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PubMed2000

Mercury mass balances: a case study of two North Dakota power plants.

The Energy & Environmental Research Center (EERC) conducted a mercury-sampling program to provide data on the quantity and forms of Hg emitted and on the Hg removal efficiency of the existing air pollution control devices at two North Dakota power plants--Milton R. Young Station and Coal Creek Station. Minnkota Power Cooperative, Great River Energy, the North Dakota Industrial Commission, and EPRI funded the project. The primary objective was to obtain accurate measurements of Hg released from each plant, as verified by a material balance. A secondary objective was to evaluate the ability of a mercury continuous emission monitor (CEM) to measure total Hg at the stack. At both plants, speciated Hg measurements were made at the inlets and outlets of both the electrostatic precipitators (ESPs) and the flue gas desulfurization (FGD) systems. A Semtech Hg 2000 (Semtech Metallurgy AB) mercury CEM was used to measure the total Hg emissions at the stack in real time. Using these measurements and plant data, the measured Hg concentrations in the coal, FGD slurries, and ESP ash, a Hg mass flow rate was calculated at each sampling location. Excellent Hg mass balances were obtained (+/- 15%). It was also found that the Hg was mostly in the elemental phase (approximately 90%), and the small amount of oxidized Hg that was generated was removed by the FGD systems. Insignificant amounts of particulate-bound Hg were measured at both plants. However, 10-20% of the elemental Hg measured prior to the ESP was converted to oxidized Hg across the ESP. The data show that, at these facilities, almost all of the Hg generated is being emitted into the atmosphere as elemental Hg. Local or regional deposition of the Hg emitted from these plants is not a concern. However, the Hg does become part of the global Hg burden in the atmosphere. Also, the evidence appears to indicate that elemental Hg is more difficult to remove from flue gas than oxidized Hg is.

Air Pollution↗

PubMed1989

Hemofiltration: an alternative to dialysis.

Continuous arteriovenous hemofiltration (CAVH) is a relatively new procedure designed to relieve fluid overload. It has proved useful in many patients whose ability to maintain fluid homeostasis is compromised. Burn victims, patients with acute renal failure, patients with pulmonary edema, and trauma patients have all received benefit from CAVH. CAVH is an extracorporeal circuit in which blood is propelled by the force of the patient's blood pressure through a filter, ultrafiltered, and returned to the patient. CAVH removes fluid and solutes more slowly than hemodialysis, eliminating the danger of rapid fluid and electrolyte shifts. There are several ways to perform the procedure but all require intense and sophisticated medical and nursing care. Strong knowledge of fluid, electrolyte, and acid/base balance, hemodynamics, and assessment skills is required. The ability to intervene quickly and appropriately if trouble arises is a necessity. The dynamics of the treatment are discussed in detail in this article. How to deliver a safe and efficient treatment, troubleshooting guidelines, and suggestions for accurate documentation are also included.

Acute Kidney Injury↗

PubMed2000

A clinical measure of maximal and rapid stepping in older women.

BACKGROUND: In older adults, clinical measures have been used to assess fall risk based on the ability to maintain stance or to complete a functional task. However, in an impending fall situation, a stepping response is often used when strategies to maintain stance are inadequate. We examined how maximal and rapid stepping performance might differ among healthy young, healthy older, and balance-impaired older adults, and how this stepping performance related to other measures of balance and fall risk. METHODS: Young (Y; n = 12; mean age, 21 years), unimpaired older (UO; n = 12; mean age, 69 years), and balance-impaired older women IO; n = 10; mean age, 77 years) were tested in their ability to take a maximal step (Maximum Step Length or MSL) and in their ability to take rapid steps in three directions (front, side, and back), termed the Rapid Step Test (RST). Time to complete the RST and stepping errors occurring during the RST were noted. RESULTS: The IO group, compared with the Y and UO groups, demonstrated significantly poorer balance and higher fall risk, based on performance on tasks such as unipedal stance. Mean MSL was significantly higher (by 16%) in the Y than in the UO group and in the UO (by 30%) than in the IO group. Mean RST time was significantly faster in the Y group versus the UO group (by 24%) and in the UO group versus the IO group (by 15%). Mean RST errors tended to be higher in the UO than in the Y group, but were significantly higher only in the UO versus the IO group. Both MSL and RST time correlated strongly (0.5 to 0.8) with other measures of balance and fall risk including unipedal stance, tandem walk, leg strength, and the Activities-Specific Balance Confidence (ABC) scale. CONCLUSION: We found substantial declines in the ability of both unimpaired and balance-impaired older adults to step maximally and to step rapidly. Stepping performance is closely related to other measures of balance and fall risk and might be considered in future studies as a predictor of falls and fall-related injuries.

