Microglial cells in human brain have phenotypic characteristics related to possible function as dendritic antigen presenting cells

DENDRITIC CELLS IN GLIOBLASTOMA TREATMENT: A MODERN VIEW OF THE PROBLEM AND OWN EXPERIENCE

Glioblastoma (GBM) is the most aggressive primary malignant brain tumor in adults. The improvement of the efficacy of GBM treatment is an urgent problem encouraging the development of novel therapeutic strategies, in particular, immunotherapeutic modalities. With more understanding of the intimate interrelationships between the immune system and the mechanisms involved in cancer origin and progression, the skepticism related to the relevance of the immunotherapeutic approaches in the treatment of brain tumors is gradually decreasing. The review discloses the modern concepts on the association between CNS and the immune system. For a long time, CNS was considered as the immunoprivileged site that prevents the effects of immunotherapy in the treatment of brain tumors. Nowadays, these views are reconsidered, which opens the way to the use of immunotherapeutic approaches in GBM treatment. The results of the recent clinical trials on immunotherapy as a supplement to the conventional GBM treatment are considered. Vaccines based on the dendritic cell (DC) technology are regarded as the most promising for this purpose. The preliminary results of the Ukrainian clinical study are also presented and discussed. The results of the international clinical trials as well as our own experience give evidence of the relevance for using DC vaccines in the complex treatment of GBM, which is supported by the increased survival of patients and the safety of vaccine application. It is of high importance that GBM patients with the most unfavorable prognosis can benefit from DC vaccines as a component of the complex treatment. The prospects for immunotherapy in neurooncology are discussed.

A, Gota V, Goda JS. Insight into lipid-based nanoplatform-mediated drug and gene delivery in neuro-oncology and their clinical prospects

Tumors of the Central nervous System (CNS) are a spectrum of neoplasms that range from benign lesions to highly malignant and aggressive lesions. Despite aggressive multimodal treatment approaches, the morbidity and mortality are high with dismal survival outcomes in these malignant tumors. Moreover, the non-specificity of conventional treatments substantiates the rationale for precise therapeutic strategies that selectively target infiltrating tumor cells within the brain, and minimize systemic and collateral damage. With the recent advancement of nanoplatforms for biomaterials applications, lipid-based nanoparticulate systems present an attractive and breakthrough impact on CNS tumor management. Lipid nanoparticles centered immunotherapeutic agents treating malignant CNS tumors could convene the clear need for precise treatment strategies. Immunotherapeutic agents can selectively induce specific immune responses by active or innate immune responses at the local site within the brain. In this review, we discuss the therapeutic applications of lipid-based nanoplatforms for CNS tumors with an emphasis on revolutionary approaches in brain targeting, imaging, and drug and gene delivery with immunotherapy. Lipid-based nanoparticle platforms represent one of the most promising colloidal carriers for chemotherapeutic, and immunotherapeutic drugs. Their current application in oncology especially in brain tumors has brought about a paradigm shift in cancer treatment by improving the antitumor activity of several agents that could be used to selectively target brain tumors. Subsequently, the lab-to-clinic transformation and challenges towards translational feasibility of lipid-based nanoplatforms for drug and gene/immunotherapy delivery in the context of CNS tumor management is addressed.

Immunotherapy for Glioblastoma: Current Progress and Challenge

Glioblastoma is a highly lethal brain cancer with a median survival rate of less than 15 months when treated with the current standard of care, which consists of surgery, radiotherapy and chemotherapy. With the recent success of immunotherapy in other aggressive cancers such as advanced melanoma and advanced non-small cell lung cancer, glioblastoma has been brought to the forefront of immunotherapy research. Resistance to therapy has been a major challenge across a multitude of experimental candidates and no immunotherapies have been approved for glioblastoma to-date. Intra- and inter-tumoral heterogeneity, an inherently immunosuppressive environment and tumor plasticity remain barriers to be overcome. Moreover, the unique tissue-specific interactions between the central nervous system and the peripheral immune system present an additional challenge for immune-based therapies. Nevertheless, there is sufficient evidence that these challenges may be overcome, and immunotherapy continues to be actively pursued in glioblastoma. Herein, we review the primary ongoing immunotherapy candidates for glioblastoma with a focus on immune checkpoint inhibitors, myeloid-targeted therapies, vaccines and chimeric antigen receptor (CAR) immunotherapies. We further provide insight on mechanisms of resistance and how our understanding of these mechanisms may pave the way for more effective immunotherapeutics against glioblastoma.

Immunotherapy and radiation for high-grade glioma: a narrative review

Glioblastoma and other high-grade gliomas (HGGs) are the most common and deadly primary brain tumors. Due to recent advances in immunotherapy and improved clinical outcomes in other disease sites, the study of immunotherapy in HGG has increased significantly. Herein, we summarize and evaluate existing evidence and ongoing clinical trials investigating the use of immunotherapy in the treatment of HGG, including therapeutic vaccination, immune checkpoint inhibition, adoptive lymphocyte transfer, and combinatorial approaches utilizing radiation and multiple modalities of immunotherapy. Special attention is given to the mechanisms by which radiation may improve immunogenicity in HGG, why this motivates the study of radiation in combination with immunotherapy, and how to determine optimal dosing and scheduling of radiation. Though larger randomized controlled trials have not consistently shown improvements in clinical outcomes, this area of research is still in its early stages and a number of important lessons can be taken away from the studies that have been completed to date. Many studies found a subset of patients who experienced durable responses, and analysis of their immune cells and tumor cells can be used to identify biomarkers that predict therapeutic response, as well as additional glioma-specific targets that can enhance therapeutic efficacy in a challenging tumor type.

Parkinson's Disease: Can Targeting Inflammation Be an Effective Neuroprotective Strategy?

The reason why dopamine neurons die in Parkinson’s disease remains largely unknown. Emerging evidence points to a role for brain inflammation in neurodegeneration. Essential questions are whether brain inflammation happens sufficiently early so that interfering with this process can be expected to slow down neuronal death and whether the contribution from inflammation is large enough so that anti-inflammatory agents can be expected to work. Here I discuss data from human PD studies indicating that brain inflammation is an early event in PD. I also discuss the role of T-lymphocytes and peripheral inflammation for neurodegeneration. I critically discuss the failure of clinical trials targeting inflammation in PD.

