The decreasedin vitro chemotactic activity of polymorphonuclear leukocytes of newborns and infants

Using Boyden's technique, a statistically significant decrease in the chemotactic activity of polymorphonuclear (PMN) leukocytes was found during the early postnatal period, i.e. in the cord blood and in blood of newborns within the first 10-15 d of life after stimulation of cells with both zymosan-activated adult serum (ZAS) and with an abacterial filtrate of Escherichia coli broth culture (ECF). After this period, the responsiveness of leukocytes to both chemotactic agents increased and remained at the same level during the whole observation period, i.e. up to the age of 6 months. Nevertheless even then it did not reach fully the responsiveness of the leukocytes of mothers and pregnant women. Zymosan-activated serum was shown to be a more potent chemotactic stimulus to leukocytes of infants as compared to the E. coli filtrate.     

Innate immune deficiency of extremely premature neonates can be reversed by interferon-γ

Background

Bacterial sepsis is a major threat in neonates born prematurely, and is associated with elevated morbidity and mortality. Little is known on the innate immune response to bacteria among extremely premature infants.

Methodology/Principal Findings

We compared innate immune functions to bacteria commonly causing sepsis in 21 infants of less than 28 wks of gestational age, 24 infants born between 28 and 32 wks of gestational age, 25 term newborns and 20 healthy adults. Levels of surface expression of innate immune receptors (CD14, TLR2, TLR4, and MD-2) for Gram-positive and Gram-negative bacteria were measured in cord blood leukocytes at the time of birth. The cytokine response to bacteria of those leukocytes as well as plasma-dependent opsonophagocytosis of bacteria by target leukocytes was also measured in the presence or absence of interferon-γ. Leukocytes from extremely premature infants expressed very low levels of receptors important for bacterial recognition. Leukocyte inflammatory responses to bacteria and opsonophagocytic activity of plasma from premature infants were also severely impaired compared to term newborns or adults. These innate immune defects could be corrected when blood from premature infants was incubated ex vivo 12 hrs with interferon-γ.

Conclusion/Significance

Premature infants display markedly impaired innate immune functions, which likely account for their propensity to develop bacterial sepsis during the neonatal period. The fetal innate immune response progressively matures in the last three months in utero. Ex vivo treatment of leukocytes from premature neonates with interferon-γ reversed their innate immune responses deficiency to bacteria. These data represent a promising proof-of-concept to treat premature newborns at the time of delivery with pharmacological agents aimed at maturing innate immune responses in order to prevent neonatal sepsis.     

Microfluidic skin chip with vasculature for recapitulating the immune response of the skin tissue

There is a considerable need for cell-based in vitro skin models for studying dermatological diseases and testing cosmetic products, but current in vitro skin models lack physiological relevance compared to human skin tissue. For example, many dermatological disorders involve complex immune responses, but current skin models are not capable of recapitulating the phenomena. Previously, we reported development of a microfluidic skin chip with a vessel structure and vascular endothelial cells. In this study, we cocultured dermal fibroblasts and keratinocytes with vascular endothelial cells, human umbilical vascular endothelial cells. We verified the formation of a vascular endothelium in the presence of the dermis and epidermis layers by examining the expression of tissue-specific markers. As the vascular endothelium plays a critical role in the migration of leukocytes to inflammation sites, we incorporated leukocytes in the circulating media and attempted to mimic the migration of neutrophils in response to external stimuli. Increased secretion of cytokines and migration of neutrophils was observed when the skin chip was exposed to ultraviolet irradiation, showing that the microfluidic skin chip may be useful for studying the immune response of the human tissue.     

