Salivary Cortisol and Anxiety in Canadian Dentists over 1 Year of COVID-19

The dental profession has endured unprecedented disruption amid COVID-19. Novel stressors have included a high risk of occupational exposure to COVID-19, financial losses, and stricter infection prevention and control requirements. The present study investigated the longitudinal impact of COVID-19 on the stress and anxiety levels of a cohort of Canadian dentists (N = 222) between September 2020 and October 2021. Salivary cortisol was selected as a biomarker of mental stress, and 10 sets of monthly saliva samples (2,131 in total) were self-collected, sent to our laboratory in prepaid courier envelopes, and analyzed by enzyme-linked immunosorbent assay. To assess COVID-19 anxiety, 9 monthly online questionnaires were administered, comprising a general COVID-19 anxiety instrument and 3 items regarding the impact of dentistry-related factors. Bayesian log-normal mixed effect models were fitted to estimate the longitudinal trajectory of salivary cortisol levels and their association with the disease burden of COVID-19 in Canada. After accounting for age, sex, vaccination status, and the diurnal rhythm of cortisol secretion, a modest positive association was found between dentists' salivary cortisol levels and the count of COVID-19 cases in Canada (96% posterior probability). Similarly, the self-reported impact of dentistry-related factors, such as fear of getting COVID-19 from a patient or coworker, was greatest during peaks of COVID-19 waves in Canada; however, general COVID-19 anxiety decreased consistently throughout the study period. Interestingly, at all collection points, the majority of participants were not concerned about personal protective equipment. Overall, participants reported relatively low rates of psychological distress symptoms in relation to COVID-19, a result that should be reassuring for the dental community. Our findings strongly suggest a link between self-reported and biochemical measurements of stress and anxiety in Canadian dentists during the COVID-19 pandemic.

Periodontal Inflammation Primes the Systemic Innate Immune Response

The presence of periodontal diseases (PDs) often strongly correlates with other severe chronic inflammatory conditions, including cardiovascular disease, diabetes, and arthritis. However, the mechanisms through which these diseases interact are unclear. In PD, tissue and bone destruction in the mouth is driven by elevated recruitment of polymorphonuclear neutrophils (PMNs), which are primed and recruited from the circulation to sites of inflammation. We predicted that systemic effects on PMN mobilization or priming could account for the interaction between PD and other inflammatory conditions. We tested this using a mouse model of ligature-induced PD and found elevated PMN counts specifically in bone marrow, supporting a systemic effect of periodontal tissue inflammation on PMN production. In contrast, mice with induced peritonitis had elevated PMN counts in the blood, peritoneum, and colon. These elevated counts were further significantly increased when acute peritonitis was induced after ligature-induced PD in mice, revealing a synergistic effect of multiple inflammatory events on PMN levels. Flow cytometric analysis of CD marker expression revealed enhanced priming of PMNs from mice with both PD and peritonitis compared to mice with peritonitis alone. Thus, systemic factors associated with PD produce hyperinflammatory PMN responses during a secondary infection. To analyze this systemic effect in humans, we induced gingival inflammation in volunteers and also found significantly increased activation of blood PMNs in response to ex vivo stimulation, which reverted to normal following resolution of gingivitis. Together, these results demonstrate that periodontal tissue inflammation has systemic effects that predispose toward an exacerbated innate immune response. This indicates that peripheral PMNs can respond synergistically to simultaneous and remote inflammatory triggers and therefore contribute to the interaction between PD and other inflammatory conditions. This suggests larger implications of PD beyond oral health and reveals potential new approaches for treating systemic inflammatory diseases that interact with PD.

The Biology of Social Adversity Applied to Oral Health

Biological embodiment is a concept derived from Engel's biopsychosocial model to health, theorized as the process by which adverse social exposures trigger neuroendocrine and immune responses, leading to disease and/or increased disease susceptibility. This critical review discusses the biopsychosocial model as applied to oral health and its relevance to oral health policy while deciphering some of the pathobiological processes underlying social adversity. In periodontal disease, for example, such processes can occur via the activation of the hypothalamic-pituitary-adrenal axis and the consequent release of the chronic stress hormone cortisol. The latter contributes to a proinflammatory immune state that increases the risk for periodontal inflammation. Recent research shows that cortisol relates to an elevated oral inflammatory load, demonstrated as hyperactive neutrophils that are pivotal to periodontal tissue damage. Consistent with the biopsychosocial model, this relationship is amplified in those of lower income and higher financial stress. Similarly, among children from lower socioeconomic backgrounds, cortisol is linked to a higher cariogenic bacterial load. Such findings implicate the stress pathway as key in the oral pathogenic process, particularly under social/socioeconomic adversity. Collectively, this work emphasizes the importance of addressing social factors in alleviating oral disease burden and reducing the social gaps therein.

Resolving Macrophages Counter Osteolysis by Anabolic Actions on Bone Cells

Progression of inflammatory osteolytic diseases, including rheumatoid arthritis and periodontitis, is characterized by increased production of proinflammatory mediators and matrix-degrading enzymes by macrophages and increased osteoclastic activity. Phenotypic changes in macrophages are central to the healing process in virtually all tissues. Using a murine model of periodontitis, we assessed the timing of macrophage phenotypic changes and the impact of proresolving activation during inflammatory osteolysis and healing. Proinflammatory macrophage activation and TNF-α overproduction within 3 wk after induction of periodontitis was associated with progressing bone loss. Proresolving activation within 1 wk of stimulus removal and markers of resolving macrophages (IL-10, TGF-β, and CD206) correlated strongly with bone levels. In vivo macrophage depletion with clodronate liposomes prevented bone resorption but impaired regeneration. Induction of resolving macrophages with rosiglitazone, a PPAR-γ agonist, led to reduced bone resorption during inflammatory stimulation and increased bone formation during healing. In vitro assessment of primary bone marrow-derived macrophages activated with either IFN-γ and LPS (proinflammatory activation) or IL-4 (proresolving activation) showed that IL-4-activated cells have enhanced resolving functions (production of anti-inflammatory cytokines; migration and phagocytosis of aged neutrophils) and exert direct anabolic actions on bone cells. Cystatin C secreted by resolving but not inflammatory macrophages explained, in part, the macrophage actions on osteoblasts and osteoclasts. This study supports the concept that therapeutic induction of proresolving functions in macrophages can recouple bone resorption and formation in inflammatory osteolytic diseases.

A75 ROLE OF LRRK2 IN INFLAMMATORY BOWEL DISEASE

Background

Variants of the leucine-rich repeat kinase 2 (LRRK2) are associated with an increased susceptibility to Parkinson disease but also Crohn’s disease (CD).

