Extramedullary hematopoiesis of the cranial dura and anhidrotic ectodermal dysplasia

Postmortem Evidence of Brain Inflammatory Markers and Injury in Septic Patients: A Systematic Review

OBJECTIVES

Sepsis is a life-threatening organ dysfunction caused by a host's unregulated immune response to eliminate the infection. After hospitalization, sepsis survivors often suffer from long-term impairments in memory, attention, verbal fluency, and executive functioning. To understand the effects of sepsis and the exacerbated peripheral inflammatory response in the brain, we asked the question: What are the findings and inflammatory markers in the brains of deceased sepsis patients? To answer this question, we conducted this systematic review by the recommendations of Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

DATA SOURCES

Relevant studies were identified by searching the PubMed/National Library of Medicine, PsycINFO, EMBASE, Bibliographical Index in Spanish in Health Sciences, Latin American and Caribbean Health Sciences Literature, and Web of Science databases for peer-reviewed journal articles published on April 05, 2021.

STUDY SELECTION

A total of 3,745 articles were included in the primary screening; after omitting duplicate articles, animal models, and reviews, 2,896 articles were selected for the study. These studies were selected based on the title and abstract, and 2,772 articles were still omitted based on the exclusion criteria.

DATA EXTRACTION

The complete texts of the remaining 124 articles were obtained and thoroughly evaluated for the final screening, and 104 articles were included.

DATA SYNTHESIS

The postmortem brain had edema, abscess, hemorrhagic and ischemic injuries, infarction, hypoxia, atrophy, hypoplasia, neuronal loss, axonal injuries, demyelination, and necrosis.

CONCLUSIONS

The mechanisms by which sepsis induces brain dysfunction are likely to include vascular and neuronal lesions, followed by the activation of glial cells and the presence of peripheral immune cells in the brain.

[A gene study of a family with hidrotic ectodermal dysplasia]

OBJECTIVE

To investigate the clinical features and molecular mechanism of hidrotic ectodermal dysplasia (HED).

METHODS

A clinical and gene study was performed for five generations (91 people) in the family of one proband with HED. GJB6 gene detection was performed for 7 patients and 3 normal people in this family.

RESULTS

Among the 91 people in this family, there were 17 HED patients, who were manifested as having dysplasia of the fingernails and toenails and sparse or absent hair or body hair. The male patients had a greater degree of sparse hair compared with female patients. In the younger generations, damage to the fingernails and toenails was gradually alleviated. There were patients in each generation, the patient's mother or father definitely had this disease. Both males and females developed this disease, and the inheritance pattern was autosomal dominant inheritance. A heterozygous missense mutation, 31G→A, in GJB6 gene was detected in all patients in this family, but this mutation was not detected in family members without the clinical manifestations of HED.

CONCLUSIONS

HED is a hereditary disease with autosomal dominant inheritance and has the clinical features of dysplasia of the fingernails and toenails, hyperkeratosis of palms and soles, and sparse or absent hair or body hair. Male patients have a greater degree of sparse hair. In the younger generations, damage to the fingernails and toenails is gradually alleviated. The missense mutation 31G→A in the GJB6 gene may be one of the molecular mechanisms for HED.

Inherited and acquired immunodeficiencies underlying tuberculosis in childhood

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb) and a few related mycobacteria, is a devastating disease, killing more than a million individuals per year worldwide. However, its pathogenesis remains largely elusive, as only a small proportion of infected individuals develop clinical disease either during primary infection or during reactivation from latency or secondary infection. Subacute, hematogenous, and extrapulmonary disease tends to be more frequent in infants, children, and teenagers than in adults. Life-threatening primary TB of childhood can result from known acquired or inherited immunodeficiencies, although the vast majority of cases remain unexplained. We review here the conditions conferring a predisposition to childhood clinical diseases caused by mycobacteria, including not only M.tb but also weakly virulent mycobacteria, such as BCG vaccines and environmental mycobacteria. Infections with weakly virulent mycobacteria are much rarer than TB, but the inherited and acquired immunodeficiencies underlying these infections are much better known. Their study has also provided genetic and immunological insights into childhood TB, as illustrated by the discovery of single-gene inborn errors of IFN-γ immunity underlying severe cases of TB. Novel findings are expected from ongoing and future human genetic studies of childhood TB in countries that combine a high proportion of consanguineous marriages, a high incidence of TB, and an excellent clinical care, such as Iran, Morocco, and Turkey.