Accidental Falls↗

PubMed1991

Effects of full-length and truncated insulin-like growth factor-I on nitrogen balance and muscle protein metabolism in nitrogen-restricted rats.

The ability of insulin-like growth factor-I (IGF-I) to protect against losses of body protein during periods of dietary nitrogen restriction has been evaluated in young rats. Recombinant human IGF-I was administered by osmotic pumps at dose rates of 0, 1.2 or 2.9 mg/kg per day over a 7-day period beginning with the transfer of animals from an 18% to a 4% protein diet. A fourth group received the potent truncated IGF-I analogue, des(1-3)IGF-I, at a dose of 1.2 mg/kg per day over a comparable 7-day period. Plasma IGF-I levels were reduced by 60% following nitrogen restriction, a reduction that was partly prevented by IGF-I administration, especially at the higher dose, but not measurably by des(1-3)IGF-I. The major IGF-binding protein circulating in blood, IGFBP-3, demonstrated a similar pattern of change. A significant (P less than 0.05) protection of body weight was achieved in the low dose IGF-I and des(1-3)IGF-I groups, but only after differences in food intake had been eliminated by analysis of covariance. Nitrogen balances were not significantly different unless analysis of covariance was used to adjust for the nitrogen intakes, whereupon all treatment groups showed improved balance, especially the animals treated with the low IGF-I dose and des(1-3)IGF-I (both P less than 0.01). The rate of muscle protein breakdown calculated from the urinary excretion of 3-methyl-histidine was not significantly altered by the treatments, but fell progressively throughout the 7 days. The fractional rate of muscle protein synthesis measured on the final day was increased by 31,26 and 21% respectively by the low and high doses of IGF-I and by des(1-3)IGF-I. Organ weights (g/kg body weight) showed no effects of IGF-I treatment except for 16% increases in the weight of kidneys in the high dose IGF-I and the des(1-3)IGF-I groups. Carcass analyses demonstrated higher water and lower fat contents (all P less than 0.01) in the same groups. These results suggest that exogenous IGF-I and especially des(1-3)IGF-I can partly protect body protein reserves during nitrogen restriction.

Animals↗

PubMed2001

Standardizing digital photography: it's not all in the eye of the beholder.

Advances in digital photography have made it an efficient and economically appealing alternative to conventional photography. Nevertheless, as objective observers and clinical photographers, we must realize that all digital cameras are not created equal. Different digital cameras frequently used in plastic surgery practices (Olympus 600DL, Olympus 2500, Sony DSC-D700, Nikon Coolpix 950, and Nikon D1) were evaluated, using a subject photographed with each camera in the identical lighting conditions, to determine inherent differences in quality, color, and contrast of the resultant photographs. Three different lighting conditions were examined: single soft-box lighting, dual studio flash boxes, and operating room lighting with on-camera flash. The same digital settings (program mode, ISO camera default setting, high quality setting with JPEG compression) were used. Each camera was digitally color balanced using an 18 percent gray card. Raw and color-balanced images were viewed side-by-side. The macro-image capabilities of each camera were also examined. Conventional 35-mm photographs using a 105 macro-lens on Kodachrome and Ektachrome slide film were obtained for comparison. All of the digital cameras performed with noticeable differences, but they maintained consistency in the three different lighting conditions. Digital photographs differed most greatly with respect to quality and contrast, which was especially obvious once color balancing was performed. Marked differences in quality and ability were observed with respect to macro-image capabilities. Inherent differences in features among digital cameras produce dramatically different photographic results with regard to color, contrast, focus, and overall quality. With the increasing use of digital photography in plastic surgery journals and presentations, it must be recognized that digital cameras do not all display photographs of similar quality, especially when used to evaluate skin appearance. To standardize digital photography, the surgeon must realize that switching digital cameras is akin to switching film types. Standardization of digital photographs should include image resolution between 1.5 and 2.7 million pixels, ISO default setting, color balancing with an 18 percent gray card and software, consistency in focal distance, JPEG compression of medium-to-high quality, and backgrounds of medium blue or 18 percent gray.

