FTIR Spectroscopy Detects Intermolecular β-Sheet Formation Above the High Temperature Tm for Two Monoclonal Antibodies

The temperature-dependent secondary structure of two monoclonal IgG antibodies, anti-IGF1R and anti-TSLP, were examined by transmission mode Fourier Transform Infrared (FTIR) spectroscopy. Anti-IGF1R and anti-TSLP are IgG monoclonal antibodies (mAbs) directed against human Insulin-like Growth Factor 1 Receptor for anti-tumor activity and Thymic Stromal Lymphopoietin cytokine for anti-asthma activity, respectively. Differential scanning calorimetry (DSC) clearly indicates both antibodies in their base formulations have a lower temperature protein conformational change near 70 °C (T_m1) and a higher temperature protein conformational change near 85 °C (T_m2). Thermal scanning dynamic light scatting (TS-DLS) indicates a significant particle size increase for both antibodies near T_m2 suggesting a high level of protein aggregation. The nature of these protein conformational changes associated with increasing the formulation temperature and decreasing sucrose concentration were identified by transmission mode FTIR and second derivative FTIR spectroscopy of temperature controlled aqueous solutions of both monoclonal antibodies. The transition from intra-molecular β sheets to inter-molecular β sheets was clearly captured for both monoclonal antibodies using FTIR spectroscopy. Finally, FTIR Spectroscopy was able to show the impact of a common excipient such as sucrose on the stability of each monoclonal antibody, further demonstrating the usefulness of FTIR spectroscopy for studying protein aggregation and formulation effects.

Ultrasound is now better than mammography for the detection of invasive breast cancer

OBJECTIVE

This study investigated the use of ultrasound (US) as a first-line diagnostic tool.

METHODS

All women attending our breast center underwent bilateral whole-breast US in addition to all other investigations, and results were documented prospectively and preoperatively.

RESULTS

Of 796 patients with breast cancer, US was positive in 710 (89%) and mammography in 706 (89%) (P = not significant). Either US or mammogram was positive in 770 (97%). Of 537 (67%) symptomatic patients, US was positive in 497 (93%) and mammography in 465 (87%). Either US or mammography was positive in 515 (96%). Of 259 (33%) screening patients, 220 (85%) had invasive cancer. US was positive in 195 (89%) and mammography in 203 (92%) (P = not significant). Either US or mammography was positive in 217 (99%). Of 39 screening patients with ductal carcinoma in situ (5% of all patients), US was positive in 18 (46%) and mammography in 38 (97%).

CONCLUSIONS

US is significantly better than mammography for detecting invasive breast cancer (92% patients). The combination of US and mammography is significantly better than either modality used alone, together resulting in 9% more breast cancers detected.

Longitudinal evaluation of bovine mammary gland health status by somatic cell counting, flow cytometry, and cytology

Bovine mastitis phases induced by Staphylococcus aureus were assessed in 6 lactating cows before challenge and at 1, 4-8, and 9-14 days postinoculation (dpi). Milk lymphocytes, macrophages, and polymorphonuclear cells (PMN) were counted by conventional (manual) cytology, identified by CD3+ and CD11b+ immunofluorescence and counted by flow cytometry (based on leukocyte forward and side light scatter values). Somatic cell counts (SCC) and recovery of bacteria were recorded at the same times. Preinoculation samples showed a lymphocyte-dominated composition. At 1 dpi, the percentage of PMN increased and that of lymphocytes decreased. At 4-8 dpi, PMN were predominant, but the percentage of mononuclear cells increased above that at 1 dpi and further increased by 9-14 dpi (when lymphocytes approached prechallenge values). Based on leukocyte percentages, 3 indices were created from the data: 1) the PMN/lymphocyte percentage ratio (PMN/L), 2) the PMN/macrophage percentage ratio (PMN/M), and 3) the phagocyte (PMN and macrophage)/lymphocyte percentage ratio (Phago/L). Significant correlations were found between cytologic and flow cytometric data in all of these indicators (all with P < or = 0.01). These indices identified nonmastitic, early inflammatory (1-8 dpi), and late inflammatory (9-14 dpi) animals. In contrast, SCC and bacteriology did not. Although sensitivity of the SCC was similar to that of Phago/L, the specificity of SCC was almost half that of the Phago/L index. Based on flow cytometry indicators, an algorithm for presumptive diagnosis of bovine mastitis was developed. Flow cytometry provides results as valid as those obtained by conventional (manual) cytology, shows greater ability to identify mastitic cases than does SCC, and may identify 3 mammary gland health-related conditions.

Breast cancer audit: adapting national audit frameworks for local review of clinical practice

OBJECTIVE

To assess the value of using a nationally devised data set for breast cancer audit at a local level for reviewing clinical practice.