Aims

The present research is designed to develop a comprehensive understanding of the role of LRRK2 in immune system modulation, and how dysfunction of this pathway may lead to the development of CD.

Methods

WT and LRRK2-deficient neutrophil were infected with Gram-positive Bacteria (Listeria monocytogenes-LM) in a gentamicin protection assays and colony-forming unit assessment will determine the competence of LRRK2 deficient cells for bacterial phagocytosis as well as killing capacity). To examine how LRRK2 is involved in the generation of ROS during the respiratory burst, we will first examine if neutrophil from LRRK2-KO mice have altered ROS generation upon infection with LM and addition of PMA. We evaluate in vitro the ability of neutrophils from LRRK2-KO versus WT mice to transmigrate in vitro in a transwell assay using fMLP as a chemattractant. Also, we investigate the peritoneal cells (by FACS analysis) after injection of different microbial stimuli including FK105 (NOD1 ligand), MDP (NOD2 ligand) and LPS (TLR4 ligand) and anti-cd3 model of ielitis.

Results

We found that LRRK2 KO mice have a defect in migration of neutrophils to the peritoneal cavity after injection of different microbial stimuli including FK10565 (NOD1 ligand), MDP (NOD2 ligand) and LPS (TLR4 ligand). Neutrophils from LRRK2 mice were compromised in their ability to transmigrate in vitro in a transwell assay using fMLP as a chemoattractant. Chemotaxis was also compromised. In parallel, we designed experiments to examine reactive oxygen species (ROS) produced in response to infection of myeloid cells with bacteria. Neutrophils from LRRK2 KO mice infected with Listeria monocytogenes were less able to restrict bacteria growth compared to WT cells. Consistent with these findings, cells from LRRK2 KO mice produced lower levels of ROS following bacterial infection. In order to determine whether myeloid cell migration is compromised in vivo during inflammation, we performed experiments in WT and KO mice looking at different models of ileitis/colitis.

Conclusions

With this work we will further characterize the role of LRRK2 in intestinal homeostasis and mucosal barrier maintenance, including how its deficiency may predispose an individual to developing CD.

Funding Agencies

CAG, CIHR

Oral and Blood Neutrophil Activation States during Experimental Gingivitis

Polymorphonuclear neutrophils (PMNs) are the primary leukocytes present in the healthy and inflamed oral cavity. While unique PMN activation states have been shown to differentiate health and periodontitis, little is known about the changes in PMN activation states that occur during the transition from periodontal health to gingivitis. The objective of this study was to characterize oral and circulatory PMNs during induction and resolution of experimental gingivitis. Healthy volunteers were recruited to undergo experimental gingivitis. Clinical assessment of pocket depths, bleeding on probing, gingival index, and plaque index, as well as flow cytometric analysis of CD (cluster of differentiation) activation markers on blood and oral PMNs, was performed weekly. All clinical parameters increased significantly during the induction period and returned to baseline levels during the resolution phase. During the induction phase, while oral PMN counts increased, oral PMN activation state based on surface expression of CD63, CD11b, CD16, and CD14 was diminished compared to those seen in health and during the resolution phase. PMNs in circulation during onset showed increased activation based on CD55, CD63, CD11b, and CD66a. Using clinical parameters and oral PMN counts assessed at day 21, we noted 2 unique disease patterns where one-third of subjects displayed an exaggerated influx of oral PMNs with severe inflammation compared to the majority of the population who experienced a moderate level of inflammation and PMN influx. This supports the notion that PMN influx and severe inflammatory changes during gingivitis could identify subjects at risk for the development of severe gingival inflammation and progression toward destructive periodontitis. This study demonstrates that oral PMN activation states are reduced in gingivitis and suggest that only in periodontitis do PMNs become hyperactivated and tissue damaging.

Knowledge Transfer Statement: Our article creates a paradigm for future studies of the evolution of essential oral and circulatory biomarkers to identify individuals at risk to develop periodontitis at an early stage of periodontal disease, which is reversible upon proper oral hygiene practices and dental treatments.

The Role of NrF2 in the Regulation of Periodontal Health and Disease

Immune-related disease tolerance is an important defense strategy that facilitates the maintenance of health in organs and tissues that are commonly colonized by bacteria. Immune tolerance to dysbiotic, tooth-borne biofilms is a poorly understood yet clinically relevant concept in the immunopathological mechanisms that are involved in the pathogenesis of periodontitis, particularly those related to neutrophil and macrophage responses. In periodontal health, neutrophils and macrophages respond to the formation of pathogenic bacterial biofilms by the production of bactericidal reactive oxygen species (ROS). However, when released in excess, ROS cause tissue damage and exacerbate inflammation. To counter these destructive responses, many cell types, including neutrophils and macrophages, launch a dedicated antioxidant system that limits the cell and tissue-damaging effects of ROS. The expression of antioxidants is primarily regulated by genetic response elements in their promoters. Here we consider the roles of nuclear factor erythroid 2-related factor (NrF2), a transcription factor, and other key regulators of antioxidants. The concept of disease tolerance, neutrophil and macrophage-generated oxidative stress, and their relationship to the pathogenesis of periodontitis is reviewed. We focus on the regulation of NrF2 and recent evidence suggesting that NrF2 plays a central role in host protection against tissue destruction in periodontitis.

Heterogeneity of osteoclast activity and bone turnover in different skeletal sites

OBJECTIVE

To compare osteoclasts and bone turnover in the cranial and appendicular skeletons of mice and determine whether estrogen depletion has an impact on these differences.

DESIGN

In vitro osteoclastogenesis (OCG) was performed on osteoclasts precursors derived from calvarial, mandibular and femoral bone marrow. In vitro, mature osteoclasts were stained with TRAP in plastic petri dishes and with DAPI and Phalloidin on glass coverslips to identify mature osteoclasts and compare osteoclast surface area and nuclei number in the different bone sites, respectively. Quantification of osteoclast resorption pit (Rpit) volume and surface area from different bone sites was achieved using dentin slices stained with Picrosirius red and confocal microscopy. In vivo TRAP, static and dynamic histomorphometric analyses were performed on 5-month-old mouse calvarial, long bone and mandibular trabecular bone to compare bone resorption and formation rates, respectively. Mice were ovariectomized (OVX) at 5 months of age and sacrificed at 6 months of age to establish an osteoporosis model for differences in osteoclasts activity and to monitor the changes in bone turnover rates in the three bone sites upon estrogen depletion.

