The neural inductive response of competent chick ectoblast decreases away from the host axis and correlates with an increased proliferative activity.

We have assessed the quality and quantity of the neural inductive response of the chick gastrula ectoblast located at increasing distancefrom the host axis. In a stage 4 gastrula, entire ectoblast exhibits neural competence. The quality of induced neural tissue shifts from deuterencephalic type in the area pellucida to archencephalic type in the area opaca and primitive medullary or palisade type atthe margin of overgrowth with a concomitant reduction in the number of induced neural cells. In contrast, the mitotic and 3H-TdR labelling frequencies in the competent ectoblast increase with increasing distance from the host axis and in a proportion inverse to the amount of induced neural tissue. It is suggested that the strong neural inductive response is correlated with low proliferative activity, or longer cell cycle time, of the competent ectoblast.     

The neural inductive signal is transferred to ectoblast in 1-2 h but a continued contact with mesoblast for 2-3 h is essential for neuralization in the chick area pellucida.

In the area pellucida of the chick gastrula, the Hensen's node (HN) graft must contact the competent ectoblast for at least 4 h to promote neural induction. When we removed the grafted HN after 1 to 3 h and replaced it by a non-inducing post nodal (PN) fragment, a 1-2 h contact with HN was found to be sufficient to promote neural induction. When HN graft was removed after 3 or 4 h and replaced by PN, the neural inductive response was substantially improved towards formation of archencephalic structures. Thus, our results indicate that neural induction takes place in two steps. In the first step, a contact with HN for 1-2 h is sufficient to transferthe inductive signal which is stabilized through a second step involving continued cell-cell contact with even non-inducing PN mesoblast.     

Post-nodal mesoblast caudalizes the host axis and inhibits cell population growth, and induces new primitive streaks in chick embryos

One to eight post-nodal fragments (PN) or Hensen's nodes (HN) from full primitive streak stage chick embryos were transplanted onto the area pellucida or area opaca of stage 4 embryos and cultured for 20 h. Thirteen morphological and numerical parameters were affected in the host embryos and analyzed by multiple logistic regression for parametric hierarchy. In the area pellucida, both PN and HN transplants inhibited cell population growth while only PN caudalized the host axis and induced supernumerary primitive streaks expressing the mesoderm-specific gene Brachyury. In the area opaca, neither grafts influenced host axis morphogenesis, but PN inhibited the cell population growth significantly. Tracking [(3)H]TdR labeled grafts showed that PN cells migrated towards the host axis and participated in the formation of supernumerary somites and hearts. When placed near the host axis, PN caudalized it and inhibited cell population growth.     

Cx37 and Cx43 localize to zona pellucida in mouse ovarian follicles

In the ovarian follicle, granulosa cells adjacent to the oocyte extend processes through the zona pellucida matrix, and these projections establish gap junctions both with the oocyte and with neighboring transzonal projections. The identity of connexins contributing to gap junctions between transzonal projections has not been extensively studied. Here, we examined the expression pattern of Cx37 and Cx43 in mouse zona pellucida using multiple connexin-specific antibodies. Immunofluorescence staining revealed abundant Cx37 and Cx43 puncta within the zona pellucida of both preantral and antral follicles. Cx37 persisted in the zona pellucida of mature follicles up to 5 h after an ovulatory stimulus whereas Cx43 was reduced in the zona pellucida by 3 h after an ovulatory stimulus. We suggest that in addition to its role in oocyte-granulosa cell communication, Cx37 could enable a distinct communication pathway between those granulosa cells that are in direct contact with the oocyte.     

Cx37 and Cx43 Localize to Zona Pellucida in Mouse Ovarian Follicles

In the ovarian follicle, granulosa cells adjacent to the oocyte extend processes through the zona pellucida matrix, and these projections establish gap junctions both with the oocyte and with neighboring transzonal projections. The identity of connexins contributing to gap junctions between transzonal projections has not been extensively studied. Here, we examined the expression pattern of Cx37 and Cx43 in mouse zona pellucida using multiple connexin-specific antibodies. Immunofluorescence staining revealed abundant Cx37 and Cx43 puncta within the zona pellucida of both preantral and antral follicles. Cx37 persisted in the zona pellucida of mature follicles up to 5 h after an ovulatory stimulus whereas Cx43 was reduced in the zona pellucida by 3 h after an ovulatory stimulus. We suggest that in addition to its role in oocyte-granulosa cell communication, Cx37 could enable a distinct communication pathway between those granulosa cells that are in direct contact with the oocyte.     

