Ulrike W. Kaunzner

CD11c/EYFP transgene illuminates a discrete network of dendritic cells within the embryonic, neonatal, adult, and injured mouse brain.

The CD11c enhanced yellow fluorescent protein (EYFP) transgenic mouse was constructed to identify dendritic cells in the periphery (Lindquist et al. [ 2004 ] Nat. Immunol. 5:1243–1250). In this study, we used this mouse to characterize dendritic cells within the CNS. Our anatomic results showed discrete populations of EYFP+ brain dendritic cells (EYFP+ bDC) that colocalized with a small fraction of microglia immunoreactive for Mac‐1, Iba‐1, CD45, and F4/80 but not for NeuN, Dcx, NG2 proteoglycan, or GFAP. EYFP+ bDC, isolated by fluorescent activated cell sorting (FACS), expressed mRNA for the Itgax (CD11c) gene, whereas FACS anlaysis of EYFP+ bDC cultures revealed the presence of CD11c protein. Light microscopy studies revealed that EYFP+ bDC were present in the embryonic CNS when the blood–brain barrier is formed and postnatally when brain cells are amenable to culturing. In adult male mice, EYFP+ bDC distribution was prominent within regions of the CNS that 1) are subject to structural plasticity and neurogenesis, 2) receive sensory and humoral input from the external environment, and 3) lack a blood–brain barrier. Ultrastructural analysis of EYFP+ bDC in adult neurogenic niches showed their proximity to developing neurons and a morphology characteristic of immune/microglia cells. Kainic acid‐induced seizures revealed that EYFP+ bDC responded to damage of the hippocampus and displayed morphologies similar to those described for seizure‐activated EGFP+ microglia in the hippocampus of cfms (CSF‐1R) EGFP mice. Collectively, these findings suggest a new member of the dendritic cell family residing among the heterogeneous microglia population. J. Comp. Neurol. 508:687–710, 2008.

Brain dendritic cells in ischemic stroke: time course, activation state, and origin

The immune response to stroke is comprised of inflammatory and regulatory processes. One cell type involved in both innate and adaptive immunity is the dendritic cell (DC). A DC population residing in the healthy brain (bDC) was identified using a transgenic mouse expressing enhanced yellow fluorescent protein (EYFP) under the promoter for the DC marker, CD11c (CD11c/EYFP Tg). To determine if bDC are involved in the immune response to cerebral ischemia, transient (40 min) middle cerebral artery occlusion (MCAO) followed by 6, 24, or 72 h reperfusion was conducted in CD11c/EYFP Tg mice. Our results demonstrated that DC accumulated in the ischemic hemisphere at 24 h post-MCAO-reperfusion, particularly in the border region of the infarct where T lymphocytes accrued. To distinguish resident bDC from the infiltrating peripheral DC, radiation chimeras [1. wild type (WT) hosts restored with CD11c/EYFP Tg bone marrow (BM) or 2. CD11c/EYFP Tg hosts restored with WT BM] were generated and examined by immunocytochemistry. These data confirmed that DC populating the core of the infarct at 72 h were of peripheral origin, whereas those in the border region were comprised primarily of resident bDC. The brain resident (CD45 intermediate) cells of CD11c/EYFP Tg mice were analyzed by flow cytometry. Compared to microglia, bDC displayed increased major histocompatibility class II (MHC II) and co-stimulatory molecules following MCAO-reperfusion. High levels of MHC II and the co-stimulatory molecule CD80 on bDC at 72 h corresponded to peak lymphocyte infiltration, and suggested a functional interaction between these two immune cell populations.