Leukocyte procoagulant activity in man: an in vitro correlate of delayed-type hypersensitivity

Human mononuclear leukocytes generate cell-bound procoagulant activity (LPCA) after incubation with an antigen (mumps or tuberculin) to which the donor was previously sensitized. An inhibitor of coagulation appears to be liberated into the extracellular culture fluid during incubation of leukocytes with the sensitizing antigen. Removal of this activity before measuring LPCA resulted in a reliable test that correlated directly with delayed skin reactivity. The assay was particularly sensitive in that cells from weakly sensitized donors who reacted only to high doses of tuberculin (100 TU) in the delayed skin tests produced detectable LPCA in vitro. By contrast cells from weakly sensitized donors did not react to PPD in the lymphocyte blast transformation test or the direct macrophage migration inhibition factor test. The LPCA assay correlated closely with the blast transformation and MIF tests in which cells were used from more strongly sensitized donors who reacted in skin tests with lower doses of tuberculin (1 or 10 TU). The assays were antigen-specific in that cells from donors sensitive to mumps antigen but not to tuberculin reacted only to mumps antigen in vitro. The assay was extremely reproducible; cells from individual donors reacted to the same extent over a period of 8 mo). We propose that the assay system reported here represents an improved method for the measurement of cell-mediated immunity in vitro because it requires fewer donor cells, is technically simpler, and is more sensitive than previously described methods.     

Neurotransmitters are regulators for the migration of tumor cells and leukocytes

Neurotransmitters are signal substances that have traditionally been regarded as mere mediators of signal states between cells in the nervous system. Whereas the mechanisms of this "classic" neurotransmitter regulation are well understood, only recently has new evidence come to light elucidating the modulatory role of neurotransmitters in immune function, and in the regulation of migration of leukocytes and tumor cells. The migration of leukocytes is, among other things, of primary importance for an anti-tumor immune response, whereas the migration of tumor cells is a prerequisite for invasion and the development of metastases. We here clarify and consolidate the latest tumor biological findings on the role of these neurotransmitters, which bind to serpentine receptors, and which are involved in leukocyte migration, tumor growth, invasion and metastasis. This review thus accentuates the complex, interactive involvement of neurotransmitters in the regulation of migration of both leukocytes and tumor cells.     

The neutrophil response to polyvinyl sponge implantation

Neutrophil release and migration in mice were studied over a 24-hr period after the sc implantation of a single polyvinyl sponge. The release of neutrophils from the marrow was evaluated by directly counting the residual neutrophils in the femoral marrow of animals with sponges. Sponge and tissue neutrophil content was determined by extraction and assay of myeloperoxidase (MPO), a marker enzyme for neutrophils. A maximum depletion of 48% of the mature neutrophils in the marrow was observed 5 hr after sponge implantation, in keeping with significant release of neutrophils for migration to the sponge. The released cells were not found in the circulating granulocyte pool, since neutropenia was noted. The accumulation of neutrophils in the sponge increased throughout the 24-hr period, whereas in the tissue adjacent to the sponge maximum accumulation of neutrophils occurred within 7 hr. In fact, neutrophils migrated to at least three sites--the sponge, the skin overlying the sponge, and the skin in which an incision had been made to insert the sponge. The sponge content of neutrophils represented 0.3-33% of the neutrophils migrating to the combined lesion (sponge and skin sites). Therefore, if the neutrophil response to foreign body implantation is to be measured in its entirety, it is necessary to quantify not only the neutrophils within the foreign body but also those in the tissues surrounding it. These studies describe an animal model for neutrophil release and migration to tissues following a standard stimulus. It is proposed that this model may be useful in exploring the factors which influence the release and migration of neutrophils in vivo.     

Dermal dendritic cells, and not Langerhans cells, play an essential role in inducing an immune response

Langerhans cells (LCs) serve as epidermal sentinels of the adaptive immune system. Conventional wisdom suggests that LCs encounter Ag in the skin and then migrate to the draining lymph nodes, where the Ag is presented to T cells, thus initiating an immune response. Platelet-activating factor (PAF) is a phospholipid mediator with potent biological effects. During inflammation, PAF mediates recruitment of leukocytes to inflammatory sites. We herein tested a hypothesis that PAF induces LC migration. Applying 2,4-dinitro-1-fluorobenzene (DNFB) to wild-type mice activated LC migration. In contrast, applying DNFB to PAF receptor-deficient mice or mice injected with PAF receptor antagonists failed to induce LC migration. Moreover, after FITC application the appearance of hapten-laden LCs (FITC+, CD11c+, Langerin+) in the lymph nodes of PAF receptor-deficient mice was significantly depressed compared with that found in wild-type mice. LC chimerism indicates that the PAF receptor on keratinocytes but not LCs is responsible for LC migration. Contrary to the diminution of LC migration in PAF receptor-deficient mice, we did not observe any difference in the migration of hapten-laden dermal dendritic cells (FITC+, CD11c+, Langerin-) into the lymph nodes of PAF receptor-deficient mice. Additionally, the contact hypersensitivity response generated in wild-type or PAF receptor-deficient mice was identical. Finally, dermal dendritic cells, but not LCs isolated from the draining lymph nodes after hapten application, activated T cell proliferation. These findings suggest that LC migration may not be responsible for the generation of contact hypersensitivity and that dermal dendritic cells may play a more important role.     

