Localization of microglia in the human fetal cervical spinal cord

Developmental Associations between Neurovascularization and Microglia Colonization

The temporal and spatial pattern of microglia colonization and vascular infiltration of the nervous system implies critical associated roles in early stages of nervous system development. Adding to existing reviews that cover a broad spectrum of the various roles of microglia during brain development, the current review will focus on the developmental ontogeny and interdependency between the colonization of the nervous system with yolk sac derived macrophages and vascularization. Gaining a better understanding of the timing and the interdependency of these two processes will significantly contribute to the interpretation of data generated regarding alterations in either process during early development. Additionally, such knowledge should provide a framework for understanding the influence of the early gestational environmental and the impact of genetics, disease, disorders, or exposures on the early developing nervous system and the potential for long-term and life-time effects.

Microglia Colonization Associated with Angiogenesis and Neural Cell Development

The temporal and spatial pattern of microglia colonization of the nervous system implies a role in early stages of organ development including cell proliferation, differentiation, and neurovascularization. As microglia colonize and establish within the developing nervous system, they assume a neural-specific identity and contribute to key developmental events. Their association around blood vessels implicates them in development of the vascular system or vice versa. A similar association has been reported for neural cell proliferation and associated phenotypic shifts and for cell fate differentiation to neuronal or glial phenotypes. These processes are accomplished by phagocytic activities, cell-cell contact relationships, and secretion of various factors. This chapter will present data currently available from studies evaluating the dynamic and interactive nature of these processes throughout the progression of nervous system development.

Microglial regional heterogeneity and its role in the brain

Microglia have been recently shown to manifest a very interesting phenotypical heterogeneity across different regions in the mammalian central nervous system (CNS). However, the underlying mechanism and functional meaning of this phenomenon are currently unclear. Baseline diversities of adult microglia in their cell number, cellular and subcellular structures, molecular signature as well as relevant functions have been discovered. But recent transcriptomic studies using bulk RNAseq and single-cell RNAseq have produced conflicting results on region-specific signatures of microglia. It is highly speculative whether such spatial heterogeneity contributes to varying sensitivities of individual microglia to the same physiological and pathological signals in different CNS regions, and hence underlie their functional relevance for CNS disease development. This review aims to thoroughly summarize up-to-date knowledge on this specific topic and provide some insights on the potential underlying mechanisms, starting from microgliogenesis. Understanding regional heterogeneity of microglia in the context of their diverse neighboring neurons and other glia may provide an important clue for future development of innovative therapies for neuropsychiatric disorders.

Differences of Microglia in the Brain and the Spinal Cord

Microglia were previously regarded as a homogenous myeloid cell lineage in the mammalian central nervous system (CNS). However, accumulating evidences show that microglia in the brain and SC are quite different in development, cellular phenotypes and biological functions. Although this is a very interesting phenomenon, the underlying mechanisms and its significance for neurological diseases in association with behavioral and cognitive changes are still unclear. How microglia differ between these two regions and whether such diversity may contribute to CNS development and functions as well as neurological diseases will be discussed in this Perspective.

Microglial Dynamics During Human Brain Development

Microglial cells are thought to colonize the human cerebrum between the 4th and 24th gestational weeks. Rodent studies have demonstrated that these cells originate from yolk sac progenitors though it is not clear whether this directly pertains to human development. Our understanding of microglial cell dynamics in the developing human brain comes mostly from postmortem studies demonstrating that the beginning of microglial colonization precedes the appearance of the vasculature, the blood–brain barrier, astrogliogenesis, oligodendrogenesis, neurogenesis, migration, and myelination of the various brain areas. Furthermore, migrating microglial populations cluster by morphology and express differential markers within the developing brain and according to developmental age. With the advent of novel technologies such as RNA-sequencing in fresh human tissue, we are beginning to identify the molecular features of the adult microglial signature. However, this is may not extend to the much more dynamic and rapidly changing antenatal microglial population and this is further complicated by the scarcity of tissue resources. In this brief review, we first describe the various historic schools of thought that had debated the origin of microglial cells while examining the evidence supporting the various theories. We then proceed to examine the evidence we have accumulated on microglial dynamics in the developing human brain, present evidence from rodent studies on the functional role of microglia during development and finally identify limitations for the used approaches in human studies and highlight under investigated questions.