Acute in vivo exposure to interferon-γ enables resident brain dendritic cells to become effective antigen presenting cells

Dendritic cells (DC) are the professional antigen presenting cells (APC) that bridge the innate and adaptive immune system. Previously, in a CD11c/EYFP transgenic mouse developed to study DC functions, we anatomically mapped and phenotypically characterized a discrete population of EYFP+ cells within the microglia that we termed brain dendritic cells (bDC). In this study, we advanced our knowledge of the function of these cells in the CD11c/EYFP transgenic mouse and its chimeras, using acute stimuli of stereotaxically inoculated IFNγ or IL-4 into the CNS. The administration of IFNγ increased the number of EYFP+bDC but did not recruit peripheral DC into the CNS. IFNγ, but not IL-4, upregulated the expression levels of major histocompatibility class II (MHC-II). In addition, IFNγ-activated EYFP+bDC induced antigen-specific naïve CD4 T cells to proliferate and secrete Th1/Th17 cytokines. Activated bDC were also able to stimulate naïve CD8 T cells. Collectively, these data reveal the Th1 cytokine IFNγ, but not the Th2 cytokine IL4, induces bDC to up-regulate MHC-II and become competent APC.

Accumulation of resident and peripheral dendritic cells in the aging CNS

Dendritic cells (DC) are specialized antigen-presenting cells, responsible for peripheral immune responses. Recently, resident brain dendritic cells (bDC) were identified and functionally characterized in the young adult Itgax (CD11c) EYFP+ transgenic mouse brain. In the present study, we describe changes in number, phenotype, and source of bDC in the aging mouse brain. Immunohistochemistry and fluorescent activated cell sorting (FACS) analysis revealed an age-related increase in bDC with a concomitant rise in the expression of immune activation markers MHCII, CD80, and CD86. Quantification of immunolabeled bDC in the cortex, corpus callosum, and cerebellum of the aged brain revealed a 2- to 5-fold increase. In contrast, either no change or a decrease in bDC was noted in regions of adult neurogenesis. Chimeras (wild type host/EYFP+ bone marrow) suggest that the increase of EYFP+ cells in the aging brain is in part due to an accumulation of peripherally derived cells. Collectively, the numerical and phenotypic changes in bDC indicate these cells may serve as an important immune component in the functional and anatomic alterations associated with aging.

Pituitary dendritic cells communicate immune pathogenic signals

This study reveals the presence of dendritic cells (DCs) in the pituitary gland, which play a role in communicating immune activation to the hypothalamic pituitary adrenal (HPA) axis. Using enhanced yellow fluorescent protein (eyfp) expression as a reporter for CD11c, a marker of DCs, we demonstrate anatomically the presence of CD11c/eyfp+ cells throughout the pituitary. Flow cytometric analysis shows that the predominant cellular phenotype of pituitary CD11c/eyfp+ cells resembles that of non-lymphoid DCs. In vivo and in vitro immune challenge with lipopolysaccharide (LPS) stimulates these pituitary CD11c/eyfp+ DCs, but not eyfp(neg) cells, to increase levels of pro-inflammatory cytokines, IL-6, IL-1β, and TNF-α. In vivo analysis of plasma glucocorticoid (GC) and adrenocorticotropic hormone (ACTH) levels at this early phase of the immune response to LPS suggest that pro-inflammatory cytokine production by DCs within the pituitary may activate the release of GCs from the adrenals via ACTH. Pituitary CD11c/eyfp+ cells also express annexin A1 (ANXA1), indicating a role in GC signal attenuation. In summary, our data demonstrate that a resident DC population of the pituitary gland coordinates GC release in the early phase of systemic immune activation, thereby providing an essential immune signaling sentinel for the initial shaping of the systemic immune response to LPS.

Reduction of PK11195 uptake observed in multiple sclerosis lesions after natalizumab initiation

OBJECTIVE The objective of this study is to longitudinally analyze the uptake of [11C]PK11195-PET in multiple sclerosis patients after 3 and 6 months of natalizumab treatment. METHODS Eighteen MS patients, starting treatment with monocloncal anti-VLA-4, were enrolled in a longitudinal PK-PET study. PK uptake was quantified by volume of distribution (VT) calculation using image-derived input function at baseline, 3 and 6 months. Pharmacokinetic quantification was done using a segmented MRI, and selected areas included white matter, gadolinium enhancing lesions, non-enhancing lesions, cortical grey matter and thalamus. VTs of lesions were calculated in reference to each patients white matter (VT ratio=VTr), to consider physiologic variability. RESULTS Test-retest variability was stable for healthy control (HC). Quantification of PK uptake was completed in 18 patients, and baseline uptake was compared to 6-month uptake. After the start of natalizumab VTr significantly decreased in 13 individual enhancing lesions present within 5 patients (p=0.001). Moreover, VTr of the sum of non-enhancing lesions showed a moderate decrease (p=0.03). No longitudinal changes were detected in normal appearing white matter, the thalamus and cortical grey matter. CONCLUSION A reduction in PK11195 uptake was observed in both enhancing and chronic lesions after the start of natalizumab. PK11195 PET can be used as tool to assess the longitudinal change in MS lesions.