The Molecular and Microenvironmental Landscape of Glioblastomas: Implications for the Novel Treatment Choices

Glioblastoma (GBM) is the most frequent and aggressive primary central nervous system tumor. Surgery followed by radiotherapy and chemotherapy with alkylating agents constitutes standard first-line treatment of GBM. Complete resection of the GBM tumors is generally not possible given its high invasive features. Although this combination therapy can prolong survival, the prognosis is still poor due to several factors including chemoresistance. In recent years, a comprehensive characterization of the GBM-associated molecular signature has been performed. This has allowed the possibility to introduce a more personalized therapeutic approach for GBM, in which novel targeted therapies, including those employing tyrosine kinase inhibitors (TKIs), could be employed. The GBM tumor microenvironment (TME) exerts a key role in GBM tumor progression, in particular by providing an immunosuppressive state with low numbers of tumor-infiltrating lymphocytes (TILs) and other immune effector cell types that contributes to tumor proliferation and growth. The use of immune checkpoint inhibitors (ICIs) has been successfully introduced in numerous advanced cancers as well as promising results have been shown for the use of these antibodies in untreated brain metastases from melanoma and from non-small cell lung carcinoma (NSCLC). Consequently, the use of PD-1/PD-L1 inhibitors has also been proposed in several clinical trials for the treatment of GBM. In the present review, we will outline the main GBM molecular and TME aspects providing also the grounds for novel targeted therapies and immunotherapies using ICIs for GBM.

Role of AHR in the control of GBM-associated myeloid cells

Glioblastoma (GBM) is an aggressive and incurable brain tumor; its malignancy has been associated with the activity of tumor infiltrating myeloid cells. Myeloid cells play important roles in the tumor control by the immune response, but also in tumor progression. Indeed, GBM exploits multiple mechanisms to recruit and modulate myeloid cells. The Aryl Hydrocarbon Receptor (AHR) is a ligand activated transcription factor implicated in the regulation of myeloid cells. In this review, we will summarize current knowledge on the AHR role in the control of myeloid cells and its impact on GBM pathogenesis.

Immunotherapies for malignant glioma

Glioblastoma multiforme (GBM) is a highly malignant primary brain cancer with a dreadful overall survival and for which treatment options are limited. Recent breakthroughs in novel immune-related treatment strategies for cancer have spurred interests in usurping the power of the patient's immune system to recognize and eliminate GBM. Here, we discuss the unique properties of GBM's tumor microenvironment, the effects of GBM standard on care therapy on tumor-associated immune cells, and review several approaches aimed at therapeutically targeting the immune system for GBM treatment. We believe that a comprehensive understanding of the intricate micro-environmental landscape of GBM will abound into the development of novel immunotherapy strategies for GBM patients.

Enhanced Survival of Porcine Neural Xenografts in Mice Lacking CD1d1, But No Effect of NK1.1 Depletion

Transplantation of embryonic porcine neurons may restore neurological function in patients with Parkinson's disease, if immunological rejection could be prevented. This study was performed to investigate the role of natural killer cells (NK cells) and NK1.1+ T cells (NK T cells) in the rejection of neural xenografts. A cell suspension was prepared from the ventral mesencephalon of 26 – 27-day-old pig embryos, and 2 μl was implanted in the right striata of mutant CD1d1 null (CD1.1-/-) mice, NK1.1-depleted mice, and controls. The CD1.1-/- mice are deficient in NK T cells and the antigen-presenting molecule CD1d1. Graft survival and host responses were determined immunohistochemically using markers for dopamine neurons, CD4-, CD8- cells, microglia, and macrophages. At 2 weeks, the grafts were significantly larger in CD1.1-/- mice, 0.09 ± 0.02 μl (mean ± SEM), compared with controls, 0.05 ± 0.01 μl. There was no significant difference between NK1.1-depleted mice, 0.02 ± 0.01 μl, and controls. At 5 weeks, two grafts were still present in the CD1-/- mice, whereas only scars remained in the controls and in the NK1.1-depleted mice. Immune reactions were strong at 2 weeks and less pronounced at 5 weeks in all groups. Microglial activation was lower in NK-depleted mice than in the controls at 2 weeks. In contrast to organ xenografting, NK1.1+ cells do not seem to be important mediators of the rejection of discordant cellular neural xenografts. However, our results suggest that the antigen-presenting molecule CD1d1 may be involved in the rejection process.

The Microenvironmental Landscape of Brain Tumors

The brain tumor microenvironment (TME) is emerging as a critical regulator of cancer progression in primary and metastatic brain malignancies. The unique properties of this organ require a specific framework for designing TME-targeted interventions. Here, we discuss a number of these distinct features, including brain-resident cell types, the blood-brain barrier, and various aspects of the immune-suppressive environment. We also highlight recent advances in therapeutically targeting the brain TME in cancer. By developing a comprehensive understanding of the complex and interconnected microenvironmental landscape of brain malignancies we will greatly expand the range of therapeutic strategies available to target these deadly diseases.

An update on vaccine therapy and other immunotherapeutic approaches for glioblastoma

Outcome for glioblastoma (GBM), the most common primary CNS malignancy, remains poor. The overall survival benefit recently achieved with immunotherapeutics for melanoma and prostate cancer support evaluation of immunotherapies for other challenging cancers, including GBM. Much historical dogma depicting the CNS as immunoprivileged has been replaced by data demonstrating CNS immunocompetence and active interaction with the peripheral immune system. Several glioma antigens have been identified for potential immunotherapeutic exploitation. Active immunotherapy studies for GBM, supported by preclinical data, have focused on tumor lysate and synthetic antigen vaccination strategies. Results to date confirm consistent safety, including a lack of autoimmune reactivity; however, modest efficacy and variable immunogenicity have been observed. These findings underscore the need to optimize vaccination variables and to address challenges posed by systemic and local immunosuppression inherent to GBM tumors. Additional immunotherapy strategies are also in development for GBM. Future studies may consider combinatorial immunotherapy strategies with complimentary actions.

Immunotherapy coming of age: what will it take to make it standard of care for glioblastoma?