Frequent somatic mosaicism of NEMO in T cells of patients with X-linked anhidrotic ectodermal dysplasia with immunodeficiency

Somatic mosaicism has been described in several primary immunodeficiency diseases and causes modified phenotypes in affected patients. X-linked anhidrotic ectodermal dysplasia with immunodeficiency (XL-EDA-ID) is caused by hypomorphic mutations in the NF-κB essential modulator (NEMO) gene and manifests clinically in various ways. We have previously reported a case of XL-EDA-ID with somatic mosaicism caused by a duplication mutation of the NEMO gene, but the frequency of somatic mosaicism of NEMO and its clinical impact on XL-EDA-ID is not fully understood. In this study, somatic mosaicism of NEMO was evaluated in XL-EDA-ID patients in Japan. Cells expressing wild-type NEMO, most of which were derived from the T-cell lineage, were detected in 9 of 10 XL-EDA-ID patients. These data indicate that the frequency of somatic mosaicism of NEMO is high in XL-ED-ID patients and that the presence of somatic mosaicism of NEMO could have an impact on the diagnosis and treatment of XL-ED-ID patients.

Diagnosis and treatment in anhidrotic ectodermal dysplasia with immunodeficiency

Anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID) is characterized according to its various manifestations, which include ectodermal dysplasia, vascular anomalies, osteopetrosis, and diverse immunological abnormalities such as susceptibility to pathogens, impaired antibody responses to polysaccharides, hypogammaglobulinemia, hyper-IgM syndrome, impaired natural killer cell cytotoxicity, and autoimmune diseases. Two genes responsible for EDA-ID have been identified: nuclear factor-κB (NF-κB) essential modulator (NEMO) for X-linked EDA-ID (XL-EDA-ID) and IκBα for autosomal-dominant EDA-ID (AD-EDA-ID). Both genes are involved in NF-κB activation, such that mutations or related defects cause impaired NF-κB signaling. In particular, NEMO mutations are scattered across the entire NEMO gene in XL-EDA-ID patients, which explains the broad spectrum of clinical manifestations and the difficulties associated with making a diagnosis. In this review, we focus on the pathophysiology of EDA-ID and different diagnostic strategies, which will be beneficial for early diagnosis and appropriate treatment.

The zinc finger domain of IKKγ (NEMO) protein in health and disease

Inhibitor of κB kinase (IKK) gamma (IKKγ), also known as nuclear factor κB (NF-κB) essential modulator (NEMO), is a component of the IKK complex that is essential for the activation of the NF-κB pathway. The NF-κB pathway plays a major role in the regulation of the expression of genes that are involved in immune response, inflammation, cell adhesion, cell survival and development. As part of the IKK complex, IKKγ plays a regulatory role by linking the complex to upstream signalling molecules. IKKγ contains two coiled-coil regions, a leucine zipper domain and a highly conserved zinc finger domain. Mutations affecting IKKγ have been associated with X-linked hypohidrotic ectodermal dysplasia with immune deficiency (HED-ID), with the majority of these mutations affecting the C-terminal region of the protein where the zinc finger is located. The zinc finger of IKKγ is needed for NF-κB activation in a cell- and stimulus-specific manner. The major mechanism by which the zinc finger plays this role appears to be the recognition of polyubiquitinated upstream signalling intermediates. This assertion reinforces the current notion that ubiquitination plays a major role in mediating protein–protein interactions in the NF-κB signalling pathway. Because the zinc finger domain of IKKγ is very likely involved in mediating interactions with ubiquitinated proteins, investigations that look for upstream activators or inhibitors of the IKK complex that bind to and interact with the zinc finger of IKKγ are required to gain a better insight into the exact roles of this domain and into the pathogenesis of HED-ID.