Dendritic Cell Migration Limits the Duration of CD8+ T-Cell Priming to Peripheral Viral Antigen

CD8⁺ T cells (T_CD8⁺) play a crucial role in immunity to viruses. Antiviral T_CD8⁺ are initially activated by recognition of major histocompatibility complex (MHC) class I-peptide complexes on the surface of professional antigen-presenting cells (pAPC). Migration of pAPC from the site of infection to secondary lymphoid organs is likely required during a natural infection. Migrating pAPC can be directly infected with virus or may internalize antigen derived from virus-infected cells. The use of experimental virus infections to assess the requirement for pAPC migration in initiation of T_CD8⁺ responses has proven difficult to interpret because injected virus can readily drain to secondary lymphoid organs without the need for cell-mediated transport. To overcome this ambiguity, we examined the generation of antigen-specific T_CD8⁺ after immunization with recombinant adenoviruses that express antigen driven by skin-specific or ubiquitous promoters. We show that the induction of T_CD8⁺ in response to tissue-targeted antigen is less efficient than the response to ubiquitously expressed antigen and that the resulting T_CD8⁺ fail to clear all target cells pulsed with the antigenic peptide. This failure to prime a fully functional T_CD8⁺ response results from a reduced period of priming to peripherally expressed antigen versus ubiquitously expressed antigen and correlated with a brief burst of pAPC migration from the skin, a requirement for induction of the response to peripheral antigen. These results indicate that a reduced duration of pAPC migration after virus infection likely reduces the amplitude of the T_CD8⁺ response, allowing persistence of the peripheral virus.The induction of effector CD8⁺ T cells (T_CD8⁺) is a vital step in the eradication or control of many viral infections. The induction of antiviral T_CD8⁺ requires the presentation of virally derived peptides in complex with major histocompatibility complex (MHC) class I on the surface of specialized professional antigen-presenting cells (pAPC), most commonly a subset of dendritic cells (DC) that bear the CD8α chain (1, 29). The CD8α⁺ DC reside only in secondary lymphoid organs and not in the tissues, implying that cell-mediated transport or drainage of virus particles to a lymph node is required for initiation of a T_CD8⁺ response. Partial inhibition of DC migration from the skin can impair the initiation of a T_CD8⁺ response (2). After influenza infection in the lungs, there is a burst of DC migration, followed by a refractory period in which no DC migration occurs (19). The functional consequences of this refractory period of DC migration have not been explored.A number of viruses, particularly human papillomaviruses, infect the skin and are ignored by the immune response for extended periods of time (31). We sought to explore the possibility that, after a low-level peripheral virus infection of the skin, changes in DC migration may limit the availability of antigen in the draining lymph node and thus the induction of a T_CD8⁺ response. There are a number of confounding factors that make the study of DC migration in the initiation of an antiviral T_CD8⁺ response difficult. Virus particles may directly drain to the lymph node within seconds (11, 13, 25). In addition, many viruses will alter DC functions, including migration, after infection of the DC itself. This may occur via specific viral modulation of DC function (16) or via nonspecific shut down of host protein synthesis (26), both of which will affect migration. Thus, it is often not possible to distinguish between the effects of virus infection upon DC migration, drainage of virus directly to the lymph node, and the natural response that follows migration of DC responding to a peripheral virus infection.There is currently no mouse model of a peripheral virus infection that is confined to the skin, as no natural mouse papillomavirus has ever been isolated. Therefore, to address these issues, we have made use of another small DNA virus, namely, an adenovirus vector that is replication deficient (rAd). These vectors express influenza virus nucleoprotein (NP) under the control of a ubiquitous (cytomegalovirus [CMV] immediate-early) or tissue-targeted promoter (K14, targeted to keratinocytes, the site of papillomavirus replication). Antigen driven by the K14 promoter is expressed only in skin cells, so only uninfected DC can present antigen in this system, removing the need to account for modulation of the function of virus-infected DC.We demonstrate that when antigen is expressed in only keratinocytes in the skin, the efficiency of T_CD8⁺ induction is reduced and the time period for which antigen is available to prime effector cells is reduced dramatically. DC-mediated transport is required for antigen to reach the lymph node where a T_CD8⁺ response is initiated. The reduced time period of antigen presentation is the result of a transient blockade in DC migration from the site of infection. The blockade in DC migration reduced the delivery of viral antigen to the lymph node needed to induce a T_CD8⁺ response. The resulting T_CD8⁺ response to peripheral viral antigen is not capable of clearing all target cells presenting a viral peptide, thus allowing the persistence of peripheral virus-infected cells. These results provide a potential mechanism for the long-term evasion of the immune response by papillomaviruses following natural infection and also have important implications for tissue targeted gene therapy vectors.     