With the recent approval by the FDA of an immunotherapy for prostate cancer and another positive immunotherapy trial in melanoma, immunotherapy may finally be coming of age. So what will it take for it to become part of the standard treatment for glioblastoma? To put this question into perspective, we summarize critical background information in neuro-immunology, address immunotherapy clinical trial design, and discuss a number of extrinsic factors that will impact the development of immunotherapy in neuro-oncology.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Transient expression of MIDC-8 in the normal mouse brain

In this study, we have immunohistochemically characterized the expression of mononuclear phagocyte markers CD14, CD36, CD68, CD204 and MARCO by parenchymal microglia in the developing and adult mouse brain. We further investigated whether these cells express two well-characterized phenotypic markers of dendritic cells: CD205 (DEC-205/NLDC-145) and MIDC-8 antigen. Our results confirm the lack of expression of dendritic cell markers by microglia. We noted that these cells do not appear to express markers associated with monocytes and macrophages during the course of development, but do express CD68 and CD204 antigens in the adult. Unexpectedly, we also noted the transient expression of MIDC-8 antigen on cells within the medial ganglionic eminence and by neuroepithelial cells lining the lateral ventricles and in the medial lemniscus between E15 and E19. We discuss this finding in the context of neural and haematopoietic differentiation.

Immunotherapy for malignant gliomas: emphasis on strategies of active specific immunotherapy using autologous dendritic cells

REVIEW

In this review, we discuss immunotherapy for malignant gliomas.

EMPHASIS

The emphasis is on the novel strategy of active specific immunotherapy using dendritic cells as antigen-presenting cells, especially its theoretical concepts and advantages, specific requirements, critical issues, pre-clinical and early clinical experience. Dendritic cell vaccination is situated in the diversity of other immunotherapeutical approaches.

FURTHER DISCUSSION

Future directions, challenges, and drawbacks will be discussed.

TGF-beta 1 synergizes with GM-CSF to promote the generation of glial cell-derived dendriform cells in vitro

Microglia are often considered a type of tissue macrophages analogous Langerhans' cells, while dendritic cells (DC) can be generated in vitro from cultured microglia in the presence of GM-CSF. In this study, we show that TGF-beta 1, in the presence of GM-CSF, promoted the growth and differentiation of glial cell-derived dendritic cells (GC-DC). TGF-beta 1-driven GC-DC exhibited an immature state reflected by low CD11c expression, augmented endocytosis, and reduced antigen presentation. Expression of Fas was inhibited in GM-CSF+TGF-beta 1-supplemented cell cultures and may relate to a long life span of GC-DC treated with GM-CSF+TGF-beta 1. IL-10 and IL-12 mRNA on GC-DC was not affected upon exposure to GM-CSF alone or to GM-CSF+IFN-gamma, GM-CSF+IL-10 or GM-CSF+TGF-beta 1. In sharp contrast, TGF-beta 1, in the presence of GM-CSF, dramatically up-regulated the expression of TNF-alpha and TGF-beta 1 mRNA. These results demonstrate that TGF-beta 1 seems to play a crucial role in the differentiation, functional skewing, and cytokine profile of GC-DC. TGF-beta 1-driven GC-DC awaits further investigation to facilitate a better understanding of the glia-T cell dialog as well as the pathogenesis and immunotherapy of central nervous system inflammatory and degenerative diseases.

Transforming growth factor beta1 prevents IL-1beta-induced microglial activation, whereas TNFalpha- and IL-6-stimulated activation are not antagonized

Microglia rapidly respond to CNS injury, yet the mechanisms leading to their activation and inactivation remain poorly defined. In particular, few studies have established how interactions between inflammatory mediators affect the innate immune response of microglia. To begin to establish how microglia integrate signals from multiple inflammatory mediators, we examined the effects of interleukin 1beta (IL-1beta), interleukin 6 (IL-6), tumor necrosis factor alpha (TNFalpha), interferon gamma (IFN-gamma), and transforming growth factor beta1 (TGFbeta1) on both newborn and bulk-isolated adult microglia. To assess the functional state of the cells, we assayed the expression of cyclooxygenase 2 (Cox-2), interleukin 6, and tumor necrosis factor alpha, and two protein tyrosine kinases that have been implicated in microglial responses to activational stimuli, HCK and FAK. These studies demonstrated that IL-1beta, TNFalpha, IL-6, but not IFN-gamma increase the expression of Cox-2, whereas they all increase the expression of HCK and FAK. In these studies, TGFbeta1 either had no effect, or it decreased basal levels of these proteins. TGFbeta1 blocked activation by IL-1beta when given prior to, or simultaneously with, IL-1beta. TGFbeta1 blocked the induction of the tyrosine kinases, Cox-2, and the induction of IL-6 and TNFalpha mRNAs. However, TGFbeta1 was ineffective in antagonizing the induction of Cox-2 by either IL-6 or TNFalpha. We conclude that the TGFbeta receptor signaling cascades intersect with IL-1, but they may not interact with IL-6 or TNFalpha signaling pathways that lead to activation.

TGF-beta1-conditioned glial cell-derived dendritic cells inhibit expansion of MBP-reactive T cells in vitro

Resident microglial cells contribute to activation and expansion of T cells under inflammatory conditions within the CNS. However, there is no evidence how interactions between microglia and T cells affect CNS inflammation. We evaluated the effect of glial cell-derived dendritic cells (GC-DC) in expanding and eliminating myelin basic protein (MBP)-reactive T cells. GC-DC untreated with TGF-beta1 (GC-DC0) primed antigen specific T cell proliferation, whereas GC-DC treated with TGF-1 (GC-DCbeta) effectively inhibited expansion of T cells via inducing IFN-y-expressing CD8+ T cells. Augmented IFN-gamma and/orTNF-alpha might also affect the elimination of MBP-reactive T cells. These results indicate that TGF-beta1-mediated functional skewing of GC-DC plays a critical role for the elimination of MBP-reactive T cells.

Microglia in diseases of the central nervous system

Microglia (MG) are enigmatic cells of the central nervous system (CNS). MG are morphologically, antigenically and functionally flexible, and have the potential for mobility and proliferation. MG are professional antigen-presenting cells and constitute part of the local CNS innate immune system, communicating with other immune cells via chemokines, cytokines and growth factors. MG contain several antigenic and functional markers similar to macrophages and dendritic cells (DCs), but also present several differences from DCs. The exact role(s) played by MG in the normal human CNS is the topic of lively debate. MG participate in many reactive processes in the CNS and are therefore an integral part of lesions in a variety of pathologic conditions. It is thought that MG may exacerbate diverse neurological conditions, including viral encephalitis, AIDS, Multiple Sclerosis (MS) and Alzheimer's disease. A recurrent theme is the perpetuation by MG of pathological cycles of monocyte recruitment, activation and cytopathic secretions, and/or auto antigen presentation.