Genetic susceptibility in tuberculosis

The importance of host genetic factors in determining susceptibility to tuberculosis (TB) has been studied extensively using various methods, such as case-control, candidate gene and genome-wide linkage studies. Several important candidate genes like human leucocyte antigen/alleles and non-human leucocyte antigen genes, such as cytokines and their receptors, chemokines and their receptors, pattern recognition receptors (including toll-like receptors, mannose binding lectin and the dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin), solute carrier family 11A member 1 (formerly known as natural resistance-associated macrophage protein 1) and purinergic P2X7 receptor gene polymorphisms, have been associated with differential susceptibility to TB in various ethnic populations. This heterogeneity has been explained by host-pathogen and gene-environment interactions and evolutionary selection pressures. Although the achievements of genetics studies might not yet have advanced the prevention and treatment of TB, researchers have begun to widen their scope of investigation to encompass these practical considerations.

From infectious diseases to primary immunodeficiencies

The field of primary immunodeficiencies has expanded, thanks to the exploration of novel clinical phenotypes and their connection with morbid genotypes, and the subsequent exploration of new patients who have known primary immunodeficiency-defining clinical phenotypes and their connection with novel morbid genotypes. This two-way process is becoming increasingly active, particularly for patients who have infectious diseases in whom the underlying immunologic and genetic causes remain mostly unexplained. The authors review how the exploration of children who have clinical infectious diseases caused by mycobacteria, pneumococcus, and herpes simplex virus recently led to the description of three new groups of primary immunodeficiencies. These three examples justify the continuation of the genetic exploration of novel infectious phenotypes and novel patients who have infections. This challenging process will eventually reap its rewards, to the benefit of patients and their families.

Successful allogeneic hemopoietic stem cell transplantation in a child who had anhidrotic ectodermal dysplasia with immunodeficiency

Anhidrotic ectodermal dysplasia with immunodeficiency is associated with multiple infections and a poor clinical outcome. Hypomorphic mutations in nuclear factor kappaB essential modulator (NEMO)/IkappaB kinase complex and a hypermorphic mutation in inhibitor alpha of nuclear factor kappaB (IkappaBalpha) both result in impaired nuclear factor kappaB activation and are associated with X-recessive and autosomal-dominant forms of anhidrotic ectodermal dysplasia with immunodeficiency, respectively. Autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency is also associated with a severe T-cell phenotype. It is not known whether hematopoietic stem cell transplantation can cure immune deficiency in children with anhidrotic ectodermal dysplasia with immunodeficiency. A boy with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency and a severe T-cell immunodeficiency underwent transplantation at 1 year of age with haploidentical T-cell-depleted bone marrow after myeloablative conditioning. Engraftment occurred, with full hematopoietic chimerism. Seven years after transplantation, clinical outcome is favorable, with normal T-cell development. As expected, the developmental features of the anhidrotic ectodermal dysplasia syndrome have appeared and persisted. This is the first report of successful hematopoietic stem cell transplantation in a child with anhidrotic ectodermal dysplasia with immunodeficiency. Hematopoietic stem cell transplantation is well tolerated and efficiently cures the profound immunodeficiency associated with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency.

Transient hemophagocytosis with deficient cellular cytotoxicity, monoclonal immunoglobulin M gammopathy, increased T-cell numbers, and hypomorphic NEMO mutation

X-linked osteopetrosis, anhydrotic ectodermal dysplasia, and immunodeficiency (XL-O-EDA-ID) is a disorder that is caused by hypomorphic mutations in the nuclear factor kappaB essential modulator (NEMO). These mutations lead to an impaired NF-kappaB activation. In vitro analyses and studies in animal models show that inhibition of NF-kappaB leads to a decrease of cytokine production and T-cell proliferation. Patients classically display poor or delayed inflammatory response to infections. We describe a boy with XL-O-EDA-ID, 1167-1168insC NEMO mutation, and recurrent infections. In early infancy, he experienced hemophagocytosis with transient deficiency of natural killer activity. Increased immunoglobulin M levels in blood resulted from a monoclonal immunoglobulin M gammopathy. Blood T-cell numbers were constantly increased, most probably resulting from a peripheral T-cell expansion. Our observations suggest that patients with hypomorphic NEMO mutations and repeated infections may experience inflammatory dysregulation.

Meningeal tumors of childhood and infancy. An update and literature review

Meningeal derived tumors of the first 2 decades of life are often diagnostically challenging due to the wide morphologic spectrum encountered and the rarity of most individual entities. The 2 most common patterns include the dural/leptomeningeal-based mass and neoplastic meningitis. Both primary and secondary meningeal presentations may occur, either early or late in the course of various meningothelial, mesenchymal, embryonal, glial, hematopoietic, histiocytic, melanocytic, and inflammatory tumors. As in other areas of pediatric pathology, there are significant differences between this patient cohort and adults, differences which will be emphasized in this review.

