THE MODIFIED STAR EXCURSION BALANCE AND Y-BALANCE TEST RESULTS DIFFER WHEN ASSESSING PHYSICALLY ACTIVE HEALTHY ADOLESCENT FEMALES.

BACKGROUND: The modified Star Excursion Balance Test (mSEBT) and Y-Balance Test (YBT) are two common methods for clinical assessment of dynamic balance. Clinicians often use only one of these test methods and one outcome factor when screening for lower extremity injury risk. Dynamic balance scores are known to vary by age, sex and sport. The physically active adolescent female is at high risk for sustaining lower extremity injuries, specifically to the anterior cruciate ligament (ACL). Thus clarity regarding the use of dynamic balance testing results in adolescent females is important. To date, no studies have directly compared the various outcome factors between these two dynamic balance tests for this population. PURPOSE: To determine if there was an association between the mSEBT and YBT scores for measured reach distances, calculated composite score and side-to-side limb asymmetry in the ANT direction in physically active healthy adolescent females. STUDY DESIGN: Cross-sectional study. METHODS: Twenty-five healthy, physically active female adolescents (mean age, 14.0 ± 1.3 years) participated. Reach distances, a composite score and side-to-side limb asymmetry for the mSEBT and YBT, for each limb, were compared and examined for correlation. RESULTS: There were significant differences and moderate to excellent relationships between the measured reach directions between the mSEBT and the YBT. Injury risk classification, based on limb asymmetry in the anterior reach direction, differed between the tests. However, the calculated composite scores from the two tests did not differ. CONCLUSIONS: Performance scores on a particular reach direction should not be used interchangeably between the mSEBT and YBT in physically active adolescent females, and should not be compared to previously reported values for other populations. LEVEL OF EVIDENCE: Level 3.

Motion of the anterior cruciate ligament during internal and external rotation at the knee: A cadaveric study.

Despite advances in our understanding of anterior cruciate ligament (ACL) anatomy and function, the change in position of the ACL during tibial rotation is not well understood. The purpose of this study was to quantify and compare the movements of the anteromedial (AM) and posterolateral (PL) bundles of the ACL during 15° of medial and lateral rotation (with & without a shear force). Cadaveric knees (12 male/12 female) were dissected and mounted at 90° of knee flexion. Anthropometric features of the ACL and distal femur were recorded, and each bundle was marked at: femoral attachment (FA), midpoint of ligament (MP), and tibial attachment (TA). Digital images of ACL motion in the frontal plane were taken as the tibia was rotated about a fixed femur. Using digitizing software, the change in position of the markers was quantified. Measurements suggested the ACL pattern of motion was consistent between sexes, regardless of shear force. The greatest amount of movement of both the AM and PM bundles occurred at the TA marker. The FA marker moved more during medial rotation, and the MP and TA markers moved more with lateral rotation. The 20 lb-shear force affected medial rotation most. This study is the first to quantify movement of the ACL during medial and lateral tibial rotation. Data should assist surgeons to select a graft position that is capable of replicating the rotational movement of the native ACL, and help improve three-dimensional stability of the ACL reconstructed knee. Clin. Anat. 30:861-867, 2017. © 2017 Wiley Periodicals, Inc.

A cadaveric study of the structural anatomy of the sternoclavicular joint.

Pathologies of the sternoclavicular (SC) joint are infrequent and effective management is often hindered by a limited understanding of the anatomy. In this study, we did macroscopic evaluations of the ligaments, the intra-articular disc, and the articulating surfaces of 25 SC joints. After removal of the joint capsule, the articulating surfaces of the sternal end of clavicle and the sternum were evaluated and the intra-articular disc was macroscopically examined. The anterior SC ligament covered the intra-articular disc, which divided the joint into a clavicular and a sternal part. A thin capsule, relatively lateral and medial from the anterior SC ligament, covered the two intra-articular parts. This means that the anterior SC ligament can be used as a landmark to enter into clavicular or sternal part of the SC joint. Posteriorly, there was a thick capsule without soft-spot or clear posterior SC ligament. Only the antero-inferior surface of the sternal end of every clavicle was covered by cartilage. Of the intra-articular discs 56% were incomplete. All of these incomplete discs displayed a central hole with signs of degeneration and fraying. This was associated with increased cartilage degeneration at the clavicular side. By experimental design (past and present), it would seem reasonable to assume that the incomplete types are caused by degeneration and are not developmental.