Markers of microglia in post-mortem brain samples from patients with Alzheimer's disease: a systematic review

Neuroinflammation is proposed as one of the mechanisms by which Alzheimer's disease pathology, including amyloid-β plaques, leads to neuronal death and dysfunction. Increases in the expression of markers of microglia, the main neuroinmmune cell, are widely reported in brains from patients with Alzheimer's disease, but the literature has not yet been systematically reviewed to determine whether this is a consistent pathological feature. A systematic search was conducted in Medline, Embase and PsychINFO for articles published up to 23 February 2017. Papers were included if they quantitatively compared microglia markers in post-mortem brain samples from patients with Alzheimer's disease and aged controls without neurological disease. A total of 113 relevant articles were identified. Consistent increases in markers related to activation, such as major histocompatibility complex II (36/43 studies) and cluster of differentiation 68 (17/21 studies), were identified relative to nonneurological aged controls, whereas other common markers that stain both resting and activated microglia, such as ionized calcium-binding adaptor molecule 1 (10/20 studies) and cluster of differentiation 11b (2/5 studies), were not consistently elevated. Studies of ionized calcium-binding adaptor molecule 1 that used cell counts almost uniformly identified no difference relative to control, indicating that increases in activation occurred without an expansion of the total number of microglia. White matter and cerebellum appeared to be more resistant to these increases than other brain regions. Nine studies were identified that included high pathology controls, patients who remained free of dementia despite Alzheimer's disease pathology. The majority (5/9) of these studies reported higher levels of microglial markers in Alzheimer's disease relative to controls, suggesting that these increases are not solely a consequence of Alzheimer's disease pathology. These results show that increased markers of microglia are a consistent feature of Alzheimer's disease, though this seems to be driven primarily by increases in activation-associated markers, as opposed to markers of all microglia.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

Inflammation in utero exacerbates ventilation-induced brain injury in preterm lambs

Cerebral blood flow disturbance is a major contributor to brain injury in the preterm infant. The initiation of ventilation may be a critical time for cerebral hemodynamic disturbance leading to brain injury in preterm infants, particularly if they are exposed to inflammation in utero. We aimed to determine whether exposure to inflammation in utero alters cardiopulmonary hemodynamics, resulting in cerebral hemodynamic disturbance and related brain injury during the initiation of ventilation. Furthermore, we aimed to determine whether inflammation in utero alters the cerebral hemodynamic response to challenge induced by high mean airway pressures. Pregnant ewes received intra-amniotic lipopolysaccharide (LPS) or saline either 2 or 4-days before preterm delivery (at 128 ± 1 days of gestation). Lambs were surgically instrumented for assessment of pulmonary and cerebral hemodynamics before delivery and positive pressure ventilation. After 30 min, lambs were challenged hemodynamically by incrementing and decrementing positive end-expiratory pressure. Blood gases, arterial pressures, and blood flows were recorded. The brain was collected for biochemical and histological assessment of inflammation, brain damage, vascular extravasation, hemorrhage, and oxidative injury. Carotid arterial pressure was higher and carotid blood flow was more variable in 2-day LPS lambs than in controls during the initial 15 min of ventilation. All lambs responded similarly to the hemodynamic challenge. Both 2- and 4-day LPS lambs had increased brain interleukin (IL)-1β, IL-6, and IL-8 mRNA expression; increased number of inflammatory cells in the white matter; increased incidence and severity of brain damage; and vascular extravasation relative to controls. Microvascular hemorrhage was increased in 2-day LPS lambs compared with controls. Cerebral oxidative injury was not different between groups. Antenatal inflammation causes adverse cerebral hemodynamics and increases the incidence and severity of brain injury in ventilated preterm lambs.