RESULT

s Phalloidin stained calvarial osteoclasts were larger compared to long bone and mandibular osteoclasts. Rpits from osteoclasts derived from mandibular bone were smaller and had lower volume values compared to long bone and calvarial bone Rpits. In vivo analysis showed significant increases in bone formation rates in calvarial trabecular bone compared to long bone and mandibular trabecular bone. Turnover was enhanced upon estrogen depletion in calvarial trabecular bone. Resorption was increased without a corresponding increase in bone formation in the trabecular metaphysis of long bone. Mandibular trabecular bones do not appear to be affected by OVX.

CONCLUSION

The cranial and appendicular skeletons differ from one another in that osteoclasts from calvarial bone have the highest resorptive capacity which is coupled to bone formation both pre and post-OVX. Mandibular bones show the lowest turnover rates and are not affected by OVX.

Distinct Oral Neutrophil Subsets Define Health and Periodontal Disease States

Neutrophils exit the vasculature and swarm to sites of inflammation and infection. However, these cells are abundant in the healthy, inflammation-free human oral environment, suggesting a unique immune surveillance role within the periodontium. We hypothesize that neutrophils in the healthy oral cavity occur in an intermediary parainflammatory state that allows them to interact with and contain the oral microflora without eliciting a marked inflammatory response. Based on a high-throughput screen of neutrophil CD (cluster of differentiation) marker expression and a thorough literature review, we developed multicolor flow cytometry panels to determine the surface marker signatures of oral neutrophil subsets in periodontal health and disease. We define here 3 distinct neutrophil subsets: resting/naive circulatory neutrophils, parainflammatory neutrophils found in the healthy oral cavity, and proinflammatory neutrophils found in the oral cavity during chronic periodontal disease. Furthermore, parainflammatory neutrophils manifest as 2 distinct subpopulations-based on size, granularity, and expression of specific CD markers-and exhibit intermediate levels of activation as compared with the proinflammatory oral neutrophils. These intermediately activated parainflammatory populations occur in equal proportions in the healthy oral cavity, with a shift to one highly activated proinflammatory neutrophil population in chronic periodontal disease. This work is the first to identify and characterize oral parainflammatory neutrophils that interact with commensal biofilms without inducing an inflammatory response, thereby demonstrating that not all neutrophils trafficking through periodontal tissues are fully activated. In addition to establishing possible diagnostic and treatment monitoring biomarkers, this oral neutrophil phenotype model builds on existing literature suggesting that the healthy periodontium may be in a parainflammatory state.

Factors Influencing Adoption of New Technologies into Dental Practice: A Qualitative Study

The objective of this study was to explore factors affecting decisions to adopt new technologies into dental practice using a colorimetric rinse test for detection of periodontal disease as a model. Focus groups with key informants in Canadian dentistry and dental hygiene were conducted. A deductive approach used Rogers's diffusion of innovation theory as a framework for organizing codes and subcodes. Two members of the research team independently reviewed and analyzed the data using NVivo 10. The attributes of the technology itself emerged as primary influencers. Perceived relative advantages of the diagnostic mouth rinse over existing methods were potential time efficiency, low implementation cost, and utility of the tool. Low complexity, compatibility with existing routines/beliefs, and the potential for reinvention-the use of a technology for other than its intended purpose (i.e., patient education, monitoring of disease, screening tool in nondental settings)-were other important features enhancing adoption. An overarching concern was that any new technology benefit the patient. Contextual factors also play a role. Numerous communication channels, including opinion leaders, patients, marketing, continuing education courses, and strength of evidence, influenced clinicians, with peer interaction being a stronger influence than marketing. Similar themes arose from specialist, general dentist, and dental hygienist focus groups. Adopter characteristics also came into play: participants ranged in their self-reported innovativeness with many considering themselves "early adopters" of new technology. Findings of this study suggest that the innovation adoption process is not straightforward, but attributes of the innovation, contextual factors, and adopter characteristics play important roles in the process. Knowledge Transfer Statement: Various factors affect the adoption of new tools into clinical dental practice. These include attributes of the test or tool itself, the context of the settings in which the tool is introduced to practitioners, and the characteristics of the clinicians themselves. A qualitative study of dentists and dental hygienists investigated these factors. Situations in which dentists and hygienists interact with their peers and colleagues-through social networks, continuing education courses, conventions, or personal contact-were a major driver in the decision to adopt new technologies. However, even among "early adopters," most were reluctant to use new tests or tools unless they perceived a benefit to their patients or practice.

Deletion of filamin A in monocytes protects cortical and trabecular bone from post-menopausal changes in bone microarchitecture

The objective of the study was to determine the in vivo role of Filamin A (FLNA) in osteoclast generation and function, through the assessment of trabecular bone morphology, bone turnover, and the resulting changes in mechanical properties of the skeleton in mice with targeted deletion of FLNA in pre-osteoclasts. Using a conditional targeted knockdown of FLNA in osteoclasts, we assessed bone characteristics in vivo including micro-computed tomography (micro-ct), histomorphometric analyses, and bone mechanical properties. These parameters were assessed in female mice at 5 months of age, in an aging protocol (comparing 5-month-old and 11-month-old mice) and an osteoporosis protocol [ovariectomized (OVX) at 5 months of age and then sacrificed at 6 and 11 months of age]. In vivo bone densitometry, mechanical and histomorphometric analyses revealed a mild osteoporotic phenotype in the FLNA-null 5-month and aging groups. The WT and FLNA-KO bones did not appear to age differently. However, the volumetric bone mineral density decrease associated with OVX in WT is absent in FLNA-KO-OVX groups. The skeleton in the FLNA-KO-OVX group does not differ from the FLNA-KO group both in mechanical and structural properties as shown by mechanical testing of femora and vertebrae and histomorphometry of vertebrae. Additionally, FLNA-KO femora are tougher and more ductile than WT femora. The result of this study indicates that while FLNA-KO bones are weaker than WT bones, they do not age differently and are protected from estrogen-mediated post-menopausal osteoporosis.

Identification of quantitative trait loci influencing inflammation-mediated alveolar bone loss: insights into polygenic inheritance of host-biofilm disequilibria in periodontitis

BACKGROUND AND OBJECTIVE

The relative contribution of genetic and environmental factors to the onset and progression of periodontitis is inconclusive. Despite the high prevalence, phenotypic heterogeneity and significant local and systemic implications of this disease, early detection and individualized therapy are problematic. Using a murine model of periodontitis in a panel of 17 recombinant inbred mice, the current study addressed the heritability of, and oral dysbiosis associated with, inflammation-mediated alveolar bone loss (iABL), the hallmark of periodontitis.

MATERIAL AND METHODS

Quantitative trait locus (QTL) genomics and quantitative PCR for over 99% of known murine oral microbiota were used.