Co-Expression of Cytokeratins and Vimentin in Sheep Cumulus-Oocyte Complexes. Alteration of Intermediate Filament Distribution by Acrylamide

The association between germ cells and somatic granulosa cells persists throughout the growth of the oocyte by means of foot processes of the cumulus corona cells that cross the zona pellucida. During meiotic maturation important nuclear and cytoplasmic events occur in cumulus-oocyte complex suggesting implication of cytoskeletal elements. Immunoblotting analysis of cytoskeletal proteins of the cumulus cells revealed the presence of vimentin polypeptide and of at least two cytokeratin polypeptides. Using immunofluorescence techniques on cryostat sections through frozen tissue, we provided evidence for the presence of cytokeratins of the simple epithelial type in addition to vimentin in sheep cumulus cells. These two types of intermediate filaments were localized throughout the cytoplasm and especially in the foot processes which cross the zona pellucida. The contact area between the two cell types was also labelled with the antibodies. Acrylamide treatment of cumulus-oocyte complexes involved a drastic disorganization of the intermediate filament network and triggered the isolation of the oocyte from its cumulus cells. This isolation resulted in resumption of meiosis. From these results it appears that intermediate filaments could participate in the process of gap junction loss and indirectly in the control of meiosis resumption.     

Species- and clone-specific responses to environmental stimuli in the cladocerans Bosmina cornuta and B. pellucida - a comparison with Daphnia

We studied the variation of small-scale swimming behaviour in eight Bosmina cornuta and ten B. pellucida clones in response to key environmental factors to test whether swimming behaviour and genotypes are linked in non-Daphnia cladocerans. We quantified (1) the short-term responses to changes in temperature, light intensity and pH, (2) the response to long-term temperature acclimation, and (3) the pH-related survival rates. Vertical swimming activity S was quantified in cuvette experiments as crossings of a line at 2 cm height per individual an hour. S differed significantly among species and conspecific clones. At any temperature, light intensity and pH tested, B. cornuta (clone variation: 40-58 crossings/ind.- h) showed a higher vertical swimming activity than B. pellucida (clone variation: 25-48 crossings/ind.- h). A short-term change of water temperature (range tested: 10-25C) only affected S of B. cornuta, whereas that of B. pellucida remained unaltered. In contrast, S increased with rising temperature following long-term temperature acclimation (range tested: 10-20C) in both species. Swimming activity was inversely related to the light intensity (range tested: 60-60,000 lux), but decrease of activity was stronger in B. pellucida (44′ 12 crossings/ind - h) than in B. cornuta (50′ 40 crossings/ind.- h). Short-term changes of pH (range tested: 4-6) did not influence swimming activity in any species, although a prolonged exposure (24 h) to pH 4 was lethal. Thus, Bosmina showed behavioural responses which permit to distinguish between the species and which are related to their seasonal succession and distribution pattern.     

Effects of exposure of epididymal boar spermatozoa to seminal plasma on the binding of zona pellucida proteins during in vitro capacitation

The purpose of the investigation was to determine whether seminal plasma plays a role in the increase during in vitro capacitation of the number of boar spermatozoa with enhanced binding of zona pellucida proteins. Ejaculated spermatozoa and spermatozoa collected from the caudae epididymides of boars were incubated at 39 degrees C in a Tyrode's IVF medium. During incubation, the zona binding ability of individual spermatozoa was assessed with fluorescein-conjugated solubilized zona pellucida proteins (FITC-sZP), using a flow cytometer. Propidium iodide (PI) was included to simultaneously monitor cell viability. During incubation of ejaculated spermatozoa, a percentage of the spermatozoa expressed enhanced binding of FITC-sZP. The percentage of viable spermatozoa with enhanced binding reached a maximum of 37% (S.D.=8, averaged over five boars) after 2-3 h. In epididymal sperm, a similar maximum was observed after incubation in vitro, but a longer time of incubation was needed (6 h). Also, the rate of cell death of epididymal sperm was much lower than that of ejaculated sperm. When epididymal spermatozoa was exposed to seminal plasma in vitro, the time needed to reach a maximal percentage of viable spermatozoa with enhanced FITC-sZP binding was similar to that in ejaculated semen. However, the rate of cell death was still much lower than in ejaculated sperm. We concluded that the binding sites on the sperm surface that are involved in the increased binding of zona proteins during incubation under IVF conditions were not derived from the seminal plasma. The cellular processes leading to the increased binding capacity were accelerated by exposure of the sperm to seminal plasma.     