Toll-like receptor 2 and facial motoneuron survival after facial nerve axotomy

We have previously demonstrated that CD4(+) Th2 lymphocytes are required to rescue facial motoneuron (FMN) survival after facial nerve axotomy through interaction with peripheral antigen presenting cells, as well as CNS resident microglia. Furthermore, the innate immune molecule, toll-like receptor 2 (TLR2), has been implicated in the development of Th2-type immune responses and can be activated by intracellular components released by dead or dying cells. The role of TLR2 in the FMN response to axotomy was explored in this study, using a model of facial nerve axotomy at the stylomastoid foramen in the mouse, in which blood-brain-barrier (BBB) permeability does not occur. After facial nerve axotomy, TLR2 mRNA was significantly upregulated in the facial motor nucleus and co-immunofluorescence localized TLR2 to CD68(+) microglia, but not GFAP(+) astrocytes. Using TLR2-deficient (TLR2(-/-)) mice, it was determined that TLR2 does not affect FMN survival levels after axotomy. These data contribute to understanding the role of innate immunity after FMN death and may be relevant to motoneuron diseases, such as amyotrophic lateral sclerosis (ALS).

Insulin-like growth factor I and II expression and modulation in amoeboid microglial cells by lipopolysaccharide and retinoic acid

Insulin-like growth factors I and II are known to regulate the development of the CNS. We examined the developmental changes in insulin-like growth factor I and insulin-like growth factor II expression in the postnatal rat corpus callosum. Insulin-like growth factor I and insulin-like growth factor II mRNA expression increased at 3 days as compared with 1 day whereas the protein expression increased up to 7 days. Insulin-like growth factor I and insulin-like growth factor II immunoexpression was specifically localized in round cells confirmed by double immunofluorescence with OX-42 to be the amoeboid microglial cells. Insulin-like growth factor I expression was observed up to 7 days in amoeboid microglial cells while insulin-like growth factor II expression was detected in 1-3 day old rats. Exposure of primary rat microglial cell cultures to lipopolysaccharide increased insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression significantly along with their immunoexpression in microglial cells. The lipopolysaccharide-induced increase in insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression was significantly decreased with all-trans-retinoic acid. We conclude that insulin-like growth factor I and insulin-like growth factor II expression in amoeboid microglial cells in the developing brain is related to their activation. Once the activation is inhibited, either by transformation of the amoeboid microglial cells into ramified microglia regarded as resting cells or as shown by the effect of all-trans-retinoic acid administration, insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression is downregulated.

Selective gene expression in brain microglia mediated via adeno-associated virus type 2 and type 5 vectors

Microglia represent a crucial cell population in the central nervous system, participating in the regulation and surveillance of physiological processes as well as playing key roles in the etiologies of several major brain disorders. The ability to target gene transfer vehicles selectively to microglia would provide a powerful new approach to investigations of mechanisms regulating brain pathologies, as well as enable the development of novel therapeutic strategies. In this study, we evaluate the feasibility of specifically and efficiently targeting microglia relative to other brain cells, using vectors based on two different serotypes of adeno-associated virus (AAV) carrying cell-type-specific transcriptional elements to regulate gene expression. Among a set of promoter choices examined, an element derived from the gene for the murine macrophage marker F4/80 was the most discriminating for microglia. Gene expression from vectors controlled by this element was highly selective for microglia, both in vitro and in vivo. To our knowledge, this is the first demonstration of selective expression of transferred genes in microglia using AAV-derived vectors, as well as the first utilization of recombinant AAV-5 vectors in any macrophage lineage. These results provide strong encouragement for the application of these vectors and this approach for delivering therapeutic and other genes selectively to microglia.

Interleukin-1beta promotes repair of the CNS

Interleukin-1beta (IL-1beta) is a proinflammatory cytokine associated with the pathophysiology of demyelinating disorders such as multiple sclerosis and viral infections of the CNS. However, we demonstrate here that IL-1beta appears to promote remyelination in the adult CNS. In IL-1beta(-/-) mice, acute demyelination progressed similarly to wild-type mice and showed parallel mature oligodendrocyte depletion, microglia-macrophage accumulation, and the appearance of oligodendrocyte precursors. In contrast, IL-1beta(-/-) mice failed to remyelinate properly, and this appeared to correlate with a lack of insulin-like growth factor-1 (IGF-1) production by microglia-macrophages and astrocytes and to a profound delay of precursors to differentiate into mature oligodendrocytes. Thus, IL-1beta may be crucial to the repair of the CNS, presumably through the induction of astrocyte and microglia-macrophage-derived IGF-1.