NF-κB-related genetic diseases

The recent identification of genetic diseases (incontinentia pigmenti, anhidrotic ectodermal dysplasia with immunodeficiency and cylindromatosis) resulting from mutations affecting components of the nuclear factor-kappaB (NF-kappaB) signaling pathway provides a unique opportunity to understand the function of NF-kappaB in vivo. Besides confirming the importance of NF-kappaB in innate and acquired immunity or bone mass control, analysis of these diseases has uncovered new critical roles played by this transcription factor in the development and homeostasis of the epidermis and the proper function of lymphatic vessels. In addition, the identified mutations will help understanding at the molecular level how NF-kappaB is activated in response to cell stimulation.

Human disease resulting from gene mutations that interfere with appropriate nuclear factor-kappaB activation

The nuclear factor (NF)-kappaB family of transcription factors serves vital roles in a wide array of cell functions. An increasing number of human genetic lesions that result in defined disease entities are linked to inappropriate activation of NF-kappaB. The resulting aberrant NF-kappaB function can lead to cellular defects that ultimately impair normal developmental processes, host immune defenses, or both. Molecular defects that lie upstream in cell-signaling pathways and rely upon NF-kappaB activation tend to give a more specific phenotype, whereas those closer to the actual NF-kappaB proteins have broader defects. A detailed study of these diseases can provide insight into the biochemistry of NF-kappaB activation as well as the role of NF-kappaB in human health.

Inherited disorders of NF-kappaB-mediated immunity in man

The transcription factors of the NF-kappaB family play an important role in immunity to infection in animal models. Three human primary immunodeficiencies associated with impaired NF-kappaB signaling were recently described. X-linked recessive anhidrotic ectodermal dysplasia with immunodeficiency (XL-EDA-ID) is caused by hypomorphic mutations in the gene encoding NEMO/IKKgamma, the regulatory subunit of the IkappaB-kinase (IKK) complex. Autosomal dominant EDA-ID (AD-EDA-ID) is caused by a hypermorphic mutation in the gene encoding the inhibitory protein IkappaBalpha. Autosomal recessive immunodeficiency without EDA is caused by mutations in the gene encoding IRAK-4, a kinase acting upstream from the IKK complex in the TIR signaling pathway. The description of the infectious phenotypes associated with these genetic defects has initiated the forward genetic dissection of NF-kappaB-mediated immunity in man.

X-linked ectodermal dysplasia and immunodeficiency caused by reversion mosaicism of NEMO reveals a critical role for NEMO in human T-cell development and/or survival

X-linked ectodermal dysplasia and immunodeficiency (XL-EDA-ID) is an X-linked recessive disease caused by a mutation in the nuclear factor-kappaB (NF-kappaB) essential modulator (NEMO). Here we report an XL-EDA-ID patient with atypical features of very few naive-phenotype T cells and defective mitogen-induced proliferation of peripheral blood mononuclear cells (PBMCs). The patient's NEMO defect was diagnosed by flow cytometric analysis of intracellular NEMO staining. Specific cell lineages (monocytes and neutrophils) expressed reduced levels of NEMO, but 2 populations of T, B, and NK cells were detected with normal and reduced expression of NEMO. Genomic analysis revealed that duplication of a 4.4-kb sequence ranging from intron 3 to exon 6 caused the reduced expression of NEMO. Polymorphism analysis showed that the patient's B- and T-cell lines with reduced and normal expression of NEMO had the same X chromosome, indicating that the somatic mosaicism was not due to fetomaternal transfusion but was most likely due to postzygotic reversion. This XLEDA-ID case adds to our understanding of NEMO biology, indicating that NEMO is critical for T-cell development and/or survival in humans as well as in mice.