Race-Specific Elicitors of Cladosporium fulvum Induce Changes in Cell Morphology and the Synthesis of Ethylene and Salicylic Acid in Tomato Plants Carrying the Corresponding Cf Disease Resistance Gene

Defense responses mediated by the genetically unlinked Cf-9 and Cf-2 genes were compared with those involving no Cf gene (Cf0). Compatible tomato (Lycopersicon esculentum)-Cladosporium fulvum intercellular washing fluids were injected into tomato cotyledons, and the kinetics of responses was monitored under conditions of 70 and 98% relative humidity. The latter conditions suppressed the normal macroscopic responses. For the Cf-9-Avr9 interaction, stomatal opening was induced within 3 to 4 h and after 9 h mesophyll cell death commenced. A burst of ethylene production occurred between 9 and 12.5 h and remained elevated. Free salicylic acid levels increased after 12 h, peaked at 24 h, and thereafter declined. For the Cf-2-Avr2 interaction, stomata became plugged after 8 h, and salicylic acid and ethylene levels increased by 12 and 18 h, respectively, and thereafter declined. Host cell death commenced around vascular tissue by 24 h. Cell death in both incompatible interactions was frequently preceded by cell enlargement. For Cf0-injected plants, no significant responses were detected. High humidity delayed and reduced the Cf-Avr-gene-dependent cell death and ethylene synthesis, whereas induced salicylic acid levels were unaffected for Cf-2-Avr2 and reduced in magnitude only for Cf-9-Avr9.     

Engineering systems for the generation of patterned co-cultures for controlling cell–cell interactions

Background

Inside the body, cells lie in direct contact or in close proximity to other cell types in a tightly controlled architecture that often regulates the resulting tissue function. Therefore, tissue engineering constructs that aim to reproduce the architecture and the geometry of tissues will benefit from methods of controlling cell–cell interactions with microscale resolution.

Scope of the review

We discuss the use of microfabrication technologies for generating patterned co-cultures. In addition, we categorize patterned co-culture systems by cell type and discuss the implications of regulating cell–cell interactions in the resulting biological function of the tissues.

Major conclusions

Patterned co-cultures are a useful tool for fabricating tissue engineered constructs and for studying cell–cell interactions in vitro, because they can be used to control the degree of homotypic and heterotypic cell–cell contact. In addition, this approach can be manipulated to elucidate important factors involved in cell–matrix interactions.

General significance

Patterned co-culture strategies hold significant potential to develop biomimetic structures for tissue engineering. It is expected that they would create opportunities to develop artificial tissues in the future.This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.     

Analysis of CD4 gene expression in human fetal brain and neuroblasts

1. The expression of the gene codifying for CD4, the most important human immunodeficiency virus type 1 (HIV-1) receptor molecule, was analyzed in 11 fetal brains at various gestational ages and in 9 human neuroblastoma (NB) cell lines. CD4 gene expression in fetal and malignant neural cells was then compared with that observed in a hematopoietic cell line and adult hippocampus. 2. In addition, CD4 mRNA was evaluated in two NB cell lines induced to differentiate in vitro with retinoic acid (RA) or 1-(5-isoquinolinyl-sulfonyl)-2-methyl piperazine (H7), a protein kinase C inhibitor. 3. All fetal brains and NB cell lines express a 1.8-kb signal when hybridized with pT4BcDNA probe, while a 3.0-kb signal such as observed in hematopoietic human cells was found in 1 of 11 fetal brains and in 0 of 9 NB cell lines. The 1.8-kb signal was lost in all analyzed poly(A)+ mRNA samples. 4. Moreover, CD4 gene expression was not induced in either RA- or H7-treated NB cells at any tested time and dose. The analysis of NB cells by polymerase chain reaction failed to demonstrate CD4 expression in either poly(A)+ or poly(A)- RNA. 5. In conclusion, the results show that the 1.8-kb signal observed in RNA extracted from fetal or transformed human neural cells is probably due to an aspecific hybridization. However, the gene codifying for CD4 can rarely be expressed by fetal brain cells early during gestation, in still unclear circumstances.     