Accuracy and reliability of anterior cruciate ligament clinical examination in a multidisciplinary sports medicine setting.

OBJECTIVE: To investigate the accuracy and reliability of anterior cruciate ligament (ACL) clinical examination in a multidisciplinary sports medicine setting. DESIGN: Retrospective review of patient charting. SETTING: Community-based multidisciplinary sports medicine clinic. PATIENTS: One hundred twelve patients with surgically confirmed ACL tear. INTERVENTIONS: Review of therapist, physician, and orthopedic surgeon charting. MAIN OUTCOME MEASURES: Scoring for the anterior drawer, Lachman, and pivot shift tests completed during clinical examination. Coefficient of agreement (P(o)) was calculated for each assessment technique to determine the interrater reliability. Sensitivity of assessment was determined by comparing patient's arthroscopic surgical results against clinician's scoring. RESULTS: On average, P(o) values indicated only moderate levels of interrater reliability (anterior drawer, x = 0.57; Lachman, x = 0.45; pivot shift, x = 0.53), with great variation observed between clinician's scoring for each assessment technique. Accuracy testing demonstrated that the Lachman test had the highest level of sensitivity when administered by orthopedic surgeons (x = 86%) and that sensitivity varied greatly among clinician groups and by assessment technique (range, 15%-87%). CONCLUSIONS: In sports medicine, unreliable or inaccurate clinical examination confounds the clinician's ability to make informed decisions regarding appropriate patient referral and treatment interventions. Our results indicate that levels of accuracy and reliability for clinical examination of the ACL within a multidisciplinary sports medicine setting may be much lower than previously reported within the literature. Further research is needed to clarify whether a standardized approach to ACL clinical examination could enhance levels of accuracy and reliability among clinicians working in a multidisciplinary setting.

Reliability of the Ely's test for assessing rectus femoris muscle flexibility and joint range of motion.

Rehabilitative protocols and orthopadic research are significantly influenced by the ability to perform reliable measures of specific physical attributes or functions. The hypothesis was that the Ely's test for evaluating rectus femoris flexibility and joint range of motion (ROM) is a reliable clinical tool. Participants (n = 54) were between the ages of 18 and 45, and had no history of trauma. Three clinicians with orthopedic expertise assessed quadriceps flexibility and joint ROM using pass/fail and goniometer scoring systems. A retest session was completed 7 to 10 days later. Statistically, Kappa values for pass/fail scoring (intrarater $\bar {X}=0.52$, interrater $\bar {X}=0.46$) and ICC values (intrarater $\bar {X}=0.69$, interrater $\bar {X}=0.66$) for goniometer data both indicated that the Ely's test demonstrated only moderate levels of intra- and interrater reliability. Measurement error values (SEM = 4 degrees , ME = 4 degrees , and CV = 3%) and Bland and Altman plots (with 95% Limits of Agreement) further demonstrated the degree of intrarater variance for each examiner when executing the Ely's test in a clinical setting. Results call into question the statistical reliability of the Ely's test, and provide clinicians with important information regarding the reliability limits of the Ely's test when used to clinically evaluate flexibility and joint ROM in a physically active population. More research is required to determine the variables that may confound statistical reliability of this orthopedic technique that is commonly used in a clinical setting to assess function about the thigh region.

Structural parameters of the vastus medialis muscle and its relationship to patellofemoral joint deterioration.

Vastus medialis (VM) muscle dysfunction and abnormal limb alignment are commonly observed in patients who experience changes in patellofemoral joint (PFJ) function, leading many clinicians to assume that there is a direct relationship between VM structural parameters, leg alignment, and PFJ dysfunction. This study tested the hypothesis that there is a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of patellofemoral joint deterioration (PFJD). The dissection study used 32 limbs from 24 intact cadavers. Data were collected on limb alignment, angle of VM muscle fibers below the superior aspect of the patella, length of VM inserting on the medial aspect of the patella, and severity and location of PFJD. Parametric and nonparametric statistical analyses illustrated that PFJD was most commonly located on the middle third of the medial half of the patellar articular surface. The severity of PFJD did not vary with location. There was no significant correlation between any of VM insertion length, VM fiber angle, limb alignment, and PFJD location and severity lpar;r(2) < 0.34). The results of this study did not support the hypothesis of a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of PFJD in this subject group. Future research should examine the relationship between functional parameters of the entire quadriceps muscle group and PFJ dysfunction.