Female↗

PubMedDate not supplied

ELGAM--extra-laboratory gait assessment method: identification of risk factors for falls among the elderly at home.

Gait and balance disturbances are recognized risk factors for falls among elderly persons. The prevention of falls and their adverse complications is one of the challenges in geriatric care, requiring the early detection of risk factors. Heretofore, gait assessment procedures have required considerable investment in equipment for sophisticated biomechanical testing. This has limited the use of gait-testing procedures to the laboratory or clinic. We describe a simple and effective method for at-home or community gait testing, ELGAM (extra-laboratory gait assessment method). ELGAM was field-tested as part of a study of 36 community-dwelling elderly in Beer Sheba, Israel. The ELGAM parameters studied included step length, walking speed, initial starting style of walking, ability to turn head while walking, and static balance. Slow walking speed (less than 0.5 m/s), small steps, difficulty in turning the head, and impaired balance were significantly associated (chi-square analyses, p less than 0.01) with unstable gait. The parameters were also positively associated one with another, except for head turning. The ELGAM parameters were significantly related to self-assessed fall frequency, and reported 'near falls' among women only. In addition, among women only, slow walking speed was associated with depressive symptoms as detected by a validated screening test, the Short Geriatric Depression Scale, and with poor subjective health rating. Among 58% of this independently living elderly sample, ELGAM detected one or more risk factors. ELGAM is a 'low-tech', functionally based, effective method for direct recording of gait parameters that is applicable for community studies of the early detection of risk factors for falls and mobility problems.

Accidental Falls↗

PubMed2000

Chair configuration and balance control in persons with spinal cord injury.

OBJECTIVE: To study whether chair configuration influences sitting balance in persons with spinal cord injury (SCI). DESIGN: Cross-sectional group study. SETTING: Rehabilitation centers and hospital rehabilitation departments. PATIENTS: Ten complete high thoracic SCI (level T2-T8) patients, 10 complete low thoracic SCI (T9-T12) patients, and 10 matched able-bodied controls. SCI participants had completed their active rehabilitation at least 6 months before the study. INTERVENTIONS: A balance-changing (forward) reaching task while seated in four differently configured chairs. Tilt angle (7 degrees and 12 degrees) and reclination angle (22 degrees) were varied relative to a standard chair configuration (10 degrees reclination). MAIN OUTCOME MEASURES: Maximal unsupported reaching distance, center-of-pressure displacement and muscle activity. RESULTS: Although no significant difference in actively controllable reach was found in controls or in subjects with low SCI, sitting balance improved in all chairs relative to the standard chair. Ability to control displacement of arms and trunk during reaching improved. No apparent need for additional postural muscle activity was found. Persons with high SCI did not improve their sitting balance. They were unable to control a shift in body mass larger than the one induced by arm movement. However, they had less muscle activity after backrest reclination or tilting the chair backwards. CONCLUSIONS: The tested chairs had an overall positive effect. However, for individually tailored chair configurations factors other than those investigated should be considered.

Adult↗

PubMed1990

Rehabilitation of chronic stroke patients: changes in functional performance.

Forty stroke patients who were at least one year post-onset completed a one-month intensive rehabilitation program. The month before the program served as a control period. During the program, patients received individual sessions in occupational and physical therapy four days a week, and they participated in group activities on the fifth day. Therapy emphasized instruction in motor planning, balance and weight shift, and the use of adaptive equipment; these motor abilities were then practiced within real life situations. The patients demonstrated significant improvement in the outcome measures of weight shift, balance, and ADL scores after the one-month rehabilitation program (weight shift: F = 16.1, p = .0001; balance: F = 6.26, p = .0007; ADL: F = 13.8, p = .0001). They retained these new skills during a three-month follow-up period.

Activities of Daily Living↗

PubMed1985

Lecithin:cholesterol acyltransferase regulation. II. Effect of fluidity of egg phosphatidylcholine vesicles.

The regulation of human plasma lecithin:cholesterol acyltransferase (LCAT) by changes in bilayer fluidity of substrate egg phosphatidylcholine (egg PC) unilamellar vesicles was investigated using pyrene excimer fluorescence to measure fluidity. Fluidity was decreased by adding up to 20% cholesterol or increased by adding up to 10% egg 2-lysophosphatidylcholine (lysoPC). The fluidizing effect of lysoPC was suppressed by the addition of cholesterol. LCAT activity with 10% cholesterol vesicles was decreased by adding 5% lysoPC, yet activity with 5% cholesterol vesicles was unaffected by adding 5% lysoPC. This difference may be explained by a balance between the known LCAT inhibitory effect of lysoPC and its ability to increase bilayer fluidity and thereby increase LCAT activity. LCAT esterification of up to 37% of vesicle cholesterol failed to alter the lysoPC/cholesterol balance sufficiently to influence activity in this system. The findings of our studies are in keeping with modulation of LCAT activity by bilayer fluidity, but fluidity changes caused by enzyme action are not sufficient to regulate that activity.