Embryonic induction and cation concentrations in amphibian embryos

Explanted ectoderm from early gastrulae of Triturus alpestris was treated with the Na-K ionophore gramicidin (10(-9) to 10(-5) M) and the Ca-ionophore A 23187 (10(-7) to 10(-5) M). The ectoderm developed almost exclusively to atypical epidermis as in the control explants. When the ectoderm was treated with ouabain (10(-4) M), intracellular Na+ increased about 4.4-fold and K+ was reduced by half. Mesenchyme cells in small number differentiated in about 40% of the ouabain-treated explants. The time course of total Na+ and K+ ion concentrations was measured over a period of 72 h in ectoderm of T. alpestris after induction with vegetalizing factor and in control explants. In the first 15 h after explantation, no significant differences between control and induced explants were found. Thereafter, the steady state concentration of K+ decreased in the induced explants, whereas the steady-state concentration of Na+ slightly increased. The membrane resting potential recorded intracellularly of ectoderm sandwiches from early gastrula stages was found to be -41.3 mV in control and -59.3 mV in induced explants. From the specific conductances and permeabilities of non-induced and induced cells it is concluded that the induction process leads to a differentiation of the cell membrane, which acquires the characteristics of ionic selectivity. Ectoderm from Ambystoma mexicanum forms neural or neuroid tissue, mesenchyme and melanophores after explantation in salt solution in up to 50% of the explants without any additions. Isolated Ambystoma ectoderm is therefore not suitable for test experiments.     

Human mast cells release metalloproteinase-9 on contact with activated T cells: juxtacrine regulation by TNF-alpha

Mast cells, essential effector cells in allergic inflammation, have been found to be activated in T cell-mediated inflammatory processes in accordance with their residence in close physical proximity to T cells. We have recently reported that mast cells release granule-associated mediators and TNF-alpha upon direct contact with activated T cells. This data suggested an unrecognized activation pathway, where mast cells may be activated during T cell-mediated inflammation. Herein, we show that this cell-cell contact results in the release of matrix metalloproteinase (MMP)-9 and the MMP inhibitor tissue inhibitor of metalloproteinase 1 from HMC-1 human mast cells or from mature peripheral blood-derived human mast cells. The expression and release of these mediators, as well as of beta-hexosaminidase and several cytokines, were also induced when mast cells were incubated with cell membranes isolated from activated, but not resting, T cells. Subcellular fractionation revealed that the mature form of MMP-9 cofractionated with histamine and tryptase, indicating its localization within the secretory granules. MMP-9 release was first detected at 6 h and peaked at 22 h of incubation with activated T cell membranes, while TNF-alpha release peaked after only 6 h. Anti-TNF-alpha mAb inhibited the T cell membrane-induced MMP-9 release, indicating a possible autocrine regulation of MMP release by mast cell TNF-alpha. This cascade of events, whereby mast cells are activated by T cells to release cytokines and MMP-9, which are known to be essential for leukocyte extravasation and recruitment to affected sites, points to an important immunoregulatory function of mast cells within the context of T cell-mediated inflammatory processes.     

Expression of membrane type-4 matrix metalloproteinase (metalloproteinase-17) by human eosinophils

Circulating eosinophils need proteinases to mediate a spatially limited and orientated digestion of the extracellular matrix and to migrate into tissue. Moreover, proteinases are likely involved in tissue remodeling, a crucial feature of chronic diseases including asthma. Eosinophils express matrix metalloproteinase (MMP)-9, which is increased upon stimulation with TNF-. Other MMPs, the membrane type (MT)-MMPs, likely play a major role in cell invasion and tissue remodeling. MT4-MMP was identified in peripheral blood leukocyte preparations, but it is not known whether eosinophils express MT4-MMP. We investigated the expression of MT4-MMP and its modulation by TNF- in purified human blood eosinophils. The constitutive expression of MT4-MMP mRNA was detected by RT-PCR in unstimulated eosinophils, lymphocytes, and monocytes, but not neutrophils. Stimulation of eosinophils with TNF- increased MT4-MMP mRNA expression. This effect appeared at 4 h and reached a maximum at 8 h of incubation. MT4-MMP protein was detected in freshly isolated blood eosinophils by Western blotting and immunocytochemistry. TNF- increased expression of the MT4-MMP protein. MT4-MMP protein was also detected in nasal polyp eosinophils by immunohistochemistry. In conclusion, eosinophils constitutively express MT4-MMP, which is increased upon stimulation with TNF-. Consequently, MT4-MMP may be directly involved in the degradation of extracellular matrix components and/or modulate the activity of other proteins implicated in eosinophil migration and tissue remodeling.     