Factor associated with neutral sphingomyelinase activity mediates navigational capacity of leukocytes responding to wounds and infection: live imaging studies in zebrafish larvae

Factor associated with neutral sphingomyelinase activity (FAN) is an adaptor protein that specifically binds to the p55 receptor for TNF (TNF-RI). Our previous investigations demonstrated that FAN plays a role in TNF-induced actin reorganization by connecting the plasma membrane with actin cytoskeleton, suggesting that FAN may impact on cellular motility in response to TNF and in the context of immune inflammatory conditions. In this study, we used the translucent zebrafish larvae for in vivo analysis of leukocyte migration after morpholino knockdown of FAN. FAN-deficient zebrafish leukocytes were impaired in their migration toward tail fin wounds, leading to a reduced number of cells reaching the wound. Furthermore, FAN-deficient leukocytes show an impaired response to bacterial infections, suggesting that FAN is generally required for the directed chemotactic response of immune cells independent of the nature of the stimulus. Cell-tracking analysis up to 3 h after injury revealed that the reduced number of leukocytes is not due to a reduction in random motility or speed of movement. Leukocytes from FAN-deficient embryos protrude pseudopodia in all directions instead of having one clear leading edge. Our results suggest that FAN-deficient leukocytes exhibit an impaired navigational capacity, leading to a disrupted chemotactic response.     

Migration of Langerhans cells and gammadelta dendritic cells from UV-B-irradiated sheep skin

Depletion of dendritic cells from UV-B-irradiated sheep skin was investigated by monitoring migration of these cells towards regional lymph nodes. By creating and cannulating pseudoafferent lymphatic vessels draining a defined region of skin, migrating cells were collected and enumerated throughout the response to UV-B irradiation. In the present study, the effects of exposing sheep flank skin to UV-B radiation clearly demonstrated a dose-dependent increase in the migration of Langerhans cells (LC) from the UV-B-exposed area to the draining lymph node. The range of UV-B doses assessed in this study included 2.7 kJ/m2, a suberythemal dose; 8 kJ/m2, 1 minimal erythemal dose (MED); 20.1 kJ/m2; 40.2 kJ/m2; and 80.4 kJ/m2, 10 MED. The LC were the cells most sensitive to UV-B treatment, with exposure to 8 kJ/m2 or greater reproducibly causing a significant increase in migration. Migration of gammadelta+ dendritic cells (gammadelta+ DC) from irradiated skin was also triggered by exposure to UV-B radiation, but dose dependency was not evident within the range of UV-B doses examined. This, in conjunction with the lack of any consistent correlation between either the timing or magnitude of migration peaks of these two cell types, suggests that different mechanisms govern the egress of LC and gammadelta+ DC from the skin. It is concluded that the depression of normal immune function in the skin after exposure to erythemal doses of UV-B radiation is associated with changes in the migration patterns of epidermal dendritic cells to local lymph nodes.     