Localization of matrix metalloproteinase 1 in cholesteatoma and deep meatal skin

HYPOTHESIS

Matrix metalloproteinase 1 (MMP-1) is overexpressed in cholesteatoma.

BACKGROUND

Cholesteatoma destroys bone, whereas deep meatal skin does not. MMP-1 is a type I collagenase that may be responsible for this destruction. This prospective study was designed to identify overexpression of MMP-1 by cholesteatoma in comparison with deep meatal skin.

METHODS

Ten cholesteatoma specimens and nine deep meatal skin specimens were removed during otologic surgery and then fixed in formalin and embedded in paraffin. Immunocytochemistry studies were performed using a monoclonal antibody to MMP-1. A pathologist assessed the slides in a blinded fashion. Expression of MMP-1 protein in epidermis and in stroma was scored from 0 to 10. Five further cholesteatoma specimens and three deep meatal skin specimens underwent reverse transcriptase polymerase chain reactions to assess messenger ribonucleic acid production. Paired and unpaired Student's t tests were used to assess the difference in expression levels.

RESULTS

Cholesteatoma stroma expressed significantly more MMP-1 protein than did deep meatal skin stroma (p = 0.04). MMP-1 was localized to stromal fibroblasts. There was no difference in the epidermal expression levels of the two tissue types (p = 0.42). The reverse transcriptase polymerase chain reaction showed expression at the messenger ribonucleic acid size of MMP-1 (262 base pair) in all cholesteatoma specimens examined. One deep meatal skin specimen showed a weak signal; no signal was seen in the other specimens.

CONCLUSIONS

MMP-1 is overexpressed by the stromal fibroblasts present in cholesteatoma as compared with deep meatal skin. It is possible that these cells rather than the keratinocytes are responsible for bone destruction in this disease.

CD1 expression is differentially regulated by microglia, macrophages and T cells in the central nervous system upon inflammation and demyelination

Expression of CD1 by microglia, macrophages and T cells was investigated ex vivo. In the healthy central nervous system (CNS), resident microglia, macrophages and T cells express levels of CD1 significantly lower than that expressed by splenic macrophages and T cells. During experimental autoimmune encephalomyelitis (EAE), CD1 expression by microglia and the number of CD1+ microglia increase. Macrophages and T cells strongly upregulate CD1 expression in the CNS, but not in the spleen. Whereas the function of CD1 expressed by T cells remains unclear, the expression by microglia and macrophages provides the CNS with a (glyco)lipidic-presenting molecule in an inflammatory and demyelinating environment.

Lentivirus and foamy virus vectors: novel gene therapy tools

The aim of gene therapy is to modify the genetic material of living cells to achieve therapeutic benefit. Gene therapy involves the insertion of a functional gene into a cell, to replace an absent or defective gene, or to fight an infectious agent or a tumour. At present, a wide variety of somatic tissues are being explored for the introduction of foreign genes with a view towards treatment. A prime requirement for successful gene therapy is the sustained expression of the therapeutic gene without any adverse effect on the recipient. A highly desirable vector would be generated at high titres, integrate into target cells (including non-dividing cells) and have little or no associated immune reactions. Lentiviruses have the ability to infect dividing and non-dividing cells and, therefore, constitute ideal candidates for development of vectors for gene therapy. This review presents a description of available lentiviral vectors, including vector design, applications to disease treatment and safety considerations. In addition, general aspects of the biology of lentiviruses with relevance to vector development will be discussed. Recent investigations have revealed that foamy viruses, another group of retroviruses, are also capable of infecting non-dividing cells. Thus, foamy virus vectors are actively being developed in parallel to lentivirus vectors. This review will also include various aspects of the biology of foamy viruses with relevance to vector development.

Neurotrophins and the anti-inflammatory agents interleukin-4 (IL-4), IL-10, IL-11 and transforming growth factor-beta1 (TGF-beta1) down-regulate T cell costimulatory molecules B7 and CD40 on cultured rat microglia

Microglia are essential for T cell activation in the CNS. Since T cell activation requires costimulation by B7 and/or CD40, we examined the regulation by cytokines of B7-1, B7-2 and CD40 mRNA expression in cultured rat microglia in serum-free medium. All three ligands are expressed constitutively, but are profoundly up-regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF). By contrast, interferon-gamma raises only B7-2 and CD40 mRNA, and the B7-2 increase is inhibited by IL-10. IL-4, transforming growth factor-beta1, and nerve growth factor (NGF) repress GM-CSF-induced B7-2 and CD40, but not B7-1. NGF also down-regulates its own high-affinity trkA receptor. IL-11, unrecognized for its effect on antigen presentation, represses GM-CSF-induced B7-2.

Transforming growth factor-beta1 in adult human microglia and its stimulated production by interleukin-1

Ameboid microglia express human immunodeficiency virus 1 (HIV-1) more frequently than do ramified microglia. These two microglial subtypes might also differ in the frequency with which they express transforming growth factor-beta1 (TGF-beta1), a cytokine that regulates HIV-1 expression in monocytes. Results described here show that ameboid and ramified microglia express TGF-beta1. In brain tissues from HIV-1-infected individuals as compared with seronegative controls, ameboid rather than ramified microglia more frequently expressed TGF-beta1. Ameboid microglia, isolated and cultured from postmortem adult human brain more frequently expressed TGF-beta1 in presence of interleukin-1(IL-1), a cytokine that is elevated in brains of HIV-1-infected individuals when compared with seronegative controls. The stimulation of TGF-beta1 by IL-1 was dose and time dependent, occurring with ameboid microglia isolated from either frontal cortex or globus pallidus but not midbrain pons. Ameboid microglia are similar to the RCA-1-positive cells that form clusters, called microglial nodules, in the brain of HIV-1-infected individuals. Pathologic conditions, such as disseminated microglial nodules, are associated with HIV-1 encephalitis, direct infection of the brain, and moderate to severe neurologic impairment. TGF-beta1 expression in ameboid microglia may play a role in HIV-1 neuropathogenesis.