RESULTS

It was found that iABL is a polygenic trait with 32.7% heritability. One suggestive QTL, nicknamed inflammation-mediated alveolar bone loss locus (iABLL), was identified on chromosome 2. Eleven genes involved in innate immune responses and bone metabolism, particularly related to macrophage and osteoblast function, namely Etl4, Pdss1, Cobll1, 9330158F14Rik, Xirp2, Stk39, Mettl5, Metapl1, Itga6, Pdk1 and Sp3, were found in the iABLL using cis expression QTL and nonsynonymous single nucleotide polymorphism analyses. Specific oral microbiome shifts in saliva and tongue mucosa are associated with disease in this model.

CONCLUSION

Our results indicate that complex host-biofilm interactions generate pathogenic states that extend beyond subgingival biofilms and periodontal tissues. Although no temporal relationship between the onset of iABL and microbiome changes were established, our findings suggest that host factors may be responsible for pathogenic shifts in subgingival biofilms when persistent and undisturbed.

Quantifying oral inflammatory load: oral neutrophil counts in periodontal health and disease

BACKGROUND AND OBJECTIVE

Neutrophils are the primary white blood cells that are recruited to fight the initial phases of microbial infections. While healthy norms have been determined for circulating blood neutrophil counts in order to identify patients with suspected systemic infections, the levels of oral neutrophils (oPMNs) in oral health and in the presence of periodontal diseases have not been described. It is important to address this deficiency in our knowledge as neutrophils are the primary immune cell present in the crevicular fluid and oral environment and previous work has suggested that they may be good indicators of overall oral inflammation and periodontal disease severity. The objective of this study was to measure oPMN counts obtained in a standardized oral rinse from healthy patients and from those with chronic periodontal disease in order to determine if oPMN levels have clinical relevance as markers of periodontal inflammation. A parallel goal of this investigation was to introduce the concept of 'oral inflammatory load', which constitutes the inflammatory burden experienced by the body as a consequence of oral inflammatory disease.

MATERIAL AND METHODS

Periodontal examinations of patients with a healthy periodontium and chronic periodontal disease were performed (n = 124). Two standardized consecutive saline rinses of 30 s each were collected before patient examination and instrumentation. Neutrophils were quantified in the rinse samples and correlated with the clinical parameters and periodontal diagnosis.

RESULTS

Average oPMN counts were determined for healthy patients and for those with mild, moderate and severe chronic periodontal diseases. A statistically significant correlation was found between oPMN counts and deep periodontal probing, sites with bleeding on probing and overall severity of periodontal disease.

CONCLUSIONS

oPMN counts obtained through a 30-s oral rinse are a good marker of oral inflammatory load and correlate with measures of periodontal disease severity.

Zoledronate and pamidronate depress neutrophil functions and survival in mice

BACKGROUND AND PURPOSE

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) has been identified as a severe complication of patients previously treated with i.v. bisphosphonates. It has been noted that necrotic bone from BRONJ sites display signs of bacterial infection suggesting that an immune defect may play a role in the pathophysiology of BRONJ. Here, we have examined the effect of two potent bisphosphonates, zoledronate and pamidronate, on neutrophil function, differentiation and survival.

EXPERIMENTAL APPROACH

The effect of bisphosphonates on chemotaxis, NADPH oxidase activity and neutrophil survival were assessed in vitro using bone marrow-derived primary neutrophils or in vitro differentiated haematopoetic progenitors from mice. The same parameters and the number of circulating neutrophils were quantified in neutrophils isolated from mice treated in vivo with zoledronate. In vivo recruitment of neutrophils was assessed by sodium periodate-induced peritonitis.

KEY RESULTS

Zoledronate and pamidronate inhibited in vitro neutrophil chemotaxis and NADPH oxidase activity in a dose-dependent manner. In vivo recruitment of neutrophils was also suppressed. Zoledronate did not affect in vitro differentiation of neutrophils but shortened their life span in a granulocyte-colony stimulating factor-dependent manner. fMLP-induced activation of RhoA activity was decreased by zoledronate treatment.

CONCLUSIONS AND IMPLICATIONS

Our results show that bisphosphonate exposure leads to impaired neutrophil chemotaxis, neutrophil NADPH oxidase activity and reduced circulating neutrophil counts. This work suggests that bisphosphonates have the potential to depress the innate immune system for a prolonged time, possibly contributing to the pathogenesis of BRONJ.

Deleting Rac1 improves vertebral bone quality and resistance to fracture in a murine ovariectomy model

SUMMARY

The roles of Rac1 and Rac2 in regulating osteoclast-mediated bone quality in postmenopausal osteoporosis were evaluated using an ovariectomized murine model. Animals' bone composition and architecture were evaluated. Our results demonstrate that the deletion of Rac1 increases vertebral bone quality compared to wild-type bones in an ovariectomized model.

INTRODUCTION

To determine the roles of the Rho family small GTPases Rac1 and Rac2 in regulating osteoclast-mediated bone quality in a model of postmenopausal osteoporosis.

METHODS

Twelve-month-old female mice from three genotypes-wild type (WT), Rac1 null (LysM.Rac1 KO), and Rac2 null (Rac2KO)--were studied in control and ovariectomized groups (mice previously ovariectomized at 4 months of age). Animals were sacrificed at 12 months of age, and the femora and vertebrae were harvested for mechanical testing, bone densitometry, micro-computed tomography, and histomorphometric analyses to evaluate bone mineralization and architecture. The results were compared between groups using ANOVA and LSD post-hoc tests.

RESULTS

We observed that LysM.Rac1 KO mice showed higher vertebral bone mineral density compared to WT in both control and ovariectomized groups. Consistent with this finding, LysM.Rac1 KO vertebrae showed increased resistance to fracture and increased trabecular connectivity compared to WT in both groups. Micro-CT analysis revealed that Rac2KO ovariectomized vertebrae have more trabecular bone compared to WT and LysM.Rac1 KO, but this did not translate into increased fracture resistance.

CONCLUSION

Our results demonstrate that the deletion of Rac1 increases vertebral bone quality compared to WT bones in a postmenopausal osteoporosis model.

Novel rinse assay for the quantification of oral neutrophils and the monitoring of chronic periodontal disease

BACKGROUND AND OBJECTIVES

The aim of this study was to develop a single, rapid, noninvasive oral rinse assay to enable the accurate quantification of oral neutrophils. Products released by neutrophils are partly responsible for the destruction observed in periodontitis. Quantification of oral neutrophil levels is important for understanding their role in periodontal diseases. Previous studies have relied on time-consuming serial rinses and cumbersome counting techniques for the collection and quantification of oral neutrophils.

