotective BDNF. These data suggest that cerebral endothelium provides a critical source of homeostatic support for neurons. Targeting these signals of matrix and trophic coupling between endothelium and neurons may provide new therapeutic opportunities for stroke and other CNS disorders.brain injury ͉ neurodegeneration ͉ neurovascular ͉ stroke

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The fungal pathogen Cryptococcus neoformans has a predilection for the central nervous system (CNS), resulting in devastating meningoencephalitis. At present, it is unclear how C. neoformans traverses the blood-brain barrier (BBB) and causes CNS infection. The present study has examined and characterized the interaction of C. neoformans with human brain microvascular endothelial cells (HBMEC), which constitute the BBB. Adhesion of and transcytosis of HBMEC by C. neoformans was inoculum-and time-dependent and occurred with both encapsulated and acapsulated strains. C. neoformans induced marked morphological changes in HBMEC, for example membrane ruffling, irregular nuclear morphology and swelling of the mitochondria and the ER. These findings suggest that C. neoformans induced actin cytoskeletal reorganization of the host cells. In addition, it was observed that the dephosphorylated form of cofilin was increased during cryptococcal adherence to HBMEC, concomitant with the actin rearrangement. Cryptococcal binding to HBMEC was increased in the presence of Y27632, a Rho kinase (ROCK)-specific inhibitor. Since ROCK activates LIM kinase (LIMK), which phosphorylates cofilin (inactive form), this suggests the involvement of the ROCK!LIMK!cofilin pathway. In contrast, the phosphatase inhibitor sodium orthovanadate decreased adherence of Cryptococcus to HBMEC, concomitant with the increase of phosphorylation of cofilin. Furthermore, the tight junction marker protein occludin became Tritonextractable, indicating alteration of tight junctions in brain endothelial cells. This is the first demonstration that C. neoformans is able to adhere to and transcytose across the HBMEC monolayer and alter the cytoskeleton morphology in HBMEC. Further characterization of the interactions between C. neoformans and HBMEC should help the development of novel strategies to prevent cryptococcal meningitis and its associated morbidity.

Cryptococcal meningoencephalitis develops as a result of hematogenous dissemination of inhaled

Cerebral malaria (CM) is a deadly complication of Plasmodium falciparum infection, but specific interactions involved in cerebral homing of infected erythrocytes (IEs) are poorly understood. In this study, P. falciparum-IEs were characterized for binding to primary human brain microvascular endothelial cells (HBMECs). Before selection, CD36 or ICAM-1-binding parasites exhibited punctate binding to a subpopulation of HBMECs and binding was CD36 dependent. Panning of IEs on HBMECs led to a more dispersed binding phenotype and the selection of three var genes, including two that encode the tandem domain cassette 8 (DC8) and were non-CD36 binders. Multiple domains in the DC8 cassette bound to brain endothelium and the cysteine-rich interdomain region 1 inhibited binding of P. falciparum-IEs by 50%, highlighting a key role for the DC8 cassette in cerebral binding. It is mysterious how deadly binding variants are maintained in the parasite population. Clonal parasite lines expressing the two brain-adherent DC8-var genes did not bind to any of the known microvascular receptors, indicating unique receptors are involved in cerebral binding. They could also adhere to brain, lung, dermis, and heart endothelial cells, suggesting cerebral binding variants may have alternative sequestration sites. Furthermore, young African children with CM or nonsevere control cases had antibodies to HBMEC-selected parasites, indicating they had been exposed to related variants during childhood infections. This analysis shows that specific P. falciparum erythrocyte membrane protein 1 types are linked to cerebral binding and suggests a potential mechanism by which individuals may build up immunity to severe disease, in the absence of CM.cytoadhesion | antigenic variation | parasite ligand

The numbers of immune-activated brain mononuclear phagocytes (MPs) affect the progression of human immunodeficiency virus (HIV)-1-associated dementia (HAD). Such MPs originate , in measure , from a pool of circulating monocytes. To address the mechanism(s) for monocyte penetration across the bloodbrain barrier (BBB) , we performed cross-validating laboratory , animal model , and human brain tissue investigations into HAD pathogenesis. First , an artificial BBB was constructed in which human brain microvascular endothelial and glial cells-astrocytes, microglia , and/or monocyte-derived macrophages (MDM)-were placed on opposite sides of a matrixcoated porous membrane. Second , a SCID mouse model of HIV-1 encephalitis (HIVE) was used to determine in vivo monocyte blood-to-brain migration. Third , immunohistochemical analyses of human HIVE tissue defined the relationships between astrogliosis , activation of microglia , virus infection, monocyte brain infiltration , and ␤-chemokine expression. The results , taken together , showed that HIV-1-infected microglia increased monocyte migration through an artificial BBB 2 to 3.5 times more than replicate numbers of MDM. In the HIVE SCID mice, a marked accumulation of murine MDM was found in areas surrounding virus-infected human microglia but not MDM. For human HIVE , microglial activation and virus infection correlated with astrogliosis, monocyte transendothelial migration , and ␤-chemokine expression. Pure cultures of virus-infected and activated microglia or astrocytes exposed to microglial conditioned media produced significant quantities of ␤-chemokines. We conclude that microglial activation alone and/or through its interactions with astrocytes induces ␤-chemokine-mediated monocyte migration in HAD. (Am J Pathol 1999, 155:1599 -1611)