Mature oligodendrocyte apoptosis precedes IGF-1 production and oligodendrocyte progenitor accumulation and differentiation during demyelination/remyelination

We have documented changes in the oligodendrocyte population during demyelinating insult to the adult CNS. Feeding of cuprizone to adult mice led to apoptotic death of mature oligodendrocytes followed by profound demyelination of the corpus callosum. A regenerative response was initiated even during active demyelination. Oligodendrocyte progenitors have begun to proliferate and then accumulate within the lesion. Many of these cells may have migrated from the sub-ventricular zone and fornix before their accumulation in the demyelinating corpus callosum. The accumulation of differentiating oligodendrocyte progenitors was followed closely by the reappearance of mature oligodendrocytes and remyelination. Interestingly, an increase in IGF-1 mRNA was detected at Week 3 through Week 7, suggesting potential involvement in remyelination. Other factors, however, such as PDGF, NT3, FGF, jagged, and notch remained unchanged. These results suggest that the mature oligodendroglial population depleted by apoptosis is replaced by a newly formed oligodendroglial population derived from progenitors; these accumulate and seem to differentiate during remyelination.

Colonisation of the developing human brain and spinal cord by microglia: a review

Microglia are the immune effector cells of the nervous system. The prevailing view is that microglia are derived from circulating precursors in the blood, which originate from the bone-marrow. Colonisation of the central nervous system (CNS) by microglia is an orchestrated response during human fetal development related to the maturation of the nervous system. It coincides with vascularisation, formation of radial glia, neuronal migration and myelination primarily in the 4th-5th months and beyond. Microglial influx generally conforms to a route following white matter tracts to gray areas. We have observed that colonisation of the spinal cord begins around 9 weeks, with the major influx and distribution of microglia commencing around 16 weeks. In the cerebrum, colonisation is in progress during the second trimester, and ramified microglial forms are widely distributed within the intermediate zone by the first half of intra-uterine life (20-22 weeks). A distinct pattern of migration occurs along radial glia, white matter tracts and vasculature. The distribution of these cells is likely to be co-ordinated by spatially and temporally regulated, anatomical expression of chemokines including RANTES and MCP-1 in the cortex; by ICAM-2 and PECAM on radiating cerebral vessels and on capillaries within the germinal layer, and apoptotic cell death overlying this region. The phenotype and functional characteristics of fetal microglia are also outlined in this review. The need for specific cellular interactions and targeting is greater within the central nervous system than in other tissues. In this respect, microglia may additionally contribute towards CNS histogenesis.

Microglia in the human fetal spinal cord--patterns of distribution, morphology and phenotype

Microglia, the intrinsic macrophages of the nervous system, colonise the cerebrum around the second trimester in man. In order to determine the extent of microglial influx into the nervous system, we have examined their distribution within the human fetal spinal cord in relation to astrocytic and vascular development between 9 and 16 weeks of gestation, using conventional immunohistochemistry [CD11b; CD45; CD64; CD68; ICAM-1; ICAM-2; VCAM-1; PECAM; GFAP; vimentin] and lectin histochemistry [RCA-1]. Microglia are identifiable by 9 weeks, within the ventricular/sub-ventricular zones. Human fetal microglia display heterogeneity in phenotype and are more readily identified by CD68 in the spinal cord. There is a marked influx of cells dorsal and ventral to the neural cavity, from the marginal layer [meninges/connective tissue] with advancing gestational age, with greatest cell densities towards the end of the time period in this study. This inward migration is associated with progressive vascularisation, ICAM-2 expression and co-localises with GFAP and vimentin positive radial glia. The patterns of microglial migration in human fetal cord differ from that within the cerebrum, but generally conform to a route following white to gray matter.