Structural parameters of the vastus medialis muscle.

This research was designed to evaluate musculoskeletal anatomy of the quadriceps region relative to the patellofemoral joint. The hypothesis for the study was that the oblique portion (VMO) of the vastus medialis muscle (VM) is anatomically positioned to function primarily as an active medial stabilizer of the patella. Because many clinicians believe that the VMO functions independently as an active medial stabilizer of the patellofemoral joint (PFJ), PFJ rehabilitation protocols commonly target the VMO in an attempt to restore normal joint mechanics. It is unclear whether this purported selective function is supported by the underlying anatomical structure. Through dissection of 32 limbs from 24 intact cadavers with normal patellar alignment, data were collected on VM fiber alignment and innervation, the presence of fascial plane, and the length of VM about the patella. Statistical analyses demonstrated that the oblique and long heads of the VM muscle had significantly different (P < 0.05) angles of fiber orientation, as expected. When measurements were taken relative to a vertical axis (standardizing limb alignment between cadavers), the difference in fiber angles between oblique and long heads of the VM was reduced significantly. Additionally, < 10% of the length of the VM muscle inserted directly on the medial aspect of the patella, and there was no anatomical evidence of a fascial plane or separate innervation for the oblique and long heads of the VM. The results of the study did not support the hypothesis that the VMO is anatomically positioned to function primarily as an active medial stabilizer of the patella.

Microbial ranking of porous packaging materials (exposure chamber method), ASTM method: collaborative study.

A collaborative study involving 11 laboratories was conducted to measure the microbial barrier effectiveness of porous medical packaging. Two randomly cut samples from each of 6 commercially available porous materials and one positive and one negative control were tested by one operator in each of 11 laboratories. Microbial barrier effectiveness was measured in terms of logarithm reduction value (LRV), which reflects the log10 microbial penetration of the material being tested. The logarithm of the final concentration is subtracted from that of the initial concentration to obtain the LRV. Thus the higher the LRV, the better the barrier. Repeatability standard deviations ranged from 6.42 to 16.40; reproducibility standard deviations ranged from 15.50 to 22.70. Materials B(53), C(50), D(CT), and E(45MF) differ significantly from the positive control. The microbial ranking of porous packaging materials (exposure chamber method), ASTM method, has been adopted First Action by AOAC INTERNATIONAL.

Effect of oxytetracycline-medicated feed on antibiotic resistance of gram-negative bacteria in catfish ponds.

The effect of oxytetracycline-medicated feeds on antibiotic resistance in gram-negative bacteria from fish intestines and water in catfish ponds was investigated. In experiments in the fall and spring, using ponds with no previous history of antibiotic usage, percentages of tetracycline-resistant bacteria in catfish intestines obtained from medicated ponds increased significantly after 10 days of treatment. In the fall, resistance of the intestinal and aquatic bacteria returned to pretreatment levels within 21 days after treatment. In the spring, resistance declined after treatment but remained higher than pretreatment levels for at least 21 days in intestinal bacteria and for 5 months in aquatic bacteria. Plesiomonas shigelloides, Aeromonas hydrophila, and Citrobacter freundii were isolated frequently in both spring and fall; Escherichia coli, Klebsiella pneumoniae, Edwardsiella tarda, and Enterobacter spp. were isolated primarily in the spring. Oxytetracycline treatment did not affect the distribution of bacterial species in the fall but may have accelerated a shift toward greater prevalence of members of the family Enterobacteriaceae in the spring. Multiple antibiotic resistance did not appear to be elicited by oxytetracycline treatment.

The appendage domain of the AP-2 subunit is not required for assembly or invagination of clathrin-coated pits.

Coated pits contain a resident membrane molecule(s) that binds clathrin AP-2 with high affinity. AP-2 binding to this site is likely to be the first step in coated pit assembly because this subunit functions as a template for the polymerization of clathrin into flat polygonal lattices. Integral membrane proteins involved in receptor mediated endocytosis cluster in the newly assembled pits as they invaginate and bud from the membrane. The AP-2 subunit is a multi-domain, molecular complex that can be separated by proteolysis into a brick-shaped core and ear-like appendage domains. We have used this property to identify the domain involved in the various stages of coated pit assembly and budding. We found that the core of AP-2 is the domain that binds both to membranes and to triskelions during assembly. Triskelions are perfectly capable of forming lattices on the membrane bound cores. Clathrin lattices bound only to core domains were also able to invaginate normally. Limited proteolysis was also useful for further characterizing the AP-2 binding site. Elastase treatment of the inside membrane surface released a peptide fraction that is able to bind AP-2 in solution and prevent it from interacting with membranes. Affinity purification of binding activity yielded a collection of peptides that was dominated by a 45-kD species. This is the candidate peptide for containing the AP-2-binding site. Therefore, the appendage domain does not directly participate in any of the assembly or invagination events required for coated pit function.