Enriched immune-environment of blood-brain barrier deficient areas of normal adult rats

The circumventricular organs (CVOs) in the brain are without a blood-brain barrier (BBB) and as such directly exposed to blood plasma constituents and blood-borne pathogens. In light of previous studies showing discrepancies regarding the immunocompetence of these organs, we initiated the present study to provide a comprehensive immunohistochemical analysis of the cellular expression of immune-associated antigens within the pineal gland, area postrema and the subfornical organ. In all CVOs, subpopulations of cells morphologically similar to complement receptor type 3 immunoreactive microglial/macrophage cells expressed major histocompatibility complex (MHC) class II antigen, leucocyte common antigen (LCA/CD45), as well as CD4 and ED1 antigen. Based on morphological criteria the MHC class II antigen expressing cells could be grouped into a major population of classical parenchymal and perivascular ramified microglial cells and a minor population presenting itself as scattered or small groups of rounded macrophage-like cells. CD4 and ED1 antigen were expressed by both cell types. CD45 was preferentially expressed by macrophage-like cells. MHC class I antigen was expressed by the vascular endothelium in both BBB-protected and BBB-deficient areas and was additionally present as a lattice-like network throughout the BBB-deficient parenchyma in all CVOs. The results suggest that the BBB-free areas of the brain besides being constantly surveyed by blood-borne macrophages, possess an intrinsic immune surveillance system based on resting and activated microglial cells, which may function as a non-endothelial, cellular barrier against blood-borne pathogens.

Heterogeneity of antigen expression and lectin labeling on microglial cells in the olfactory bulb of adult rats

Microglia in different layers of the rat olfactory bulb expressed a variety of membrane antigens except for CD4 (OX-35). Bulb microglial cells bearing complement receptor type 3 (OX-42) were ubiquitous and their immunoreactivity varied considerably in different bulb layers. Although very few in number, labeled microglia in all layers also expressed major histocompatibility complex class I antigen (OX-18), leukocyte common antigen (OX-1) and unknown macrophage antigen (ED-2). The latter was localized in cells distributed almost exclusively in the perivascular spaces. The immunoreactivity of ED-1, an unknown cytoplasmic or lysosomal membrane antigen in macrophages, was localized in labeled microglia which were concentrated mainly in the granule cell layer and periglomerular zone of the bulb. A variable number of microglial cells were stained with OX-6 (major histocompatibility complex class II antigen) and they were located predominantly in the periglomerular zone and at the junction between the granule cell layer and the subependymal layer. Ultrastructural study using GSA I-B4 lectin labeling showed that microglia in different layers of the bulb exhibited similar labeling patterns in their subcellular structures. A remarkable feature was the occurrence of some microglia in the olfactory nerve layer, subependymal layer and granule cell layer adjacent to the subependymal layer in which the cells showed intense lectin labeling at their Golgi apparatus, a feature which was absent in microglia of other bulb layers. Present results showed the regional differences in microglial antigen expressions and lectin labeling within the olfactory bulb. It is therefore suggested that the cells subserve very different specific functions depending on their ambient microenvironments. The heterogeneity of microglial functions in the olfactory bulb may be related to the progressive regeneration and degeneration of its containing neurons.

CD1b is expressed in multiple sclerosis lesions

Recent observations have shown that CD1 molecules act as restriction elements in the presentation of antigens to specialized subsets of T cells. To examine the expression of CD1 molecules in multiple sclerosis (MS) lesions, frozen sections of central nervous system (CNS) tissues from nine MS and three other neurological disease (OND) patients, one patient with Wilson's disease, and one non-neurological control were stained by immunocytochemistry. In chronic-active MS lesions, CD1b immunoreactivity was prominent on perivascular inflammatory cells whereas macrophages within the lesion showed little reactivity. At the lesion edge, intense immunoreactivity for CD1b was found on hypertrophic astrocytes. High level expression of CD1b in MS lesions was found to colocalize with the presence of GM-CSF in astrocytes. In chronic-silent lesions, CD1b expression was found on only a few perivascular astrocytic foot processes and the occasional perivascular macrophage. CD1b was not found in the tissues studied for control purposes. In contrast, MHC class II expression was detected on microglia in all tissues examined. The relatively low level expression of CD1b in normal-appearing tissues, chronic-silent lesions and in the OND controls supports the conclusion that the expression of CD1b in active MS lesions is significantly upregulated and could contribute to lesion development.

Mouse microglial cell lines differing in constitutive and interferon-gamma-inducible antigen-presenting activities for naive and memory CD4+ and CD8+ T cells

We developed a panel of non-virus transformed cell lines derived from individual microglial precursors residing in the brains of normal mice. These colony stimulating factor-1-dependent cell lines are B7-1+ (CD80), Mac-1+, Mac-2+, Mac-3+, CD45+, MHC class I+, colony stimulating factor-1 receptor+, and they ingest antibody-coated particles. However, the cell lines differ in their expression of B7-2 (CD86), F4/80, Ly-6C and MHC class II molecules. They also differ in their ability to constitutively process and present antigens to naive CD4+ and CD8+ T cells, memory CD4+ and CD8+, and in the manner by which interferon gamma modulates their antigen-presenting activities. These cell lines should be valuable as models for studies on the immunobiology of the microglia.

Chronic encephalitis associated with epilepsy: immunohistochemical and ultrastructural studies

Chronic encephalitis has been recognized as a cause of epilepsy since the work of Rasmussen et al. in the late 1950s. Despite this, few immunohistochemical studies of the affected brain tissue have been attempted. We have studied specimens of brain tissue from seven patients with this condition who underwent therapeutic multilobar cortical resection or hemispherectomy. Immunohistochemical studies were carried out using antibodies to glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA, PC10), T lymphocytes (UCHL-1), B lymphocytes (L26), macrophages and microglia (HAM-56), and major histocompatibility complex molecules (LN3 and beta 2-microglobulin). Additionally, the results of preliminary immunohistochemical and ultrastructural investigation of possible immune complex deposition in blood vessel walls of affected brain tissue are presented. The pattern of GFAP immunoreactivity suggested a patchy and/or laminar disease process in most patients. GFAP immunoreactive cells were especially prominent around microvessels in some cases, suggesting an abnormality and perivascular collections of inflammatory cells, seen to a variable extent in all cases, contained abundant cells immunolabelled with UCHL-1, LN3 and beta 2-microglobulin. L26-labelled B lymphocytes were extremely sparse. Anti-PCNA frequently labelled microvascular endothelial cells, rare pericytes and occasional cells with microglial/macrophage morphology. The data suggest that chronic encephalitis found in patients with epilepsy results from patchy but widespread parenchymal brain injury, in the course of which cells of both microglial and lymphocyte series accumulate or proliferate within brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional variations of urokinase-type plasminogen activator in human colorectal cancer: a quantitative study by image analysis