Egg Yolk↗

PubMed2004

Age-related reduction in sagittal plane center of mass motion during obstacle crossing.

Accidental falls are a leading cause of injury and death in the growing elderly population. Traumatic falls are frequent, costly, and debilitating. Control of balance during locomotion is critical for safe ambulation, but relatively little is known about the natural effect of aging on dynamic balance control. Samples of healthy young (n = 13) and elderly (n = 13) subjects were compared in the interactive measures of center of mass (COM) and center of pressure (COP) during level walking and obstacle crossing conditions. Obstacle heights were normalized to individual body height (2.5%, 5%, 10%, and 15%). Temporal-distance (T-D) variables of gait were also compared. Statistical analyses were conducted using a two-way ANOVA for subject group and obstacle height. T-D parameters were not significantly different between groups; nor were frontal plane COM and COP parameters. Significant age differences did exist for antero-posterior (A/P) motion of the COM (decreased motion in the elderly), and its relationship with the COP (reduced separation between the two variables in the elderly). Anterior COM velocities were also significantly lower in the elderly group. The results confirm the ability of healthy elderly adults to maintain dynamic balance control in the frontal plane during locomotion. Reduced A/P distances between the COM and COP indicate a conservative reduction of the mechanical load on joints of the supporting limb. This conservative strategy may be related to a reduction in muscle strength as it occurs in the natural aging process.

Accidental Falls↗

PubMedDate not supplied

Anatomical and physiologic characteristics to predict football ability. Report of study methods and correlations, University of Arkansas, 1976.

In a prospective study of 56 scholarship players at the University of Arkansas in 1976, 14 anatomical and physiologic measurements were carried out on each of the 56 players, to include certain orthopaedic strength, power, and balance tests, and compared to the coaches' subjective ratings of football ability in an effort to determine which characteristics best correlate to the athlete's true performance. The correlation matrix for the criterion measure and the predictor variables of selected anatomical strength, balance, and power measures are presented, and the results of the study indicate that genu varum (0.445) and tibial torsion (-0.33) had the highest correlation with the coaching criterion variable. The average tibial torsion was 42.6 for these scholarship athletes, while normal average tibial torsion among a nonscholarship group was 27.40 degrees. Other anatomical characteristics measured, as well as strength and power measure, could not reach the critical level of +/- 0.263 to be significant at the 0.05 level, although horsepower was close (0.255). The Margaria-Kalamen power test was significantly related to the 40-yard dash, and a moderately good measure of football ability.

Anthropometry↗

PubMed1991

Modulation of concanavalin A-induced, antigen-nonspecific regulatory cell activity by leu-enkephalin and related peptides.

We have developed a system in which human peripheral blood mononuclear cells (PBMC) stimulated with concanavalin A (Con A) can be examined for regulatory cell activity upon coculture with responder cells undergoing mitogenic proliferation. Low concentrations of Con A resulted in the induction of helper function, while higher concentrations of Con A induced suppressor activity in the PBMC population. However, for each individual donor a particular concentration of Con A can be found at which point no regulatory cell activity is observed. This "balance point" provides a set of conditions under which the ability of an immunomodulator to up-regulate or down-regulate the system can be studied. The ability of leu-enkephalin to positively or negatively regulate an immune response was examined under these circumstances. The addition of leu-enkephalin to cultures stimulated by Con A at this balance point enhanced both suppressor cell (Ts) and helper cell (Th) activity in a concentration-dependent manner. The induction of Ts activity displayed a bimodal response at concentrations between 10(-12) to 10(-13) M and 10(-9) to 10(-10) M, while the induction of Th activity was consistently observed at 10(-11) M. Similar effects were seen with either of the peptides Tyr-Gly and Tyr-Gly-Gly, corresponding to the first two and three amino acids of the N-terminal ends of the enkephalins. Th activity was consistently enhanced at 10(-13) M Tyr-Gly-Gly and 10(-14) M Tyr-Gly. This suggests that leu-enkephalin may either positively or negatively regulate immune responses and that the intact leu-enkephalin molecule is not required for these effects.