Virulence characteristics of clinical and environmental isolates of Vibrio vulnificus.

Twenty-four randomly selected clinical and environmental Vibrio vulnificus isolates were tested for virulence in iron-overloaded mice (250 mg of iron dextran per kg of body weight). The log10 50% lethal doses of 17 isolates were lower by greater than or equal to 3.5 log10 units in iron-overloaded mice than in control mice. These isolates were classified as virulent. The 50% lethal doses of these virulent isolates were also lower in mice that were immunosuppressed by treatment with cyclophosphamide (150 mg/kg). Four of the seven isolates initially classified as avirulent were virulent in mice that were simultaneously iron overloaded and immunosuppressed. These isolates were classified as moderately virulent. The remaining three isolates were avirulent under all conditions. The incidence of virulent strains among clinical and environmental isolates did not differ. The virulent isolates produced high titers of hemolysin, were resistant to inactivation by serum complement, produced phenolate siderophore, and utilized transferrin-bound iron. The moderately virulent isolates differed from the virulent isolates only in their increased sensitivity to inactivation by serum complement. The avirulent isolates differed from those of the other two classes in their inability to either produce significant amounts of phenolate siderophore or utilize transferrin-bound iron. A modified agar plate diffusion method for transferrin-bound iron utilization was developed to differentiate the two classes of virulent isolates from the avirulent isolates in vitro.

Thermotolerance of heat-shocked Listeria monocytogenes in milk exposed to high-temperature, short-time pasteurization.

The effect of prior heat shock (48 degrees C for 15 min) on the thermotolerance of Listeria monocytogenes at the minimal high-temperature, short-time (71.7 degrees C for 15 s) parameters required by the Pasteurized Milk Ordinance was examined. The mean D71.7 degrees C value for heat-shocked L. monocytogenes was 4.6 +/- 0.5 s (control D = 3.0 +/- 1.0 s); the ratio of D to control D was 1.5. The increased thermotolerance of heat-shocked Listeria cells was not significant and appeared unlikely to have practical implications, in terms of risk assessment, for the safety of pasteurized milk.

Thermotolerance of Listeria monocytogenes and Salmonella typhimurium after sublethal heat shock.

The effect of prior heat shock on thermotolerance of Listeria monocytogenes and Salmonella typhimurium in broth culture was determined. Bacteria were grown at the permissive temperature of 35 degrees C, sublethally heated at 35 (control), 42, 48, and 52 degrees C (nonpermissive control) for various times, and inactivated at either 57.8 or 52 degrees C. The induction of increased thermotolerance by heat shock, although consistent within each experiment, was generally not significant for L. monocytogenes; the increase was significant for S. typhimurium. Temperature shift experiments with L. monocytogenes suggested that induced thermotolerance was not long lived unless the shock temperature was maintained.

Clathrin-coated pits contain an integral membrane protein that binds the AP-2 subunit with high affinity.

Coated pits will assemble onto purified plasma membranes that are attached to a poly-L-lysine coated substratum (Moore, M. S., Mahaffey, D. T., Brodsky, F. M., and Anderson, R. G. W. (1987) Science 236, 558-563; Mahaffey, D. T., Moore, M. S., Brodsky, F. M., and Anderson, R. G. W. (1989) J. Cell Biol. 108, 1615-1624). To better understand the assembly reaction, we have purified both clathrin triskelion and AP-2 subunits from bovine brain and assayed for their ability to bind to the cytoplasmic surface of attached membranes. Two types of membranes were analyzed: those washed with a high pH buffer that selectively removes triskelions and those washed with a high salt buffer that removes both the AP-2 and the triskelion subunits. We found that purified AP-2 subunits bind with high affinity (Kd approximately 3 x 10(-8) M) to salt stripped membranes. Binding is saturable and abolished by treating membranes with less than 20 micrograms/ml of elastase. When membranes were treated with elastase before the salt wash and then salt washed and assayed for AP-2 binding, normal binding was seen, which indicates that the presence of clathrin-coated pits protects the binding site from the protease. Membranes that had rebound AP-2 did not bind purified triskelions, even though high pH buffer-washed membranes that bear endogenous AP-2 bound triskelions with high affinity (Kd approximately 3 x 10(-9) M) and supported lattice assembly. We conclude that coated pit assembly is initiated by the binding of AP-2 to an integral membrane protein but that the AP-2 complex must be activated by an unknown process before the coated pit lattice will assemble.