Qualitative histological studies in the distribution of urokinase-type plasminogen activator (uPA) in human colorectal carcinomas have been well documented. However, to our knowledge the histological distribution of this enzyme has not been quantified in any tumour. For the present image analysis study, uPA was demonstrated in sections of human colorectal cancer using immunoperoxidase technique. A total of 9 colorectal carcinoma cases were used, in which 132 regions were analysed. Within each region, staining intensity measurements were made at evenly spaced intervals. Samples of normal mucosa from 6 cases were also studied. Enzyme levels were assessed with staining intensity measurements. For each section, a negative control section was included, in which the primary antibody was omitted. Staining for uPA was quantified for each region in the test section, and the measurement for the corresponding region of the negative control was then subtracted. The enzyme uPA was localised more at the tumour edge than in the tumour centre or distant host tissue. These differences were highly significant (p < 0.0001). There was also a highly significant difference in staining intensity when tumour regions adjacent to pushing edge were compared with those adjacent to infiltrating edge (p < 0.0001). Infiltrating tumours showed stronger staining for uPA than tumours with pushing edges. Since invasive activity is thought to be maximal at the edge of the tumour, localisation of uPA at this site is consistent with the role of this enzyme in the process of tumour invasion.

Microglial chimaerism in human xenografts to the rat brain

Neural tissue from human fetuses is currently used for intracerebral transplantation to treat patients with Parkinson's disease. The development of the human fetal tissue following grafting has been considered mostly, up to now, from the neuronal point of view in xenografts. Very little is known, in contrast, about nonneuronal, glial, or vascular cells in the grafts. Comparison of the data gathered on the development of grafted human neurons with those obtained in comparable studies using rat transplants has demonstrated species-specific features. We have therefore undertaken a series of studies dealing with nonneuronal cells in human-to-rat transplants to reveal other possible species-specificity of the human tissue. This study has, accordingly, been devoted to the immunohistochemical analysis of microglia of host and donor origins in a human to rat xenograft paradigm allowing clear distinction of the origin of the cells. Human neural tissue was transplanted as a cell suspension into the thalamus of adult rats. Amoeboid human microglia were observed in 1-, 2-, and 3-month-old transplants, but their density, already relatively low at the first stage, decreased further over time. Ramified human microglia were only occasional. In sharp contrast, host rat microglia rapidly invaded the transplant in the absence of any sign of necrosis. The rat cells exhibited first an amoeboid morphology but progressed at the later stages toward a more mature, ramified morphology. These results indicate that donor microglia are quite few in number at first and, at least, do not proliferate actively after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Transitory disappearance of microglia during the regeneration of the lizard medial cortex

In normal lizards, microglial cells populate the medial cortex (a zone homologous to the hippocampal fascia dentata), with a preferential distribution along the border between the granular cell layer and the plexiform layers. Intraperitoneal injection of the neurotoxin 3-acetylpyridine (3AP) induces a selective lesion in the medial cortex with a rapid degeneration of the granular layer and its zinc-enriched axonal projection. Within 6-8 weeks, the granular layer is, however, repopulated by a new set of neurons generated in the subjacent ependyma and the cell debris is removed. The aim of this study was to determine to what extent microglia were involved in the scavenging processes during the regeneration process. To this end we studied the brains of regenerating lizards at different times after 3AP lesion, visualising microglial cells by the nucleoside diphosphatase (NDPase) histochemical reaction. Surprisingly, we found that stained microglial cells disappeared 6-8 hours after 3AP injection and remained absent until 10-15 days after injection. One month postlesion an increased population of microglial cells was found scattered throughout all plexiform layers of the cortex. Thorough examination of semithin and ultrathin sections confirmed the absence of microglia in the medial cortex of recent lesioned animals but the presence of an exuberant population after 1 month postlesion. In the tissue, phagocytotic scavenging was carried out by radial ependymocytes, not by microglia.

Cervical lymphoid tissue but not the central nervous system supports proliferation of virus-specific T lymphocytes during coronavirus-induced encephalitis in rats

The CD4+ T lymphocyte response in the central nervous system (CNS) and cervical lymph nodes (CLNs) of rats with different susceptibility to coronavirus-induced encephalitis was investigated. The majority of CD4+ T lymphocytes entering the virus-infected CNS in the course of the infection are primed cells that neither proliferate ex vivo nor can be stimulated to proliferation by viral antigens or mitogen in vitro. In contrast, T lymphocytes taken from CLNs of the same animals revealed a strong proliferative response. Restimulation of CLN lymphocytes by viral antigens disclosed a striking difference between the disease-resistant rat strain Brown Norway (BN) and the susceptible Lewis (LEW) strain. Whereas BN lymphocytes responded as early as 5 days post infection, it took more than 11 days until a comparable proliferation was detectable in LEW lymphocytes. From these data we postulate that the majority of T lymphocytes entering the virus-infected brain after sensitisation and expansion in cervical lymph nodes is unresponsive to further proliferation signals and that the kinetics and magnitude of T lymphocyte stimulation in CLNs play an important role in the clinical course of the infection.

Dendritic cells infected in vitro with human T cell leukaemia/lymphoma virus type-1 (HTLV-1); enhanced lymphocytic proliferation and tropical spastic paraparesis

Evidence supporting a role of the dendritic cell (DC) in stimulating autologous T cell activity in tropical spastic paraparesis (TSP) was sought by studies of cells taken from healthy volunteers and exposed to HTLV-1 in vitro. DC were co-cultured with an HTLV-1-producing cell line (MT-2) at 1:1 or 10:1 ratios. These DC stimulated high levels of proliferation in autologous T cells. This was similar to that seen in an autologous mixed leucocyte reaction (AMLR) using cells from TSP patients. The requirement for both DC and virus was confirmed, since neither DC co-cultured with uninfected MT-2 cells nor addition of infected MT-2 cells directly to T cells caused significant stimulation. DC exposed to the highest dose of HTLV-1 (1:1) for 24 h before addition of T cells caused strong stimulation that increased after 8 h but almost disappeared by 72 h. In situ hybridization showed that approximately 25% of DC became infected in cultured cells after preincubation for 24 h, and over 50% were infected with a 72-h preincubation. We suggest that infection of DC by HTLV-1 may be an initial step in altering the immune system in seronegative patients, and that persistent T cell stimulation in those with genetic susceptibility may underlie the production of neurological disease.