MATERIAL AND METHODS

Patients with chronic periodontal disease provided rinse samples before and after phase I periodontal treatment. Cells in the rinse samples were stained with acridine orange, and neutrophil counts were carried out using a fluorescence microscope and a hemocytometer.

RESULTS

This assay allowed us to detect a significant difference in pretreatment oral neutrophil counts between periodontal disease and healthy control groups (p < 0.001). Patients who responded favorably to phase I therapy demonstrated a 43% reduction in oral neutrophil counts compared with their pretreatment levels (p = 0.019). Patients who did not respond to phase I periodontal treatment showed no significant difference in oral neutrophil levels (p = 0.39).

CONCLUSION

Oral neutrophil levels, as determined by a rapid oral rinse, reflect the severity of periodontal disease and treatment response. A single, rapid, oral rinse assay is an effective means of collecting and quantifying oral neutrophil levels and may serve as an excellent research tool for further study of the role of neutrophils in periodontal diseases.

A noninvasive oral rinse assay to monitor engraftment, neutrophil tissue delivery and susceptibility to infection following HSCT in pediatric patients

The time interval between neutrophil tissue delivery and blood confirmed engraftment following hematopoietic stem cell transplantation (HSCT) may serve as an indicator of patient susceptibility to infection. Using an oral rinse protocol, we studied neutrophil tissue delivery kinetics and its relationship to clinical parameters post-HSCT in 29 pediatric patients. Oral neutrophil counts were compared to circulating neutrophil levels, oral mucositis scores and infection-related febrile episodes after engraftment. Blood engraftment (BE) is currently defined by a blood neutrophil count of > or =0.5 x 10(9)/l. We defined oral engraftment (OE) as the day neutrophils returned in the mouth post-HSCT (> or =0.25 x 10(4)/ml oral neutrophils in the rinse sample). We found that neutrophils reappeared 6.3+/-3.9 s.d. days earlier in the mouth than in the circulation enabling us to identify successful engraftment almost 1 week sooner than using blood count values alone. Furthermore, the time-span between OE and BE was inversely related to the number of infection-related febrile episodes post-BE. We conclude that monitoring the timing of neutrophil tissue delivery through a rapid oral rinse may yield important insights into the biology of neutrophil recovery during and after engraftment and the factors associated with neutrophil tissue recruitment.

Scaling the microrheology of living cells

We report a scaling law that governs both the elastic and frictional properties of a wide variety of living cell types, over a wide range of time scales and under a variety of biological interventions. This scaling identifies these cells as soft glassy materials existing close to a glass transition, and implies that cytoskeletal proteins may regulate cell mechanical properties mainly by modulating the effective noise temperature of the matrix. The practical implications are that the effective noise temperature is an easily quantified measure of the ability of the cytoskeleton to deform, flow, and reorganize.

Endocytic protein intersectin-l regulates actin assembly via Cdc42 and N-WASP

Intersectin-s is a modular scaffolding protein regulating the formation of clathrin-coated vesicles. In addition to the Eps15 homology (EH) and Src homology 3 (SH3) domains of intersectin-s, the neuronal variant (intersectin-l) also has Dbl homology (DH), pleckstrin homology (PH) and C2 domains. We now show that intersectin-l functions through its DH domain as a guanine nucleotide exchange factor (GEF) for Cdc42. In cultured cells, expression of DH-domain-containing constructs cause actin rearrangements specific for Cdc42 activation. Moreover, in vivo studies reveal that stimulation of Cdc42 by intersectin-l accelerates actin assembly via N-WASP and the Arp2/3 complex. N-WASP binds directly to intersectin-l and upregulates its GEF activity, thereby generating GTP-bound Cdc42, a critical activator of N-WASP. These studies reveal a role for intersectin-l in a novel mechanism of N-WASP activation and in regulation of the actin cytoskeleton.

Two pathways through Cdc42 couple the N-formyl receptor to actin nucleation in permeabilized human neutrophils

We developed a permeabilization method that retains coupling between N-formyl-methionyl-leucyl-phenylalanine tripeptide (FMLP) receptor stimulation, shape changes, and barbed-end actin nucleation in human neutrophils. Using GTP analogues, phosphoinositides, a phosphoinositide-binding peptide, constitutively active or inactive Rho GTPase mutants, and activating or inhibitory peptides derived from neural Wiskott-Aldrich syndrome family proteins (N-WASP), we identified signaling pathways leading from the FMLP receptor to actin nucleation that require Cdc42, but then diverge. One branch traverses the actin nucleation pathway involving N-WASP and the Arp2/3 complex, whereas the other operates through active Rac to promote actin nucleation. Both pathways depend on phosphoinositide expression. Since maximal inhibition of the Arp2/3 pathway leaves an N17Rac inhibitable alternate pathway intact, we conclude that this alternate involves phosphoinositide-mediated uncapping of actin filament barbed ends.

Intracellular osteopontin is an integral component of the CD44-ERM complex involved in cell migration

Osteopontin (OPN) is a secreted glycoprotein with mineral- and cell-binding properties that can regulate cell activities through integrin receptors. Previously, we identified an intracellular form of osteopontin with a perimembranous distribution in migrating fetal fibroblasts (Zohar et al., J Cell Physiol 170:88-98, 1997). Since OPN and CD44 expression are increased in migrating cells, we analyzed the relationship of these proteins with immunofluorescence and confocal microscopy. A distinct co-localization of perimembranous OPN and cell-surface CD44 was observed in fetal fibroblasts, periodontal ligament cells, activated macrophages, and metastatic breast cancer cells. The co-localization of OPN and CD44 was prominent at the leading edge of migrating fibroblasts, where OPN also co-localized with the ezrin/radixin/moesin (ERM) protein ezrin, as well as in cell processes and at attachment sites of hyaluronan-coated beads. The subcortical location of OPN in these cells was verified by cell-surface biotinylation experiments in which biotinylated CD44 and non-biotinylated OPN were isolated from complexes formed with hyaluronan-coated beads and identified with immunoblotting. That perimembranous OPN represents secreted protein internalized by endocytosis or phagocytosis appeared to be unlikely since exogenous OPN that was added to cell cultures could not be detected inside the cells. A physical association with OPN, CD44, and ERM, but not with vinculin or alpha-actin, was indicated by immunoadsorption and immunoblotting of cell proteins in complexes extracted from hyaluronan-coated beads. The functional significance of OPN in this complex was demonstrated using OPN-/- and CD-/- mouse fibroblasts which displayed impaired migration and a reduced attachment to hyaluronan-coated beads. These studies indicate that OPN exists as an integral component of a hyaluronan-CD44-ERM attachment complex that is involved in the migration of embryonic fibroblasts, activated macrophages, and metastatic cells.