Concanavalin A↗

PubMed2006

Reaching upward is more challenging to dynamic balance than reaching forward.

BACKGROUND: Older adults have less confidence in their ability to reach upward compared to reaching forward. The forward reach test may, therefore, not be ideally suited for detecting functional deficits that directly affect daily activities. METHODS: A new test of upward reach and forward reach (along a 50-degree track) were administered to young and older adults. Reach distance was adjusted for foot length and normalized to stature. The anterior safety margin was calculated by relating the center of pressure to the base of support. The extent to which age, sex, balance confidence, anthropometric, and center of pressure parameters contribute to forward and upward reach performance was assessed. FINDINGS: Reach and anterior safety margin scores were well-correlated between forward and upward reaching, but the upward reach test posed a greater challenge to dynamic balance - eliciting a smaller anterior safety margin from both older and younger subjects. Further, compared to young adults, older adults showed greater limitations in reach distance and balance parameters during upward reach compared with forward reach. An observational measure of reach strategy (whether or not the heels were raised from the platform during the test) differentiated between higher and lower reach performance for older adults. Anthropometric variables accounted for much of the variance in reach performance that would otherwise have been attributed to an age-related loss of functional capacity. Balance confidence scores also contributed to regression models predicting upward - but not forward - reach performance in older adults. INTERPRETATION: Though upward and forward reach performances were well related in this sample, a test of upward reach may be better suited to reveal early signs of functional decline in older adults than a test of forward reach.

Adult↗

PubMed1999

Self-efficacy beliefs and perceived declines in functional ability: MacArthur studies of successful aging.

Longitudinal data from a cohort of older men and women, aged 70-79, were used to test the hypothesis that stronger self-efficacy beliefs would protect against onset of perceived functional disabilities over a 2.5-year follow-up, independent of underlying physical ability. Standard self-report scales were used to assess perceived functional disabilities, ranging from mild performance difficulties (measured by a 5-item scale based on items by Nagi) to more severe disabilities (measured by the 7-item Katz Activities of Daily Living Scale [ADL]). Performance-based measurements of strength, balance, and gait provide more objective assessments of physical abilities. Self-efficacy beliefs were measured in terms of beliefs relating to managing interpersonal relationships and beliefs relating to managing more instrumental daily activities. Gender-specific multiple regression models revealed that weaker instrumental self-efficacy beliefs predicted declines in reported functional status as measured by the Nagi performance scale among both men and women, independent of standard sociodemographic, health status, and health behaviors. Among men, instrumental efficacy beliefs were also negatively related to reports of onset of Katz ADL. Self-efficacy beliefs were unrelated to measured changes in actual physical performance abilities for both men and women. These findings suggest that self-efficacy beliefs have significant impacts on perceptions of functional disability, independent of actual underlying physical abilities. Through such influences on perceptions of disability, self-efficacy beliefs may importantly affect lifestyles and quality of life at older ages.

Activities of Daily Living↗

PubMed2006

Kinematic response characteristics of the CAREN moving platform system for use in posture and balance research.

The CAREN system is a new and unique device for use in postural and balance research in clinical settings due to its ability to independently perturb the support surface in each of six degrees of freedom. Users of this system need knowledge of its technical performance which is not available. The aim of this study was to determine the technical performance of the CAREN system by defining its kinematic response characteristics to two commonly used input functions (sine and ramp) for each of its six translational and rotational axes. The translational and rotational displacement, velocity and acceleration limits of the CAREN system suggest that it is a mid-range system with regard to single degree of freedom moving platform devices reported in the literature. The maximum average displacement cross-talk was 1.5% of the viable working range in any specified direction. The maximum average velocity cross-talk was 3.3% of its maximum velocity in any specified direction. The CAREN system was able to respond to ramp input functions within its displacement and velocity limits although, for short duration ramps, there was evidence that target velocity was not reached. It is concluded that the CAREN system is an appropriate device for postural and balance research with some unique features. This specification of its technical performance should help researchers to identify the tasks for which it is most suitable.

Biomechanical Phenomena↗

PubMed2004

Effect of acute static stretching on force, balance, reaction time, and movement time.