Distribution of cell adhesion molecules in skeletal muscle from patients with systemic lupus erythematosus

OBJECTIVE

To investigate the pathophysiology of perivascular mononuclear cell infiltrates observed in skeletal muscle from patients with systemic lupus erythematosus (SLE).

METHODS

Immunocytochemical techniques were used to examine frozen 5 microns sections from the quadriceps needle muscle biopsy specimens of 14 patients with SLE (including seven with infiltrates) for the expression of the cytokine inducible adhesion molecules intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin.

RESULTS

Vessels in 6/7 SLE biopsy specimens with perivascular infiltrates expressed VCAM-1 at a density of > 2 vessels/mm2 in contrast with 0/7 SLE biopsy specimens without infiltrates and 1/6 control specimens. In contrast, E-selectin expression was increased ( > 0.3 positive vessels/mm2) in SLE biopsy specimens compared with control tissue regardless of the presence of perivascular infiltration. VCAM-1 and ICAM-1 were also noted on extravascular cells in the infiltrates, being particularly prominent on the intermuscle fibre dendritic processes of CD68+ HLA-DR+ cells.

CONCLUSION

Expression of these cytokine inducible adhesion molecules may be important in the migration of mononuclear cells into skeletal muscle and may be involved in intercellular interactions within the tissue.

Human retinal microglia express phenotypic characteristics in common with dendritic antigen-presenting cells

Neural tissue has been considered to be immunologically privileged and major histocompatibility complex (MHC) class II antigens not expressed in normal human brain grey matter and retina. In the present study we compare phenotypic characteristics of human retinal microglia and dendritic Langerhans cells, including their morphologies and distribution, MHC class II and CD45 antigen expression and nucleotidase reactivity. Levels of class II expression were measured using optical densitometry in combination with standard immunohistochemical techniques applied to retinal flatmounts. The results indicate that ramified retinal microglia have features in common with dendritic antigen presenting cells of cornea and conjunctivum, including the constitutive expression of MHC class II antigens.

Role of Langerhans cells and other dendritic cells in viral diseases

Langerhans cells are part of a vast system of potent antigen-presenting cells known under the name of dendritic cells. During the last decade, much has been learned on dendritic cell involvement in the immune response to infectious diseases. This review briefly summarizes our current understanding of the role played by Langerhans cells and other dendritic cells in the pathogenesis of DNA and RNA virus infections. These data may form the basis for the development of innovative approaches in the diagnosis, prevention, and treatment of viral diseases.

Microglia and the developing olfactory bulb

The developmental appearance of microglia in the rat olfactory bulb was investigated through the use of selective staining with the B4-isolectin from Griffonia simplicifolia. No changes in the density or distribution of either the spherical, macrophage "ameboid" form or the highly arborized "ramified" variety of microglia were observed in the superficial layers of the bulb between postnatal days 10 and 30. The subependymal zone exhibited the only substantial population of ameboid cells and the only developmental increases in ramified cell density during this time-period. External single naris closure, which enhances cell death in the ipsilateral bulb, did not affect microglia density, presumably due to the unusually high numbers of microglia normally present in the bulb. The olfactory bulb has a dense and relatively uniform population of microglial cells from very early stages of postnatal life, perhaps because of the constant turnover of cells and processes.

Infection of dendritic cells with HIV1: virus load regulates stimulation and suppression of T-cell activity

Patients with HIV infection show two major types of immunological effects. The first is hyperactivity of both T and B lymphocytes which may be in response to HIV antigens themselves, and the second is a loss in T-cell activity in response to other antigens. Dendritic cells (DC) show a higher rate of infection with HIV than other peripheral blood cells in vitro and in vivo. The effects of HIV infection of DC in vitro on their stimulating capacity for T cells were, therefore, examined. We compared the development of the capacity to stimulate primary proliferative responses to virus in autologous lymphocytes with their potency in stimulating allogeneic cells in the mixed leukocyte reaction (MLR). Small numbers of uninfected DC caused little or no stimulation of autologous lymphocytes, but stimulated high MLR. The level of HIV infection in in vitro infected DC preparations was dependent on the time of infection and the titre of the input virus. DC exposed to low doses of HIV (e.g., 10(3) TCID/10(6) cells) for up to 4 days or to a higher dose (e.g. 10(5) TCID/10(6) cells) for 1 day caused significant primary proliferation in autologous T cells and, under these conditions, capacity to stimulate allogeneic MLR remained intact. However, DC exposed to increasing doses of HIV or infected for a longer period showed reduced capacity to stimulate allogeneic lymphocytes and then a loss of stimulation of autologous cells. This provides evidence suggesting that both stimulatory and inhibitory effects of HIV infection can be produced through infection of DC.

Development and function of dendritic cells in health and disease

The life history of dendritic cells (DC) is now established from their origins from bone marrow stem cells, their distribution through blood to the tissues, and their movement via afferent lymph to lymph nodes for the initiation of immune responses. Bone-marrow stem cells, and occasional stem cells in peripheral blood (about 1 per 10(5) mononuclear cells), can give rise both to DC and macrophages (MO). In addition to stem cells in blood, after short-term culture of mononuclear cells, three major morphologic types of DC can be separated (types I-III), which probably represent the maturational pathway of this cell type; type II cells resemble tissue DC such as Langerhans cells and type III have a veiled morphology similar to that seen in cells of afferent lymph and in the interdigitating cells of the paracortex of lymph nodes. Functionally, DC cultured from peripheral blood are able to acquire large antigens and process them like Langerhans cells of the skin. They can also present antigens to stimulate primary T-cell responses, a property associated with lymph node DC. In tissues, DC appear to act as outposts of the immune system, acquire antigens, and, particularly in primary responses, carry the antigens to lymph nodes where they initiate T-cell responses. In secondary responses, activation of memory T cells in the periphery and the acquisition of antigen/antibody complexes by follicular dendritic cells of the lymph node follicles, which stimulate B cell memory, may be more important pathways for immune activation. DC may play a role in the development of many immunologic diseases including cancer, autoimmunity, and acquired immunodeficiency syndrome (AIDS).