Intracellular osteopontin is an integral component of the CD44-ERM complex involved in cell migration

Osteopontin (OPN) is a secreted glycoprotein with mineral- and cell-binding properties that can regulate cell activities through integrin receptors. Previously, we identified an intracellular form of osteopontin with a perimembranous distribution in migrating fetal fibroblasts (Zohar et al., J Cell Physiol 170:88-98, 1997). Since OPN and CD44 expression are increased in migrating cells, we analyzed the relationship of these proteins with immunofluorescence and confocal microscopy. A distinct co-localization of perimembranous OPN and cell-surface CD44 was observed in fetal fibroblasts, periodontal ligament cells, activated macrophages, and metastatic breast cancer cells. The co-localization of OPN and CD44 was prominent at the leading edge of migrating fibroblasts, where OPN also co-localized with the ezrin/radixin/moesin (ERM) protein ezrin, as well as in cell processes and at attachment sites of hyaluronan-coated beads. The subcortical location of OPN in these cells was verified by cell-surface biotinylation experiments in which biotinylated CD44 and non-biotinylated OPN were isolated from complexes formed with hyaluronan-coated beads and identified with immunoblotting. That perimembranous OPN represents secreted protein internalized by endocytosis or phagocytosis appeared to be unlikely since exogenous OPN that was added to cell cultures could not be detected inside the cells. A physical association with OPN, CD44, and ERM, but not with vinculin or alpha-actin, was indicated by immunoadsorption and immunoblotting of cell proteins in complexes extracted from hyaluronan-coated beads. The functional significance of OPN in this complex was demonstrated using OPN-/- and CD-/- mouse fibroblasts which displayed impaired migration and a reduced attachment to hyaluronan-coated beads. These studies indicate that OPN exists as an integral component of a hyaluronan-CD44-ERM attachment complex that is involved in the migration of embryonic fibroblasts, activated macrophages, and metastatic cells.

Regulation of stretch-activated intracellular calcium transients by actin filaments

Stretch activation of cation-permeable channels may be an important proximal sensory mechanism in mechanotransduction. As actin filaments may mediate cellular responses to changes of the mechanical properties of the substrate and regulate stretch-induced calcium transients, we examined the role of actin filaments and substrate flexibility in modulating the amplitude of stretch-activated intracellular calcium transients. Human gingival fibroblasts were subjected to mechanical stretch through integrins by magnetic force acting on collagen-coated ferric oxide beads. Intracellular calcium concentration was measured in fura-2-loaded cells by ratio fluorimetry. Cytochalasin D-treatment greatly increased (3-fold) the amplitude of stretch-activated calcium transients in well-spread cells grown on glass coverslips while phalloidin, colchicine or taxol exerted no signficant effects, indicating that actin filaments but not microtubules modulate stretch-activated calcium transients. In freshly plated cells with rounded shapes and poorly developed cortical actin filaments, stretch-induced calcium transients were of 3-fold higher amplitude than well-spread cells plated for 6-24 hrs and with well developed actin filaments. Cells plated on soft collagen-polyacrylamide gels showed round morphology but exhibited <50% of the response to stretch of well-spread cells on inflexible gels. Notably, cells on soft gels showed very heavy phalloidin staining for cortical actin filaments compared with cells on more inflexible surfaces which showed only light staining for cortical actin. While cell shape may have some effect on responsiveness to mechanical stretch, the rigidity of the cell membrane mediated by the extensive cortical actin network appears to be a central determinant in the regulation of stretch-induced calcium signals.

Specific inhibition of skeletal alpha-actin gene transcription by applied mechanical forces through integrins and actin

Skeletal alpha-actin (skA), a prominent fetal actin isoform that is re-expressed by adult cardiac myocytes after chronic overload in vivo, provides a model for studying cytoskeletal gene regulation by mechanical forces in vitro. We have determined the mechanisms by which perpendicular applied forces acting through integrins and the actin cytoskeleton regulate the expression of skA. Rat-2 fibroblasts were transiently transfected with plasmids containing 5'-regulatory regions of the skA gene fused to luciferase coding sequences. A constant, perpendicular force (0.2 pN/micrometer(2)) was applied by using a collagen-magnetic bead model; a 25% deformation was obtained on the dorsal cell surface. In this system, force is applied through focal adhesion integrins and strongly induces actin assembly [Glogauer, Arora, Yao, Sokholov, Ferrier and McCulloch (1997) J. Cell Sci. 110, 11-21]. skA promoter activity was inhibited by 68% in cells subjected to 4 h of applied force, whereas Rous sarcoma virus promoter activity was unaffected. In cells transiently transfected with a skA expression vector there was also a parallel 40% decrease in skA protein levels by force, as shown by Western blotting. In L8 cells, constitutive skA expression was decreased by more than 50%. Analyses of specific motifs in the skA promoter revealed that transcriptional enhancer factor 1 and Yin and Yang 1 sites, but not serum response factor and Sp1 sites, mediated inhibitory responses to force. In cells treated with cycloheximide the force-induced inhibition was abrogated, indicating a dependence on new protein synthesis. Inhibition of actin filament assembly with either cytochalasin D or Ca(2+)-depleted medium blocked the inhibitory effect induced by the applied force, suggesting that actin filaments are required for the regulation of skA promoter activity. Western blot analysis showed that p38 kinase, but not Jun N-terminal kinase or extracellular signal-regulated protein kinase 1/2, was activated by force; indeed, the p38 kinase inhibitor SB203580 relieved the force-induced inhibition of skA. We conclude that the force-induced inhibition of skA promoter activity requires an intact actin cytoskeleton and can be mapped to two different response elements. This inhibition might be mediated through the p38 kinase.

Cell-substrate separation: effect of applied force and temperature

We measure the change in cell-substrate separation in response to an upward force by combining two relatively new techniques, Electric Cell-substrate Impedance Sensing (ECIS) to measure average cell-substrate separation, and collagen-coated magnetic beads to apply force to the top (dorsal) surface of cells. The collagen-coated ferric oxide beads attach to integrin receptors in the dorsal surfaces of osteoblastlike ROS 17/2.8 cells. Magnetic force is controlled by the position and the number of permanent magnets, applying an average 320 or 560 pN per cell. Comparing model calculations with experimental impedance data, the junctional resistivity of the cell layer and the average distance between the lower (ventral) cell surface and substrate can be determined. The ECIS analysis shows that these forces produce an increase in the distance between the ventral cell surface and the substrate that is in the range of 10 to 25%. At temperatures of 4 degrees, 22 degrees and 37 degrees C, the measured cell surface-substrate distances without magnetic beads are 84 +/- 4, 45 +/- 2 and 38 +/- 2 nm. The force-induced changes at 22 degrees are 11 +/- 3 and 21 +/- 3 nm for 320 and 560 pN, and at 37 degrees they are 5 +/- 2 and 9 +/- 2 nm. The resulting cell-substrate spring constants at 22 degrees and 37 degrees are thus about 28 and 63 pN nm-1 (dyne cm-1). Using a reasonable range for the number for individual integrin-ligand adhesion bonds gives a range for the spring constant of the individual adhesion bond of from about 10(-3) to 10(-1) pN nm-1. These data also provide evidence that the number of adhesion bonds per cell increases with temperature.