Incidence of Vibrio parahaemolyticus in U.S. coastal waters and oysters.

Oyster and seawater samples were collected seasonally from May 1984 through April 1985 from shellfish-growing areas in Washington, California, Texas, Louisiana, Alabama, Florida, South Carolina, Virginia, and Rhode Island which had been designated as approved or prohibited by the National Shellfish Sanitation Program. Fecal coliforms counts, aerobic plate counts, and Vibrio parahaemolyticus densities were determined for the samples. Mean V. parahaemolyticus density was more than 100 times greater in oysters than in water, whereas density of fecal coliforms was approximately 10 times higher in oysters. Seasonal and geographical distributions of V. parahaemolyticus were related to water temperature, with highest densities in samples collected in the spring and the summer along the Gulf coast. The synthetic DNA probe for thermostable direct hemolysin hybridized with 2 of 50 isolates, 1 of which was positive by the Kanagawa test.

Precision parameters of standard methods of analysis for dairy products.

The available collaborative studies for standard methods of analysis for various constituents of milk and milk products were examined in an attempt to assign specific repeatability and reproducibility precision parameters to these methods. The different collaborative assays for the primary constituents (moisture/solids, fat, protein), the nutritionally important elements (calcium, sodium, potassium, phosphorus), and miscellaneous analytes/physical constants (ash, lactose, salt, freezing point) produced different estimates of the precision parameters for the same method. A suitable summary of the precision estimates from collaborative studies is given by the reproducibility relative standard deviation, RSDg, which is relatively constant within a product and permits comparisons across products. An estimate of the variation of RSDR for an analyte from a number of collaborative studies is presented in terms of the median and 90% interval (the range of the centermost 90% of values). These estimates are only informative when a substantial number of independent studies are available for pooling the independent estimates to form a distribution of RSDR values. The RSDR for the determination of the primary constituents of milk and milk products is characterized by a median RSDR of 1% and a 90% interval of 0.3-3%, with RSDR estimates occasionally occurring below 0.3% and above 4%. These overall estimates appear to be independent of analyte, matrix, and method and apply to concentrations of primary constituents that range from about 2 to 80%. The repeatability relative standard deviation, RSDr, is unstable, although it tends to converge to about 0.5-0.7 X RSDR. Too few collaborative assays are available to characterize RSDR for the determination of certain other constituents (acidity, ash, lactose, salt, and the nutritionally important elements) unless RSDR values for different analytes, methods, and matrixes are pooled on the basis of similar analyte concentrations. When pooled, the RSDR values are generally better than predicted from the Horwitz equation, RSDR (%) = 2 exp (1-0.5 log10C), where C is the concentration expressed as a decimal fraction; all but one of 661 RSDR values are within the upper empirical limit of twice this curve.

Listeria spp. found on fresh market produce.

From October 1987 to August 1988, 1,000 tests were conducted on 10 types of fresh produce from two Minneapolis area supermarkets to detect Listeria spp. The produce included broccoli, cabbage, carrots, cauliflower, cucumbers, lettuce, mushrooms, potatoes, radishes, and tomatoes. The vegetables were tested by the Food and Drug Administration method for isolation of Listeria spp., with the addition of LiCl-phenylethanol-moxalactam agar in the last 280 tests; 8.6 and 11.4% of these tests were positive by modified McBride and LiCl-phenylethanol-moxalactam agars, respectively. Listeria monocytogenes was isolated from cabbage, cucumbers, potatoes, and radishes; L. innocua was isolated from cucumbers, lettuce, mushrooms, potatoes, and radishes; L. seeligeri was isolated from cabbage and radishes; and L. welshimeri was isolated from cucumbers, potatoes, and radishes. The isolates were of various serotypes; however, the L. monocytogenes isolates were predominantly serotype 1 (82%). Only potatoes (25.8% positive) and radishes (30.3% positive) showed significant amounts of L. monocytogenes contamination.