Zona pellucida protein binding ability of porcine sperm during epididymal maturation and the acrosome reaction

In many mammals, the first interaction between gametes during fertilization occurs when sperm contact the zona pellucida surrounding the egg. Although porcine sperm first contact the zona pellucida via their plasma membrane, the regions of the sperm surface that display zona receptors have not been determined. We have used the Alexa 488 fluorophore conjugated to solubilized porcine zona pellucida proteins to observe zona receptors on live boar sperm. Zona proteins bound live, acrosome-intact sperm on the anterior portion of the sperm head, concentrated in a thin band over the acrosomal ridge. When sperm membranes were permeabilized by fixation or acrosome reactions induced by the ionophore A23187, zona binding was extended to a broad area covering the entire acrosomal region. Zona binding proteins were present in the acrosomes of sperm from all regions of the epididymis. In contrast, zona binding sites were found on the plasma membrane of most sperm from the corpus and cauda epididymis, but on only 6% of caput epididymal sperm. In conclusion, acrosome-intact boar sperm exhibit concentrated zona protein binding over the acrosomal ridge and acquire this binding in the corpus region of the epididymis, correlating with the developmental stage at which sperm gain the ability to fertilize oocytes.     

Effect of specific phosphodiesterase isoenzyme inhibitors during in vitro maturation of bovine oocytes on meiotic and developmental capacity

Compared with oocytes matured in vivo, in vitro-matured oocytes are compromised in their capacity to support early embryo development. Delaying spontaneous in vitro meiotic maturation using specific phosphodiesterase (PDE) isoenzyme inhibitors may permit more complete oocyte cytoplasmic maturation, possibly by prolonging cumulus cell (CC)-oocyte gap junctional communication during meiotic resumption. This study aimed to investigate the effect of the isoenzyme 3- (oocyte) and isoenzyme 4- (granulosa cell) specific PDE inhibitors on the kinetics of in vitro maturation and on subsequent oocyte developmental competence. Cumulus-oocyte complexes from antral bovine follicles were isolated and cultured in the presence of the specific PDE inhibitors milrinone (type 3) or rolipram (type 4) (100 microM). In the presence of FSH, both PDE inhibitors only slightly extended CC-oocyte gap junctional communication over the first 9 h, but they completely blocked meiotic resumption during this period (P < 0.001). The indefinite inhibitory effect of milrinone on meiotic resumption (30% at germinal vesicle stage after 48 h) was overridden by 24 h when treated with FSH, but not with hCG, suggesting a form of induced meiotic resumption. Oocytes treated with FSH with or without either PDE inhibitor were inseminated at either 24, 26, or 28 h. Treated with either the type 3 or type 4 PDE inhibitor significantly (P < 0.05) increased embryo development to the blastocyst stage by 33%-39% (to an average of 52% blastocysts) compared with control oocytes (38%) after insemination at 28 h, and significantly (P < 0.05) increased blastocyst cell numbers when inseminated at 24 h. These results suggest that delayed spontaneous meiotic maturation, coupled with extended gap junctional communication between the CCs and the oocyte has a positive effect on oocyte cytoplasmic maturation, thereby improving oocyte developmental potential.     