Treponema denticola outer membrane inhibits calcium flux in gingival fibroblasts

Treponema denticola is a cultivable oral spirochete which perturbs the cytoskeleton in cultured cells of oral origin, but intracellular signalling pathways by which it affects actin assembly are largely unknown. As the outer membrane (OM) of Treponema denticola disrupts actin-dependent processes that normally require precise control of intracellular calcium, we studied the effects of an OM extract on internal calcium release, ligand-gated and calcium release-activated calcium channels, and related mechanosensitive cation fluxes in human gingival fibroblasts (HGF). Single-cell ratio fluorimetry demonstrated that in resting cells loaded with Fura-2, baseline intracellular Ca2+ concentration ([Ca2+]i) was not affected by treatment with OM extract, but normal spontaneous [Ca2+]i oscillations were dramatically increased in frequency for 20 to 30 min followed by complete blockade. OM extract inhibited ATP-induced and thapsigargin-induced release of calcium from intracellular stores by 40 and 30%, respectively. Addition of Ca2+ to the extracellular pool following depletion of intracellular Ca2+ by thapsigargin and extracellular Ca2+ by EGTA yielded 59% less replenishment of [Ca2+]i in OM extract-treated than in control HGF. In cells loaded with collagen-coated ferric oxide beads to stimulate integrin-dependent calcium release, baseline [Ca2+]i was nearly doubled but was not significantly different in control and OM extract-treated cells. Magnetically generated tensile forces on the beads induced >300% increases of [Ca2+]i above baseline. Cells preincubated with OM extract exhibited dose-dependent and time-dependent reductions in stretch-induced [Ca2+]i transients, which were due to neither loss of beads from the cells nor cell death. The T. denticola OM inhibitory activity was eliminated by heating the OM extract to 60 degrees C and by boiling but not by phenylmethylsulfonyl fluoride treatment. Thus nonlipopolysaccharide, nonchymotrypsin, heat-sensitive protein(s) in T. denticola OM can evidently inhibit both release of calcium from internal stores and uptake of calcium through the plasma membrane, possibly by interference with calcium release-activated channels.

The role of actin-binding protein 280 in integrin-dependent mechanoprotection

To survive in a mechanically active environment, cells must adapt to variations of applied membrane tension. A collagen-coated magnetic bead model was used to apply forces directly to the actin cytoskeleton through integrin receptors. We demonstrate here that by a calcium-dependent mechanism, human fibroblasts reinforce locally their connection with extracellular adhesion sites by inducing actin assembly and by recruiting actin-binding protein 280 (ABP-280) into cortical adhesion complexes. ABP-280 was phosphorylated on serine residues as a result of force application. This phosphorylation and the force-induced actin reorganization were largely abrogated by inhibitors of protein kinase C. In a human melanoma cell line that does not express ABP-280, actin accumulation could not be induced by force, whereas in stable transfectants expressing ABP-280, force-induced actin accumulation was similar to human fibroblasts. Cortical actin assembly played a role in regulating the activity of stretch-activated, calcium-permeable channels (SAC) since sustained force application desensitized SAC to subsequent force applications, and the decrease in stretch sensitivity was reversed after treatment with cytochalasin D. ABP-280-deficient cells showed a > 90% increase in cell death compared with ABP-280 +ve cells after force application. We conclude that ABP-280 plays an important role in mechanoprotection by reinforcing the membrane cortex and desensitizing SACs.

A new method for application of force to cells via ferric oxide beads

We describe a new method that uses straightforward physics to apply force to substrate-attached cells. In this method, collagen-coated magnetic ferric oxide beads attach to the dorsal surface of cells via receptors of the integrin family, and a magnetic field gradient is applied to produce a force. In this paper we present a complete characterization of the method in a configuration that is easy to use, in which a permanent magnet provides a fairly uniform gradient over a relatively large area. This allows a fairly uniform average force that can be controlled in magnitude, direction, and duration to be applied to a large number of cells. We show how to determine the applied force per cell by measuring the force per unit volume of magnetic bead, the distribution of bead diameters, and the distribution of beads per cell. We also show how to calculate the force per unit volume of bead in a three-dimensional region near the permanent magnet on the basis of field measurements, and present results for three of the magnets. An upward force applied to fibroblasts by this method produces a measurable time-dependent increase in attachment of cytoskeletal actin filaments to the force application points, and an increase in actin cross-linking. This is accompanied by an actin-dependent retraction of the force-induced upward movement of the dorsal surface of the cells.

Calcium ions and tyrosine phosphorylation interact coordinately with actin to regulate cytoprotective responses to stretching

The actin-dependent sensory and response elements of stromal cells that are involved in mechanical signal transduction are poorly understood. To study mechanotransduction we have described previously a collagen-magnetic bead model in which application of well-defined forces to integrins induces an immediate (&lt; 1 second) calcium influx. In this report we used the model to determine the role of calcium ions and tyrosine-phosphorylation in the regulation of force-mediated actin assembly and the resulting change in membrane rigidity. Collagen-beads were bound to cells through the focal adhesion-associated proteins talin, vinculin, alpha 2-integrin and beta-actin, indicating that force application was mediated through cytoskeletal elements. When force (2 N/m2) was applied to collagen beads, confocal microscopy showed a marked vertical extension of the cell which was counteracted by an actin-mediated retraction. Immunoblotting showed that force application induced F-actin accumulation at the bead-membrane complex but vinculin, talin and alpha 2-integrin remained unchanged. Atomic force microscopy showed that membrane rigidity increased 6-fold in the vicinity of beads which had been exposed to force. Force also induced tyrosine phosphorylation of several cytoplasmic proteins including paxillin. The force-induced actin accumulation was blocked in cells loaded with BAPTA/AM or in cells preincubated with genistein, an inhibitor of tyrosine phosphorylation. Repeated force application progressively inhibited the amplitude of force-induced calcium ion flux. As force-induced actin reorganization was dependent on calcium and tyrosine phosphorylation, and as progressive increases of filamentous actin in the submembrane cortex were correlated with increased membrane rigidity and dampened calcium influx, we suggest that cortical actin regulates stretch-activated cation permeable channel activity and provides a desensitization mechanism for cells exposed to repeated long-term mechanical stimuli. The actin response may be cytoprotective since it counteracts the initial force-mediated membrane extension and potentially strengthens cytoskeletal integrity at force-transfer points.