Genetic dissection of immunity to mycobacteria: the human model

Humans are exposed to a variety of environmental mycobacteria (EM), and most children are inoculated with live Bacille Calmette-Guérin (BCG) vaccine. In addition, most of the world's population is occasionally exposed to human-borne mycobacterial species, which are less abundant but more virulent. Although rarely pathogenic, mildly virulent mycobacteria, including BCG and most EM, may cause a variety of clinical diseases. Mycobacterium tuberculosis, M. leprae, and EM M. ulcerans are more virulent, causing tuberculosis, leprosy, and Buruli ulcer, respectively. Remarkably, only a minority of individuals develop clinical disease, even if infected with virulent mycobacteria. The interindividual variability of clinical outcome is thought to result in part from variability in the human genes that control host defense. In this well-defined microbiological and clinical context, the principles of mouse immunology and the methods of human genetics can be combined to facilitate the genetic dissection of immunity to mycobacteria. The natural infections are unique to the human model, not being found in any of the animal models of experimental infection. We review current genetic knowledge concerning the simple and complex inheritance of predisposition to mycobacterial diseases in humans. Rare patients with Mendelian disorders have been found to be vulnerable to BCG, a few EM, and M. tuberculosis. Most cases of presumed Mendelian susceptibility to these and other mycobacterial species remain unexplained. In the general population leprosy and tuberculosis have been shown to be associated with certain human genetic polymorphisms and linked to certain chromosomal regions. The causal vulnerability genes themselves have yet to be identified and their pathogenic alleles immunologically validated. The studies carried out to date have been fruitful, initiating the genetic dissection of protective immunity against a variety of mycobacterial species in natural conditions of infection. The human model has potential uses beyond the study of mycobacterial infections and may well become a model of choice for the investigation of immunity to infectious agents.

Osteopetrosis, lymphedema, anhidrotic ectodermal dysplasia, and immunodeficiency in a boy and incontinentia pigmenti in his mother

A child with X-linked osteopetrosis, lymphedema, anhidrotic ectodermal dysplasia, and immunodeficiency (OL-EDA-ID) was recently reported. We report the clinical features of a second boy with this novel syndrome and his mother, who presented with signs of incontinentia pigmenti (IP). The child had mild osteopetrosis without neurosensory complications, unilateral lymphedema of the left leg, and characteristic features of anhidrotic ectodermal dysplasia with sparse hair, facial dysmorphy, delayed eruption of teeth, and sweat gland abnormalities. He died at 18 months of severe immunodeficiency with multiple infections caused by Gram-negative (Salmonella enteritidis) and Gram-positive (Streptococcus pneumoniae) bacteria, nontuberculous mycobacteria (Mycobacterium kansasii), and fungi (Pneumocystis carinii). His 30-year-old mother's medical history, together with residual cutaneous lesions, was highly suggestive of IP without neurologic impairment. In this patient with OL-EDA-ID, we detected the same NF-kappaB essential modulator stop codon hypomorphic mutation identified in the previous patient. The occurrence of the same clinical features in 2 unrelated patients with the same genotype demonstrates that OL-EDA-ID is a genuine clinical syndrome. The clinical and biological descriptions of the proband and his mother further corroborate the relationship between IP and EDA. Both syndromes are allelic and are associated with mutations in NF-kappaB essential modulator, with a genotype-phenotype correlation in hemizygous males. In contrast, loss-of-function mutations and hypomorphic mutations may cause IP in females.

Host susceptibility factors in mycobacterial infection. Genetics and body morphotype

Through identification and evaluation of mutations and polymorphisms in components of the IFN gamma response pathways, a better understanding of the mechanisms and risk factors influencing the development of mycobacterial disease is gained. This may lead the way for development of therapeutic and preventative strategies. Although conventional science has focused on identifying discrete mutations, greater awareness of the impact of subtle changes, both at the genetic (polymorphisms) and physical levels (body morphotype), may prove critical in the investigative process. There has been extraordinary progress in the understanding of mycobacterial susceptibility factors over the last few years. The recognition of characteristic phenotypes will lead to the identification of new genetic bases for disease.

Orbital apex syndrome: a rare presentation of extramedullary hematopoiesis: case report and review of literature

We describe a case of compressive neuropathy in the orbital apex due to extramedullary hematopoiesis (EMH). A 64-year-old man with Polycythemia Rubra Vera developed unilateral visual loss, proptosis, complete ophthalmoplegia, and facial paresis. Bone marrow biopsy showed myelofibrosis. Magnetic resonance imaging demonstrated enhancement at the orbital apex and subtle optic canal narrowing. Decompression of the optic nerve with biopsy of surrounding bone showed EMH. The patient received a course of radiation without benefit. We suggest including the diagnosis of EMH of the orbital apex bones in the differential diagnosis of patients with myeloproliferative disorders who develop an orbital apex syndrome.