PURPOSE: The purpose of the study was to investigate the effect of an acute bout of lower limb static stretching on balance, proprioception, reaction, and movement time. METHODS: Sixteen subjects were tested before and after both a static stretching of the quadriceps, hamstrings, and plantar flexors or a similar duration control condition. The stretching protocol involved a 5-min cycle warm-up followed by three stretches to the point of discomfort of 45 s each with 15-s rest periods for each muscle group. Measurements included maximal voluntary isometric contraction (MVC) force of the leg extensors, static balance using a computerized wobble board, reaction and movement time of the dominant lower limb, and the ability to match 30% and 50% MVC forces with and without visual feedback. RESULTS: There were no significant differences in the decrease in MVC between the stretch and control conditions or in the ability to match submaximal forces. However, there was a significant (P < 0.009) decrease in balance scores with the stretch (decreasing 9.2%) compared with the control (increasing 17.3%) condition. Similarly, decreases in reaction (5.8%) and movement (5.7%) time with the control condition differed significantly (P < 0.01) from the stretch-induced increases of 4.0% and 1.9%, respectively. CONCLUSION: In conclusion, it appears that an acute bout of stretching impaired the warm-up effect achieved under control conditions with balance and reaction/movement time.

Adult↗

PubMed2007

The reliability and validity of the Four Square Step Test for people with balance deficits secondary to a vestibular disorder.

OBJECTIVE: To determine the reliability and validity of the Four Square Step Test (FSST) for use in people with balance deficits secondary to vestibular disorders, who frequently report falling and have difficulty with changes of direction. DESIGN: Cross-sectional descriptive study. SETTING: Outpatient clinic. PARTICIPANTS: Thirty-two people with balance deficits secondary to vestibular disorders (mean age, 63.7+/-17.8y) who were currently enrolled in a vestibular physical therapy program agreed to participate. INTERVENTIONS: Participants performed the FSST, the Timed Up & Go (TUG) test, an 11-m walk test during which walking speed was recorded, and the Dynamic Gait Index (DGI) and completed the Dizziness Handicap Inventory (DHI) and the Activities-Specific Balance Confidence (ABC) Scale. MAIN OUTCOME MEASURES: The main outcome measures were the FSST time, TUG results, DGI score, gait velocity, and DHI and ABC scores. Number of fall risk factors, as determined by published scores for people at risk for falling on the TUG test and gait speed, and number of falls were compared with FSST scores. RESULTS: The FSST has good reliability (intraclass correlation coefficient, model 3,1: .93; 95% confidence interval, .86-.96) and had good correlations with the other gait measures (correlation coefficients for the TUG, .69; gait speed, .65; DGI, -.51) and poor correlations with the DHI and the ABC (DHI, -.13; ABC, -.12). Multivariate linear regression showed that 51.5% of FSST performance was explained by TUG score and gait speed. The mean FSST time differed significantly between groups with 0 (n=12), 1 (n=12), or 2 to 3 (n=8) risk factors for falls (analysis of variance, F=10.02; P<.01). A cutoff score of greater than 12 seconds on the FSST was associated with a sensitivity of 80% and specificity of 92% for the identification of subjects with 1 or more risk factors for falls. CONCLUSIONS: The FSST is a reliable and valid tool for measuring the ability to perform multidirectional movements in people with balance deficits secondary to vestibular disorders.

Accidental Falls↗

PubMed2005

Control of MHC class II antigen presentation in dendritic cells: a balance between creative and destructive forces.

The antigen capturing and presenting abilities of dendritic cells (DCs) are developmentally regulated in a process known as maturation. During maturation, DCs increase several fold their surface expression of major histocompatibility complex class II (MHC II) molecules. This increase is accompanied with a dramatic change in localization of MHC II molecules, which are abundant in endosomal structures in immature DCs but located mostly on the plasma membrane in mature DCs. How these changes relate to antigen processing, generation of MHC II-peptide complexes, and trafficking of MHC II molecules, in the immature and mature states of DC development, has been a matter of debate. Here, we discuss the work carried out to characterize the biochemical and cell biological mechanisms that control MHC II antigen presentation in mouse and human DCs, and how these mechanisms relate to the function of the DC network in vivo. We conclude that the control checkpoints operate downstream of MHC II-peptide complex formation and expression on the plasma membrane, acting in accord with control of MHC II synthesis. Therefore, immature and mature DCs present antigens to T cells under steady state and inflammatory conditions. We advocate that the mechanisms regulating MHC II-peptide complex turnover should be emphasized as an important theme for future DC research.

Animals↗