Macrophages/microglial cells in human central nervous system during development: an immunohistochemical study

The development of microglia and macrophages was studied in 14 human embryos and fetuses ranging in age from 4.5-13.5 gestational weeks (g.w.), using lectins, Ricinus communis agglutinin-1 [RCA-1], and Lycopersicon esculentum, tomato lectin (TL), which recognize macrophages and microglia, and antibodies for the macrophage antigen CD68. Lectin-positive (+) cells were observed at 4.5 g.w., the youngest age examined. They were detected in the leptomeninges around the neural tube, and only rarely were observed in the CNS parenchyma. At 5.5 g.w., lectin+ cells were present throughout the CNS parenchyma, and a portion of these cells could also be labeled with antibody to CD68. In subsequent weeks, both types of cells, lectin+ and CD68+/lectin+ cells co-existed and progressively developed typical microglial morphology. In addition, in double label experiments, an antibody that labels CD14 antigen present on monocytes, hematogenous precursors of tissue macrophages, did not label either lectin+ or CD68+/lectin+ cells in CNS parenchyma. Additional immunocytochemical studies with appropriate markers excluded the possibility that any of the cells described here were either astrocytes, oligodendrocytes, endothelial cells or neurons. Our finding that one class of cells can be labeled early only with lectins, while another can be labeled with both lectins and CD68 macrophage antibody, may reflect a different origin of microglia in the early embryonic CNS compared to the fetal stages. This subdivision appears to be maintained in the adult brains as well.

Microglia in cell culture and in transplantation therapy for central nervous system disease

The central nervous system (CNS) is host to a significant population of macrophage-like cells known as microglia. In addition to these cells which reside within the parenchyma, a diverse array of macrophages are present in meningeal, perivascular, and other peripheral locations. The role that microglia and other CNS macrophages play in disease and injury is under intensive investigation, and functions in development and in the normal adult are just beginning to be explored. At present the biology of these cells represents one of the most fertile areas of CNS research. This article describes methodology for the isolation and maintenance of microglia in cell cultures prepared from murine and feline animals. Various approaches to identify microglia are provided, using antibody, lectin, or scavenger receptor ligand. Assays to confirm macrophage-like functional activity, including phagocytosis, lysosomal enzyme activity, and motility, are described. Findings regarding the origin and development of microglia and results of transplantation studies are reviewed. Based on these data, a strategy is presented that proposes to use the microglial cell lineage to effectively deliver therapeutic compounds to the CNS from the peripheral circulation.

Interactions of neurotrophic factors GDNF and NT-3, but not BDNF, with the immune system following fetal spinal cord transplantation

Glial cell line-derived neurotrophic factor (GDNF) is known to stimulate survival of dopaminergic and spinal cord motor neurons. However, little is known of the possible immune sequelae of GDNF exposure, or that of other putative trophic factors. To address these questions we utilized in oculo grafts of spinal cord, wherein we could induce different levels of immune responses via allogeneic vs. syngeneic combinations. Adult female Sprague-Dawley and Fisher rats were used as hosts for allogeneic and syngeneic grafts, respectively. Embryonic age 14-15-day-old fetuses were taken from pregnant dams of each strain, and cervical spinal cords were removed and dissected. Pieces of the spinal cord were transplanted into the anterior chamber of the eye within each strain. At 5-day intervals, 0.5 microgram of GDNF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) or cytochrome c (CC) was injected into the anterior chamber of the eye and the sizes of the transplants were measured for the Sprague-Dawley rats. The same injections and measurements, but only for GDNF and CC, were carried out using Fisher rats. As expected, GDNF increased transplant survival and growth in both the Sprague-Dawley and Fisher animals. At day 41-42, all rats were sacrificed. Cameral graft appearance was evaluated by cresyl violet and immunohistochemically using antibodies against neurofilament (NF), calcitonin gene-related peptide (CGRP) and glial fibrillary acidic protein (GFAP). To monitor immune responses, the following monoclonal antibodies were used: OX38 against CD4, OX18 against MHC class I (MHCI), OX8 against CD8, OX6 against MHC class II (MHCII), OX42 against CD11b, R73 against alpha and beta T cell receptor (TcR), and ED1. In the Sprague-Dawley grafts, significantly higher amounts of CD8+, T lymphocyte+, MHCI+ and MHCII+ antigen-presenting cells (APC) were observed in GDNF-treated transplants. These markers were also increased in NT-3-treated groups. There were two types of OX-42+ cells, one was the ordinary ramified microglial cell, the other appeared to be a phagocytic cell, looking like the interstitial proliferating variety. Interestingly, the phagocytic OX-42+ cells had the same distribution as ED1+ and MHCII+ cells. In contrast, there were few immunoreactive cells after GDNF treatment in the inbred Fisher animals, similar to the CC control group. These results suggest that GDNF and to some extent NT-3, can activate the immune system in allogeneic graft combinations, but that these trophic factors do not produce overt rejection, and do not per se induce immune responses.