Changes in Glutathione Peroxidase Activities and the Oxidative Burst of Leukocytes During Inflammation in the Mouse and Rat

The relationship between glutathione peroxidase (GSH-Px) activity and opsonized zymosan-induced chemiluminescence (CL) has been studied with exudate leukocytes obtained at different times after induction of inflammatory responses in the mouse peritoneal cavity with heat-killed Corynebacterium parvum and in the rat pleural cavity with I-carrageenin. GSH-Px activity in mouse peritoneal exudate cells fell markedly after 2–4h, returning to normal within 1–2 days. The lowered enzyme activity was associated with an increased ability of the cells to generate CL. Rat pleural exudate cells exhibited a slight fall in GSH-Px activity after 6h which increased to supranormal levels within 1–2 days. During this period the ability of the cells to generate CL continually increased. The data indicate that during the early phase of increased generation of reactive oxygen species (ROS) by inflammatory leukocytes, the intracellular protective mechanism, represented by GSH-Px, is compromised. Subsequently, GSH-Px activity increases to or above initial levels possibly due to the presence of mononuclear cells and/or as a response to the increased generation of ROS.     

Production of migration inhibitory factor (MIF) by human leukocytes following exposure to Epstein-Barr virus.

The ability of Epstein-Barr virus (EBV) to induce a cell-mediated immune response (CMI) in cultures of human leukocytes was investigated. Partially purified EBV, obtained from culture fluids of AV-1 cells, was inactivated by uv-irradiation. Inactivated virus was mixed with peripheral leukocytes from Hodgkin's disease (HD), infectious mononucleosis (IM) and malignant lymphoma patients as well as from normal individuals in an in vitro culture system. Production of migration inhibitory factor (MIF), as measured by guinea pig macrophage migration inhibition (MMI), was utilized as an indicator of CMI response. Significant differences in MIF response were observed subsequent to exposure of the cells to EBV. Leukocytes from patients in each of the disease categories tested exhibited greater MIF production than did those from the normal controls. There were significant differences in MIF production by leukocytes from the malignant and non-malignant disease categories. Serum from each subject was examined for immunoglobulin specific for EBV capsid antigen (anti-VCA). Although the majority of individuals within the disease categories tested had elevated anti-EBV serum titers, no correlation could be made between elevated anti-VCA titer and levels of MIF production.     

Population-demographic structure of the population of Kursk region: anthropometric profile of newborn children

Based on the characteristics of body height and weight in 4905 newborns, the population-genetic structure of the rural raions (districts) of Kursk oblast (region) and in the city of Kursk was determined. An "adaptive norm area" with respect to body weight and height was distinguished for newborns in Kursk oblast. On the average, the anthropometric parameters of 20% of infants from the studied populations fell within this area. The height and growth of newborns exhibited a pronounced geographic variation and depended on the level of urbanization, as well as the sex and the health status of the newborns. In district populations, the body height and the variances of the body height and weight increased with an increase in endogamy. Therefore, the relative numbers of newborns with large values of both weight and height, as well as those with a medium body height and a small body weight, were increased. Conversely, the relative numbers of newborns with a low weight and height and with a disturbed weight-height correlation were decreased.     

Ultrastructure and peroxidase cytochemistry of normal human leukocytes at birth

At birth, differential and white blood cell counts of normal newborn infants are strikingly different from those of adults in that the number of leukocytes is increased and immature cells course through the circulation. In this study, our intent was to examine normal neonatal cord blood by electron microscopy and peroxidase cytochemistry to determine whether any detectable differences exist in the leukocytes of neonatal and adult blood. This investigation was undertaken because newborn infants have an increased susceptibility to infection, and alterations in phagocyte function have been implicated as the cause. Cord blood was found to contain mature leukocytes of all kinds, similar in ultrastructure and peroxidase localization to those of adults. Moreover, as indicated earlier by light microscopy, immature forms (normally found only in adult bone marrow) were present in the blood of newborns. We found that nearly all cell lines were represented in the neonatal circulation by such developmental forms as promyelocytes, myelocytes, promonocytes, erythroblasts, megakaryocytes, rare unidentifiable blasts, and dividing cells—all resembling their counterparts in adult bone marrow. With the techniques used here, neonatal leukocytes were similar to those of the adult in ultrastructure and peroxidase localization, although some had been mobilized into the blood in a remarkably immature state. This study, the first of its kind, will serve as a helpful background for future investigations of acquired, genetic or neoplastic leukocyte abnormalities which may be discovered at birth.     