Comparative recovery of uninjured and heat-injured Listeria monocytogenes cells from bovine milk.

The standard selective enrichment protocols of the Food and Drug Administration (FDA) and U.S. Department of Agriculture (USDA) were compared with an experimental nonselective broth enrichment (NSB) protocol and variations of the standard cold-enrichment (CE) protocol for the recovery of heat-injured Listeria monocytogenes. Bacterial cells (10(7)/ml) were suspended in sterile milk and heated at 71.7 degrees C in a slug-flow heat exchanger for holding times ranging from 1 to 30 s. Surviving cells were determined (50% endpoint) by the given protocols, and the following D values were obtained: NSB, D = 2.0 +/- 0.5 s; FDA, D = 1.4 +/- 0.3 s; USDA, D = 0.6 +/- 0.2 s; CE, D less than or equal to 1.2 s. The respective direct-plating media used in these enrichments were also analyzed for recovery, and the following D values were calculated from the enumeration of surviving cells; NSB, D = 2.7 +/- 0.8 s; FDA, D = 1.3 +/- 0.4 s; USDA, D = 0.7 +/- 0.2 s. The low levels of heat-injured L. monocytogenes cells which were detected at inactivation endpoints on the optimal nonselective media (25 degrees C for 7 days) failed to recover and multiply during experimental CEs (4 degrees C for 28 days). Initial inactivation experiments in which raw whole milk was used as the heating menstruum gave much lower recoveries with all protocols. The detectable limits for uninjured cells that were suspended in raw milk were similar (0.35 to 3.2 cells per ml) for the standard CE, FDA, and USDA protocols.(ABSTRACT TRUNCATED AT 250 WORDS)

Phagocytosis of particulate antigens by corneal epithelial cells stimulates interleukin-1 secretion and migration of Langerhans cells into the central cornea.

Under normal physiological conditions, the central corneal epithelium is devoid of Ia+ Langerhans cells. However, a variety of stimuli can induce the migration of peripheral Langerhans cells into the central regions of the cornea. In the present study, Langerhans cell migration was induced by the instillation of either sterile latex beads or formalin-killed Staphylococcus aureus into shallow incisions in the central corneal epithelium. Langerhans cells could be detected in the central cornea as early as 24 hours following instillation of either latex beads or S. aureus and remained for at least 6 weeks. Phagocytosis of latex beads by corneal epithelial cells was demonstrated in vivo and in vitro. Moreover, phagocytosis of latex beads stimulated corneal epithelial cells to secrete increased amounts of interleukin-1 (21-83% increase). The centripetal migration of peripheral corneal Langerhans cells in response to phagocytosis of latex beads could be mimicked by injecting as little as 0.001 units of human purified interleukin-1 (IL-1) into the central corneal epithelium. The IL-1 induced chemotaxis could be blocked by coinjection of anti-IL-1 antibody but not irrelevant antibody. The findings indicate that the exclusion of Langerhans cells from the central corneal epithelium is a dynamic process that can be regulated by the resident corneal epithelial cells themselves and raises the possibility that corneal epithelial cells and Langerhans cells collaborate in antigen processing within this organ.

The immunogenic privilege of corneal allografts.

Corneal grafts enjoy the highest success rate of any form of organ transplantation. The low incidence of graft rejection is particularly impressive considering that human leukocyte antigen matching of donor and recipient is not normally performed. Although corticosteroids are applied topically, systemic immunosuppressive drugs are not routinely implemented for keratoplasty. The most widely accepted explanation to account for corneal allograft success suggests that the avascularity of the graft bed prevents corneal alloantigens from reaching the regional lymphoid tissues and therefore results in an "afferent blockade" of the immune response. However, recent findings suggest that the unique immunologic characteristics of the corneal graft itself may play a crucial role in determining the fate of the transplant. In particular, the presence and distribution of donor-derived Ia+ Langerhans cells can have a profound impact on graft immunogenicity and thus, graft survival even if the graft bed is initially free of lymphatic and blood vascular drainage channels. Thus, the immunologically unique characteristics of the corneal graft conspire with the avascular graft bed to produce an "immunologically privileged" environment that promotes graft survival.