All-trans retinoic acid induces apoptosis in acute myeloblastic leukaemia cells

The effect of all-trans retinoic acid (ATRA) on leukaemia cell differentiation, proliferation and induction of apoptosis was studied by using autonomously growing blast cells isolated from eight patients with acute myeloblastic leukaemia (AML) either at diagnosis ( n=4) or at relapse (n=4). No morphological or functional differentiation induced by ATRA was observed in any of the cases studied. In cell cultures, inhibition of leukaemia cell growth by ATRA was obvious, especially in the case of clonogenic cells, and it was both time- and concentration-dependent. Induction of apoptosis was more difficult to achieve. The cells retained over 90% viability in suspension when the ATRA exposure at any of the concentrations studied was 48 h or less. When the time of exposure to ATRA was longer than 48 h, the viability of the cells decreased in a concentration-dependent manner. Apoptosis was observed morphologically in each of the AML cases with 10-5 to 10-8 M ATRA, if the incubation time of cells in ATRA was 72 h. The percentage of apoptotic cells increased with increasing ATRA concentrations from 12± 9% of 10-8 M ATRA to 78±12% of 10-5 M ATRA. The DNA electrophoretic method was able to detect apoptosis in all the AML samples exposed to 10-7 and 10-6 ATRA for 48 h and occasionally in cases where lower concentrations and longer exposure time were used. In conclusion, the present study shows that it is possible to induce apoptotic leukaemia cell death in vitro with ATRA in AML, and this effect is dependent on both concentration and exposure time.     

Shear stress induces preimplantation embryo death that is delayed by the zona pellucida and associated with stress-activated protein kinase-mediated apoptosis

In this study, we discovered that embryos sense shear stress and sought to characterize the kinetics and the enzymatic mechanisms underlying induction of embryonic lethality by shear stress. Using a rotating wall vessel programmed to produce 1.2 dynes/cm2 shear stress, it was found that shear stress caused lethality within 12 h for E3.5 blastocysts. Embryos developed an approximate 100% increase in mitogen-activated protein kinase 8/9 (formerly known as stress-activated protein kinase/junC kinase 1/2) phosphorylation by 6 h of shear stress that further increased to approximately 350% by 12 h. Terminal deoxynucleotidyltransferase dUTP nick end labeling/apoptosis was at baseline levels at 6 h and increased to approximately 500% of baseline at 12 h, when irreversible commitment to death occurred. A mitogen-activated protein kinase 8/9 phosphorylation inhibitor, D-JNKI1, was able to inhibit over 50% of the apoptosis, suggesting a causal role for mitogen-activated protein kinase 8/9 phosphorylation in the shear stress-induced lethality. The E2.5 (compacted eight-cell/early morula stage) embryo was more sensitive to shear stress than the E3.5 (early blastocyst stage) embryo. Additionally, zona pellucida removal significantly accelerated shear stress-induced lethality while having no lethal effect on embryos in the static control. In conclusion, preimplantation embryos sense shear stress, chronic shear stress is lethal, and the zona pellucida lessens the lethal and sublethal effects of shear stress. Embryos in vivo would not experience as high a sustained velocity or shear stress as induced experimentally here. Lower shear stresses might induce sufficient mitogen-activated protein kinase 8/9 phosphorylation that would slow growth or cause premature differentiation if the zona pellucida were not intact.     

T lymphocytes activated by persistent viral infection differentially modify the expression of metalloproteinases and their endogenous inhibitors, TIMPs, in human astrocytes: relevance to HTLV-I-induced neurological disease

Activation of T lymphocytes by human pathogens is a key step in the development of immune-mediated neurologic diseases. Because of their ability to invade the CNS and their increased secretion of proinflammatory cytokines, activated CD4+ T cells are thought to play a crucial role in pathogenesis. In the present study, we examined the expression of inflammatory mediators the cytokine-induced metalloproteinases (MMP-2, -3, and -9) and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMP-1, -2, and -3), in human astrocytes in response to activated T cells. We used a model system of CD4+ T lymphocytes activated by persistent viral infection (human T lymphotropic virus, HTLV-I) in transient contact with human astrocytes. Interaction with T cells resulted in increased production of MMP-3 and active MMP-9 in astrocytes despite increased expression of endogenous inhibitors, TIMP-1 and TIMP-3. These data suggest perturbation of the MMP/TIMP balance. These changes in MMP and TIMP expression were mediated, in part, by soluble factors (presumably cytokines) secreted by activated T cells. Integrin-mediated cell adhesion is also involved in the change in MMP level, since blockade of integrin subunits (alpha1, alpha3, alpha5, and beta1) on T cells resulted in less astrocytic MMP-9-induced expression. Interestingly, in CNS tissues from neurological HTLV-I-infected patients, MMP-9 was detected in neural cells within the perivascular space, which is infiltrated by mononuclear cells. Altogether, these data emphasize the importance of the MMP-TIMP axis in the complex interaction between the CNS and invading immune cells in the context of virally mediated T cell activation.