Antibody-dependent cytolytically active human leukocytes: an analysis of inactivation following in vitro interaction with antibody-coated target cells.

A leukocyte population consisting of approximately 85% lymphocytes, prepared from human peripheral blood by centrifugation through a Ficoll-Hypaque gradient, was studied for its capacity to destroy antibody-coated human liver (Chang) cells in vitro. Cytolysis was a rapid event: increased ionic flux (86Rb) from the target cell occurred within 10 min of the addition of effector cells. Kinetic analysis of target cell destruction (51 Cr release) was compatible with a "one hit" hypothesis, thereby indicating that cytolysis resulted from a single collision was an effector cell. The initial rate of cytolysis was linear and related to the number of leukocytes added, but lysis at all of the leukocyte to target cell ratios tested ceased after 5 hr. The number of target cells killed at that time was directly proportional to the number of leukocytes added. While the lytic capacity of the effector population was totally depleted after incubation with antibody-coated target cells, cytotoxicity was not affected by co-culturing leukocytes with Chang cells treated with pre-immune serum. The cytotoxic effector cells functioning in this antibody-dependent lytic system are thus to be contrasted with killer T cells, whose lytic activity is not compromised by interaction with homologous target cells. It was estimated that approximately 4% of the leukocyte population employed could kill antibody-coated Chang cells, a figure consistent with the estimated frequency of "null" cells within human peripheral lymphocytes.     

Platelet release products modulate some aspects of polymorphonuclear leukocyte activation.

The aim of this research was to evaluate in vitro interactions between platelets and polymorphonuclear leukocytes. The effects of supernatant from thrombin-activated platelets and two platelet release products (adenosine triphosphate and beta-thromboglobulin) were tested on the following features of polymorphonuclear leukocytes activation: opsonized zymosan and phorbol myristate acetate stimulated chemiluminescence, release of membrane bound calcium, NADPH-oxidase activity, and membrane fluidity (fluorescent polarization). The results showed that the addition of platelet supernatant to polymorphonuclear leukocytes induces a significant activation of cells. On the other hand, after three hours of preincubation of polymorphonuclear leukocytes with platelet supernatant, a decreased response of polymorphonuclear leukocytes to stimulation with phorbol myristate acetate, a significant decrease in NADPH-oxidase activity, and a lowered membrane fluidity were observed. Adenosine triphosphate modulated only opsonized zymosan stimulated chemiluminescence, with and without preincubation with polymorphonuclear leukocytes. Beta-thromboglobulin caused a decrease of the chemiluminescent response of polymorphonuclear leukocytes, using both agonists, with and without preincubation with polymorphonuclear leukocytes. Moreover beta-thromboglobulin only caused a decrease of the polymorphonuclear leukocytes membrane fluidity without preincubation with the cells. These results support the thesis that platelets have a "time-related" modulating activity on polymorphonuclear leukocytes.     

Inflammatory process caused by intraperitoneal injection of polyester in the rat: chemotactic activity in lavage fluid from the cavity

Minced polyester threads introduced into peritoneal cavity of guinea pigs or rats cause a granulomatous inflammation with evidence of macrophage stimulation. Chemotactic agents play an important role in the inflammatory reaction; they may be exogenous and/or endogenous. These are released locally by the cells involved in inflammation. In this paper the chemotactic effects of the peritoneal fluids from rats bearing the polyester inflammatory process, have been studied on PMN cells "in vitro". The peritoneal cavity fluids were obtained by washing the cavity of untreated rats or rats intraperitoneally injected with polyester, 1, 3, 7, 14 days after the intraperitoneal injection. The chemotactic response was assayed by employing modified chemotaxis Boyden chambers (Blind Well Neuro Probe) and polymorphonuclear leukocytes from normal or treated rats. Quantification of the migration was calculated by chemotactic index (A/B) (B = random migration, A = chemotaxis). The results demonstrated that the peritoneal fluids taken 3 and 7 days after the intraperitoneal polyester injection, elicit an evident chemotaxis response greater than that showed by peritoneal fluids from control rats. It is suggested that chemotactic factors can be produced and released by mononuclear cells involved in the inflammatory process.     