Patterns of glial development in the human foetal spinal cord during the late first and second trimester

Although the presence of radial glia, astrocytes, oligodendrocytes and microglia has been reported in the human foetal spinal cord by ten gestational weeks, neuroanatomic studies employing molecular probes that describe the interrelated development of these cells from the late first trimester through the late second trimester are few. In this study, immunocytochemical methods using antibodies to vimentin and glial fibrillary acidic protein were used to identify radial glial and/or astrocytes. An antibody to myelin basic protein was used for oligodendrocytes and myelin; and, an antibody to phosphorylated high and medium molecular weight neurofilaments identified axons. Lectin histochemistry using Ricinus communis agglutinin-I was employed to identify microglia. Vibratome sections from 35 human foetal spinal cord ranging in age from 9-20 gestation weeks were studied. By 12 gestational weeks, vimentin-positive radial glia were present at all three levels of the spinal cord. Their processes were easily identified in the dorsal two-thirds of cord sections, and reaction product for vimentin was more intense at cervical and thoracic levels than lumbosacral sections. By 15 gestational weeks, vimentin-positive processes were radially arranged in the white matter. At this time, glial fibrillary acidic protein-positive astrocytes were more obvious in both the anterior and anterolateral funiculi than in the dorsal funiculus, and the same rostral to caudal gradient was seen for glial fibrillary acidic protein as it was for vimentin. Myelin basic protein expression followed similar temporal and spatial patterns. Ricinus communis agglutinin-I labelling revealed more microglia in the white matter than in grey matter throughout the spinal cord from 10-20 gestational weeks. By 20 gestational weeks, the gradients of glial fibrillary acidic protein and vimentin expression were more difficult to discern. White matter contained more microglia than grey matter. These results suggest that astrocytes as well as oligodendrocytes follow anterior-to-posterior and rostral-to-caudal developmental patterns in the human foetus during middle trimester development.

Identification of Fc gamma RI, II and III on normal human brain ramified microglia and on microglia in senile plaques in Alzheimer's disease

Using monoclonal antibodies to the three known human leukocyte IgG receptors, Fc gamma R, we examined the expression of Fc gamma R in normal brains and in Alzheimer's disease. We found Fc gamma RI, II and III immunoreactivity in senile plaques and on ramified microglia throughout the cortex and white matter of normal and Alzheimer's disease brains. Fc gamma RI expression was independently confirmed by a murine isotype binding study. These findings suggest that intrinsic Fc gamma R may play an important role in normal and disordered immune-related processes in the brain. They support the idea that microglia are brain macrophages.

Perinatal AIDS: drugs of abuse and transplacental infection

The number of children infected by the human immunodeficiency virus type-1 (HIV-1) who develop the acquired immunodeficiency syndrome (AIDS) continues to increase. While some children become infected after birth and others at the time of parturition, a significant percentage are infected during gestation and there is a positive correlation between maternal illicit intravenous drug use and fetal HIV-1 infection. Drugs can contribute in, at least, four ways to vertical transmission of HIV-1. These four ways are divisible into 2 main categories that are comprised of both direct and indirect mechanisms. For example, drugs of abuse can have a direct effect on the maternal-fetal interface. Cocaine is associated with vasculitis. If this occurs as a placentitis or chorioamnionitis, it can alter the permeability of these barriers to maternal blood and increase the number of potentially infected inflammatory cells in this tissue and as a result in the fetus. Another direct mechanism wherein drugs of abuse can increase the probability that a fetus will become infected is via an inflammatory reaction such as a vasculitis in the fetus rendering it more susceptible to viral infection. Drugs can also affect the course of HIV-1 infection via indirect mechanisms. An example of this may be by modulating the female immune system. This effect can exacerbate the woman's immunodeficiency and accelerate opportunistic infections. For example, cytomegalovirus infection resulting in placentitis might facilitate fetal HIV-1 infection. Lastly, a similar type of indirect mechanism can be postulated for the fetus wherein its developing immune system can be adversely effected.(ABSTRACT TRUNCATED AT 250 WORDS)