Mycobacterial diseases in primary immunodeficiencies

Primary immunodeficiency diseases comprise over 100 conditions, each associated with a variety of viral, bacterial, fungal and protozoan infections. M. tuberculosis and less virulent mycobacteria, such as bacille Calmette-Guérin vaccines and environmental non-tuberculous mycobacteria, may cause severe disease in patients with primary immunodeficiency diseases. However, no previous review has dealt with the issue of which primary immunodeficiency diseases predispose affected individuals to mycobacterial disease. This information is very useful, not only increasing our understanding of human immunity to mycobacteria, but also for the diagnostic investigation of patients with mycobacteriosis. We review here the medical literature on cases of mycobacterial disease in patients with primary immunodeficiency diseases.

Paratracheal extramedullary hematopoiesis

Extramedullary hematopoiesis (EMH) is a rare finding in hematology. A 73-year-old female patient with a 1-week history of severe progressive dyspnea was examined, and computed tomography (CT) showed a paratracheal mass 3 cm in size located 1 cm below the vocals cords and causing obliteration of the tracheal airway. Cytology of a needle biopsy revealed EMH. External radiotherapy of 200-cGy fractions to a total dose of 2000 cGy was administered with 3-dimensional conformal planning to treat the progressive symptoms. The patient's clinical symptoms started to improve 2 days after radiotherapy and had completely disappeared after 7 days. CT scans showed complete response on follow-up at 1 week to 5 months after radiotherapy. Mature and immature hematopoietic cells and many adipose cells were seen in the pretreatment samples. Histologic findings in the posttreatment samples showed that these cells had completely disappeared due to the conformal radiotherapy. On the basis of clinical, radiologic, and histologic results, we suggest that conformal radiotherapy may be useful for the treatment of paratracheal localization of EMH because good tumoral irradiation was obtained in this case, with the protection of normal tissues.

X-linked anhidrotic ectodermal dysplasia with immunodeficiency is caused by impaired NF-kappaB signaling

The molecular basis of X-linked recessive anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID) has remained elusive. Here we report hypomorphic mutations in the gene IKBKG in 12 males with EDA-ID from 8 kindreds, and 2 patients with a related and hitherto unrecognized syndrome of EDA-ID with osteopetrosis and lymphoedema (OL-EDA-ID). Mutations in the coding region of IKBKG are associated with EDA-ID, and stop codon mutations, with OL-EDA-ID. IKBKG encodes NEMO, the regulatory subunit of the IKK (IkappaB kinase) complex, which is essential for NF-kappaB signaling. Germline loss-of-function mutations in IKBKG are lethal in male fetuses. We show that IKBKG mutations causing OL-EDA-ID and EDA-ID impair but do not abolish NF-kappaB signaling. We also show that the ectodysplasin receptor, DL, triggers NF-kappaB through the NEMO protein, indicating that EDA results from impaired NF-kappaB signaling. Finally, we show that abnormal immunity in OL-EDA-ID patients results from impaired cell responses to lipopolysaccharide, interleukin (IL)-1beta, IL-18, TNFalpha and CD154. We thus report for the first time that impaired but not abolished NF-kappaB signaling in humans results in two related syndromes that associate specific developmental and immunological defects.

Extramedullary hematopoiesis in the choroid plexus of five dogs

Five dogs euthanatized because of refractory seizures were found to have hematopoietic elements in the interstitium of the choroid plexus at the level of the fourth ventricle. None of the dogs had significant hematologic or cerebrospinal fluid abnormalities. The extramedullary hematopoiesis was confined to the central nervous system and consisted of megakaryocytes, immature granulocytes, and rubricytes in two dogs and of one predominant cell population in each of the other three dogs. These findings are unique, and factors possibly contributing to the formation of a hematopoietic inductive microenvironment in the choroid plexus are cytokine-neurokine homologies, locally altered vascular supply, and aberrant functioning of bone marrow-derived central nervous system macrophages.