Magnetic fields applied to collagen-coated ferric oxide beads induce stretch-activated Ca2+ flux in fibroblasts

The ability to apply controlled forces to the cell membrane may enable elucidation of the mechanisms and pathways involved in signal transduction in response to applied physical stimuli. We have developed a magnetic particle-electromagnet model that allows the application of controlled forces to the plasma membrane of substrate-attached fibroblasts. The system allows applied forces to be controlled by the magnitude of the magnetic field and by the surface area of cell membrane covered with collagen-coated ferric beads. Analysis by single-cell ratio fluorimetry of fura 2-loaded cells demonstrated large calcium transients (50-300 nM) in response to the magnetic force applications. Experiments using either the stretch-activated channel blocker gadolinium chloride or ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to eliminate external calcium ions, or addition of extracellular manganese ions, indicated that there was a calcium influx through putative stretch-activated channels. The probability of a calcium influx in single cells was increased by higher surface bead loading and the degree of cell spreading. Depolymerization of actin filaments by cytochalasin D increased the amplitude of calcium response twofold. The regulation of calcium flux by filamentous actin content and by cell spreading indicates a possible modulatory role for the cytoskeleton in channel sensitivity. Magnetic force application to beads on single cells provides a controlled model to study mechanisms and heterogeneity in physical force stimulation of cation-permeable channels.

Induced endocytosis in human fibroblasts by electrical fields

Electroporation creates transient pores through which exogenous molecules can gain access to the cell cytoplasm. However, the electrical events associated with this phenomenon may perturb membrane-dependent events such as endocytosis. To measure the effect of electroporation on endocytosis, suspensions of human gingival fibroblasts were subjected to 5-ms electrical discharges, allowed to recover for variable periods of time, incubated with fluorescent probes, and then analyzed by flow cytometry. Incubation of electroporated fibroblasts with FITC-conjugated bovine serum albumin (BSA) to label moities on cell membranes nonspecifically demonstrated a time-dependent increase of internalized probe for up to 90 min after electroporation. Pretreatment incubation of cells with cytochalasin D abrogated the increased internalization of FITC-BSA due to electroporation. Compared to controls, fluorescence signals due to internalization of surface glycoproteins with FITC-concanavalin A were 43% higher after electroporation and treatment with endoglycosidase F or H to reduce probe associated with surface membrane. Confocal microscopy confirmed intracellular labeling and reduction of membrane-associated probe by the enzyme. Assessment of nonspecific FITC-Con A labeling of cells by pretreatment with alpha-methyl D-mannoside showed that labeling was largely (92%) specific. Compared to controls, electroporation induced a 60% increase of internalization of lucifer yellow, a fluid-phase endocytosis marker. Dual fluorescence labeling of membrane phosopholipids by FITC and TRITC-DHPE demonstrated an increased acidification after electroporation that was time dependent, indicating that electroporation induced more rapid entry of membrane lipid into endosomal compartments. These data demonstrate that the electrical fields used in electroporation of fibroblasts cause an actin-dependent increase in the internalization of all membrane components examined and an increased rate of probe entry in to acidifying compartments.

T-cell receptor-gamma delta association with lymphocyte populations in sheep intestinal mucosa

T cells expressing T-cell receptor (TcR)-gamma delta and CD8 represent a significant population in mouse and chicken intra-epithelial lymphocytes (IEL) but represent a minor population in human IEL. We examined the TcR-gamma delta usage and co-expression of CD5, CD4, CD8 and major histocompatibility complex (MHC) class II on isolated sheep IEL and lamina propria lymphocytes (LPL), and compared them with the TcR-gamma delta + cells in peripheral blood, intestinal lymph and jejunal Peyer's patches (PP). There were a number of notable differences. TcR-gamma delta + cells comprised 18% of IEL and 10% of LPL. Among the population of TcR-gamma delta + IEL, 24% were CD8+ and 54% were CD5+, which contrasts with the TcR-gamma delta + cells in blood and intestinal lymph that were universally CD5+ CD4- CD8-. A notable feature of the IEL was the presence of distinct CD8+ and TcR-gamma delta + populations that lacked CD5. Also a high percentage of IEL and LPL were CD2+ and MHC class II+. Analysis of the expression of MHC class II on T-cell subsets, as an indicator of activation, showed that 60-95% of the various IEL and LPL subsets were MHC class II+ compared with only 5-40% in jejunal PP, lymph nodes, spleen and blood. Therefore, it is possible that the circulating TcR-gamma delta + and CD8+ cells that localize in the gut epithelium might become activated and stop the expression of CD5 under the influence of the local microenvironment. These cells appear not to emigrate while still expressing the TcR-gamma delta + (CD8+) CD5- MHC class II+ phenotype. Our data, together with those from other studies, show that there is much heterogeneity in the use of TcR-gamma delta and accessory T-cell molecules by IEL.

Introduction of large molecules into viable fibroblasts by electroporation: optimization of loading and identification of labeled cellular compartments

Access to the cell cytoplasm in viable cells may permit direct labeling or manipulation of intracellular molecules and metabolic processes. One method to gain access to the cell cytoplasm is by electroporation, a technique that transiently creates pores in cell membranes by means of applied electrical fields. We used electroporation to introduce large-molecular-mass dextrans and proteins as probes of the cytoplasmic compartment in human gingival fibroblasts. Electrical field strength and pulse decay time were optimized to obtain cellular viability greater than 80%. Analysis by confocal microscopy and by fluorescence spectrophotometry demonstrated that a large proportion of high-molecular-mass probe was membrane-bound after electroporation. Trypsinization did not affect membrane-bound FITC-dextran but eliminated protein probe incorporated into the membrane, thereby permitting measurement of only intracellular, cytoplasmic label. Proteins of up to 66 kDa were incorporated at intracellular concentrations of 10(-15) M. After electroporation under optimal conditions, incorporated anti-vimentin antibodies were capable of binding to vimentin. Cells electroporated in the presence of RNase A exhibited significant reductions of cellular RNA. Electroporation appears to be a useful approach to probe or perturb specific cellular processes by introduction of functional molecular species into the cytoplasm of viable cells.