Immediate transient thrombocytopenia at the time of alemtuzumab infusion in multiple sclerosis

Background: Alemtuzumab is a monoclonal antibody approved for relapsing-remitting multiple sclerosis (RRMS). Although Immune thrombocytopenia (ITP) has been reported as a secondary autoimmune phenomenon following alemtuzumab infusion, immediate thrombocytopenia during the infusion has not been reported. Objective: We report transient, reversible, self-limiting acute-onset thrombocytopenia during the first course with alemtuzumab. Results and conclusion: In total, 3 of 22 paitents developed mild self-limited bruising associated with a drop in platelet count from their baseline during the intial 5-day course of alemtuzumab. Upon chart review, all 22 patients who received alemtuzumab developed an immediate mostly asymptomatic drop in platelet count which returned to normal within 2 months post-infusion.

MRI in the assessment and monitoring of multiple sclerosis: an update on best practice

Magnetic resonance imaging (MRI) has developed into the most important tool for the diagnosis and monitoring of multiple sclerosis (MS). Its high sensitivity for the evaluation of inflammatory and neurodegenerative processes in the brain and spinal cord has made it the most commonly used technique for the evaluation of patients with MS. Moreover, MRI has become a powerful tool for treatment monitoring, safety assessment as well as for the prognostication of disease progression. Clinically, the use of MRI has increased in the past couple decades as a result of improved technology and increased availability that now extends well beyond academic centers. Consequently, there are numerous studies supporting the role of MRI in the management of patients with MS. The aim of this review is to summarize the latest insights into the utility of MRI in MS.

Defining Disease Activity and Response to Therapy in MS

Opinion statementDisease activity in multiple sclerosis (MS) has classically been defined by the occurrence of new neurological symptoms and the rate of relapses. Definition of disease activity has become more refined with the use of clinical markers, evaluating ambulation, dexterity, and cognition. Magnetic resonance imaging (MRI) has become an important tool in the investigation of disease activity. Number of lesions as well as brain atrophy have been used as surrogate outcome markers in several clinical trials, for which a reduction in these measures is appreciated in most treatment studies. With the increasing availability of new medications, the overall goal is to minimize inflammation to decrease relapse rate and ultimately prevent long-term disability. The aim of this review is to give an overview on commonly used clinical and imaging markers to monitor disease activity in MS, with emphasis on their use in clinical studies, and to give a recommendation on how to utilize these measures in clinical practice for the appropriate assessment of therapeutic response.

A study of patients with aggressive multiple sclerosis at disease onset

Objective Identify aggressive onset multiple sclerosis (AOMS) and describe its clinical course. Methods AOMS patients were identified from a multiple sclerosis (MS) database based on a set of criteria. The subsequent clinical course of AOMS patients was then reviewed with the goal of potentially identifying the best approaches to manage these patients. Results Fifty-eight of 783 (7.4%) patients in the MS database met the criteria for AOMS, and 43 patients who had complete data for the duration of their follow-up were included in the subsequent analysis. The mean duration of the follow-up was 54 months. Thirty-five patients (81%) were started on a conventional first-line agent (injectable therapies for MS). Only two of these 35 patients (5.7%) had no evidence of disease activity. Twenty-two of 35 patients suffering from refractory disease were switched to a more aggressive treatment (natalizumab, rituximab, alemtuzumab, cyclophosphamide). Eight patients were started on aggressive treatment as their initial therapy, and seven of these eight (87.5%) patients showed no evidence of disease activity. Conclusion With recognition of the crucial significance of early optimal treatment during the potential window of opportunity for best long-term outcomes, we describe AOMS within 1 year of disease onset and discuss possible treatment considerations for these patients.