Dendritic cells from patients with tropical spastic paraparesis are infected with HTLV-1 and stimulate autologous lymphocyte proliferation

Dendritic cells (DC), important antigen-presenting cells for recruiting T cells into immune responses, are susceptible to infection with HIV-1 and this can cause either stimulatory or suppressive effects on T cells. We examined another human retrovirus, HTLV-1, to determine whether DC were infected and caused any changes in T-cell function. Patients infected with HTLV-1 who have tropical spastic paraparesis (TSP) show high 'spontaneous' lymphocyte proliferation. We studied the basis for this by analyzing the interactions in vitro between lymphocytes and antigen-presenting cells and compared cells taken from HTLV-1-positive TSP patients with those taken from HTLV-1-positive healthy carriers and HTLV-1-negative family members. In HTLV-1-positive individuals, 0.4-5.1% of the DC were infected with HTLV-1 as determined by in situ hybridisation. In TSP patients, depletion of DC and purification of T cells abolished 'spontaneous' lymphocyte proliferation. Reinstating the DC, but not B cells or macrophages, restored proliferation, an effect that was blocked by antibodies either to class II major histocompatibility antigens or to HTLV-1 itself. Thus, presentation of HTLV-1 antigens by infected DC to autologous T cells could result in the abnormal T-cell proliferation and cause the inflammatory reaction leading to tissue damage in TSP. We also speculate that persistent infection of DC with HTLV-1 and consequent continuous stimulation of T cells might be instrumental in the development of HTLV-1-mediated T-cell leukemia.

Neuronal protein NP185 is developmentally regulated, initially expressed during synaptogenesis, and localized in synaptic terminals

Evidence is presented here that demonstrates the presence of NP185 (AP3) in neuronal cells, specifically within syn-aptic terminals of the central nervous system and in the peripheral nervous system, particularly in the neuro-muscular junction of adult chicken muscle. Biochemical results obtained in our laboratories indicate that NP185 is associated with brain synaptic vesicles, with clathrin-coated vesicles, and with the synaptosomal plasma membrane. Also, NP185 binds to tubulin and clathrin light chains and the binding is regulated by phosphorylation (Su et al., 1991). Based on these properties and the data reported here, we advance the postulate that NP185 fulfills multiple functions in synaptic terminals. One function is that of a plasma membrane docking or channel protein, another of a signaling molecule for brain vesicles to reach the synaptic terminal region, and a third is that of a recycling molecule by binding to protein components on the lipid bilayer of the synaptic plasma membrane during the process of endocytosis. In support of these premises, a thorough study of NP185 using the developing chick brain, adult mouse brain, and chicken straited muscle was begun by temporally and spatially mapping the expression and localization of NP185 in evolving and mature nerve endings. To achieve these objectives, monoclonal antibodies to NP185 were used for immunocytochemistry in tissue sections of chicken and mouse cerebella. The distribution of NP185 was compared with those of other cytoskeletal and cytoplasmic proteins of axons and synapses, namely synaptophysin, vimentin, neurofilament NF68, and the intermediate filaments of glial cells (GFAP). The data indicate that expression of NP185 temporally coincides with synaptogenesis, and that the distribution of this protein is specific for synaptic terminal buttons of the CNS and the PNS.

Ovine lentivirus is macrophagetropic and does not replicate productively in T lymphocytes

The lentiviruses of sheep, goats, and horses cause chronic multiorgan disease in which macrophages are highly permissive for viral replication. Monocytes, which mature into macrophages, are thought to be latently infected with lentivirus, but the extent to which other leukocytes are infected is unknown. Dendritic cells have not been studied separately from monocytes and T-cell subsets have not been examined in previous attempts to identify infected cells in peripheral blood mononuclear cells (PBMC). We found no evidence of T-cell tropism using an animal-passaged, pathogenic ovine lentivirus. Phytohemagglutinin-stimulated infectious PBMC produced 20-fold less virus than differentiated macrophages, and cocultivation of infectious PBMC with fresh, uninfected phytohemagglutinin blasts did not facilitate virus replication. Furthermore, central lymph cells, the best in vivo source of purified lymphocytes, lacked virus and did not yield virus upon in vitro cultivation. In contrast, cultivated blood-derived macrophages were highly permissive for viral replication. To identify the latently infected PBMC, PBMC from infected sheep were selectively depleted of monocytes and B cells by passage over nylon wool and then of nonadherent cells bearing CD4, CD8, T19, gamma delta T-cell receptor, CD45RA, or major histocompatibility complex class II antigens by panning. Removal of adherent monocytes and B cells or of adherent cells and the three major T-cell subsets (CD4+, CD8+, T19+) did not decrease the infectivity of PBMC. The richest sources of infected cells in fresh PBMC were CD45RA+ and major histocompatibility complex class II+ nonadherent cells, which are three characteristics of dendritic cells. Thus, the dendritic cell, and not the monocyte or the CD4+ cell, is probably the predominant infected cell type in blood.

Apparent fusion of basement membranes in colorectal carcinoma

Previous studies on colorectal carcinomas indicate that consistent differences in epithelial basement membrane (EBM) integrity are present between the tumour centre and periphery. We report that within the tumour centre, EBM staining between back-to-back (BTB) neoplastic glands (i.e., adjacent glands in direct contact with no intervening connective tissue) generally follows a pattern different from that of EBM staining at the tumour:stromal interface (TSI). Such distinctions are important, since the factors responsible for EBM deficiencies may vary with intra-tumoural location, as may the prognostic significance of these deficiencies. Analysis of paraffin sections from 130 colorectal carcinoma cases showed that EBM staining between BTB glands is generally weaker and more discontinuous than at the TSI, sometimes appearing as a linear array of immunostained granules on high-resolution light microscopy. By double-labelling immunofluorescence analysis of cryostat sections from 30 cases, a decrease in type-IV collagen:laminin staining intensity ratio was found between BTB glands. Hence, the composition of EBM between BTB glands appears to be abnormal. As much recent evidence indicates that epithelial:mesenchymal interactions play an essential role in EBM formation, the demonstration of immunostained EBM fragments between BTB glands requires an explanation: We suggest that the synthesis of EBM between BTB glands involved previously intervening stromal (mesenchymal) cells, and that EBM fusion and dissolution occur between BTB glands following the displacement of these cells.