Organotypic Culture of Human Skin to Study Melanocyte Migration

An ex vivo model system was developed to investigate melanocyte migration. Within this model system, melanocytes migrate among other epidermal cells in the epibolic outgrowth of skin explants. This process is initiated by loss of contact inhibition of epidermal cells at the rim of the explants and by locally produced chemotactic factors. Punch biopsies provided explants of reproducible diameter. Optimal culture conditions include medium consisting of Dulbecco's Minimal Essential Medium containing 10% inactivated normal human serum and placement of explants epidermal side up at the air-liquid interphase. Within 7 days, epidermal cells completely surround the explant. Approximately 3 days after the onset of keratinocyte migration, melanocytes distribute themselves within the newly formed epidermis. Throughout the 7-day culture period, melanocytes and keratinocytes show maintenance of subcellular morphology, and the dermo-epidermal junction remains intact. Melanocyte migration was quantified using immunoperoxidase staining in combination with light microscopy and computer-aided image analysis. Preliminary results using the model system to compare migration in control and nonlesional vitiligo skin indicate that no inherent migration defect is responsible for impaired repigmentation of vitiligo lesions. The organotypic culture model system allows for investigations on melanocytes within their environment of autologous epidermal and dermal components, closely resembling in vivo circumstances in human skin.     

Control of Surface Wound Infection: Skin Versus Synthetic Grafts

Auto-, iso-, or xenografts of skin and synthetics placed on surface wounds freshly contaminated with Pseudomonas aeruginosa stabilizes the wound bacterial population in rats over a 24-h period. When these wounds contained a bacterial contamination established for 24 h prior to grafting, only skin and the synthetic polyhydroxyethylmethacrylate were effective in lowering the initial bacterial concentration. Polyurethane foam and nylon velour were not effective in the established infection model. Skin placed on a contaminated wound for 2 h or longer appeared to equilibrate with the underlying muscle so that the bacterial count per milligram of skin was similar to that of the muscle. It was suggested that this preparation would be useful to obtain an estimate of surface contamination without biopsy of the infected muscle. Skin grafts in place for 2 h significantly lowered the bacterial count in a wound with an established infection. A second decrease occurred between 4 and 24 h after grafting. Histological studies of contaminated and exposed panniculus muscle showed that leukocytes tend to migrate from the muscle surface to its base. Skin grafts and polyhydroxyethylmethacrylate appear to reverse the white cell migration so that the cells move toward the surface of the muscle with preservation of normal staining characteristics in the muscle. It is suggested that this alteration in cell movement after graft application might modify the white cell function and result in a greater bactericidal activity. Apparently, grafts lower bacterial levels in an established infection by modifying the host response to the surface contamination.     

Pseudopod projection and cell spreading of passive leukocytes in response to fluid shear stress

Recent evidence suggests that circulating leukocytes respond to physiological levels of fluid shear stress. This study was designed to examine the shear stress response of individual leukocytes adhering passively to a glass surface. Human leukocytes were exposed to a step fluid shear stress with amplitude between 0.2 and 4 dyn/cm(2) and duration between 1 and 20 min. The response of the cells was determined in the form of projected cell area measurements by high-resolution observation before, during, and after fluid shear application. All cells selected initially had a round morphology. After application of fluid shear many cells projected pseudopodia and spread on the glass surface. The number of leukocytes responding with pseudopod projection and the extent of cell spreading increased with increasing amplitude and duration of fluid shear stress. Pseudopod projection after exposure to a step fluid shear occurs following a delay that is insensitive to the shear stress amplitude and duration. Leukocytes that did not project pseudopodia and spread in response to low shear stress could be shown to respond to a second shear step of higher amplitude. The spreading response requires an intact actin network and activated myosin molecules. Depleting the cell glycocalyx with protease treatment enhances the spreading response in sheared leukocytes. These results indicate that passive leukocytes respond to fluid shear stress with active pseudopod projection and cell spreading. This behavior may contribute to cell spreading on endothelium and other cells as well as to transendothelial migration of leukocytes in the microcirculation.