DESIGN

Audit proforma based on the Scottish Cancer Therapy Network (SCTN) minimum data set and database completed prospectively from January 1999.

SETTING

Hairmyres Hospital, a district general hospital within Lanarkshire Acute Services NHS Trust.

SUBJECTS

The inclusion criteria were those developed by SCTN for the core minimum data set for breast cancer (SCTN 1999).

RESULTS

The results indicate that the SCTN minimum data set can be usefully employed to collect prospective data on breast cancer. The data set is sensitive enough to identify any problem areas, which can be reviewed at greater detail when required. This datset is a robust mechanism for collecting meaningful and comparable data both at a local and national level.

CONCLUSIONS

The use of SCTN's minimum data set has been successful for local review of practice. This has led to the identification of "out-liers" from the normal range of process indicators and further internal examination of these at a local level by individual clinicians is under way. This exercise has also proved fruitful in identification of other fields, which can be added to the data set to refine the data collected. The database provided by SCTN is easily manipulated allowing for refinement where required. Breast cancer audit carried out in this way is a useful way of reflecting on clinical practice throughout the multidisciplinary team.

Dipodascus starmeri sp. nov., a new species of yeast occurring in cactus necroses

In a previous publication describing the geographic distribution of yeasts associated with cactus necroses (W. T. Starmer, M.-A. Lachance, H. J. Phaff, and W. B. Heed, Evol. Biol. 24:253-296, 1990), 127 isolates were identified as strains of Candida ingens van der Walt et van Kerken on the basis of morphology and certain phenotypic characteristics. Here we show by using DNA hybridization and additional phenotypic properties that these strains were misidentified and that they represent a minimum of three separate species that can be differentiated from C. ingens and from each other by utilization of 2-propanol or acetone, sensitivity to digitonin, utilization of L-lysine as a sole nitrogen source, vitamin dependence, NaCl tolerance, lipolytic activity, and habitat. One of the new species is haploid and heterothallic, and its teleomorph represents the genus Dipodascus. We describe Dipodascus starmeri sp. nov. The phylogenetic relationship of D. starmeri with other members of the genus Dipodascus and its anamorph, the genus Geotrichum, was estimated from ribosomal DNA nucleotide sequence divergence. The type strain, a heterothallic haploid isolate, is UCD-FST 72-316 (= CBS 780.96 = ATCC 200546 = NRRL Y-17816). The complementary mating type is UCD-FST 81-513.3 (= CBS 781.96 = ATCC 200547 = NRRL Y-17817).

The role of the breast physician in the multidisciplinary breast centre

The term breast physician was coined in Australia in 1990 to describe a female medical practitioner who is skilled in interpreting screening mammograms and the diagnostic work-up of women with symptomatic breast problems. The Australian Society of Breast Physicians was formed in 1990, and in 1995 became the Australasian Society to incorporate the New Zealand breast physicians. There is now a network of breast physicians throughout Australia who are involved in breast screening clinics or breast diagnostic centres. Thirty women doctors in the United Kingdom work in a similar role. The role of the breast physician is a new, exciting and challenging career option for women doctors. The authors believe that breast physicians have an important role in the diagnosis, treatment and follow up of women with symptomatic breast problems.

Pharmacologic profile of diaspirin cross-linked hemoglobin in hemodialysis patients

Various hemoglobin compounds have been evaluated as potential oxygen-carrying, blood volume expanders, but toxicity has prevented clinical application. Diaspirin cross-linked hemoglobin (DCLHb) represents a modified hemoglobin compound that is derived from human red blood cells and maintained in a tetrameric configuration by cross-linkages between the two alpha chains of the hemoglobin molecule. In a randomized, placebo-controlled, single-blind, cross-over trial, DCLHb's safety and pharmacologic parameters were evaluated in 18 subjects receiving chronic hemodialytic therapy. A 30-minute infusion of 25, 50, or 100 mg/kg DCLHb or placebo was given at the start of routine hemodialysis. One week later, the alternate treatment (placebo or DCLHb) was administered. Maximum plasma hemoglobin concentrations and terminal half-life values were calculated for each dosage group. Dialysate was collected and assayed for hemoglobin. Changes in systolic and diastolic blood pressure from baseline and the volume of hypertonic saline administered for treatment of hypotension during hemodialysis were measured. The maximum plasma hemoglobin concentrations increased with DCLHb dose and occurred at the end of DCLHb infusion. The mean (+/- SD) terminal half-life ranged from 2.1 +/- 1.0 hours in the 25 mg/kg DCLHb group to 4.3 +/- 1.4 hours in the 100 mg/kg group, but did not differ significantly between groups. Mean baseline plasma hemoglobin corrected areas under the plasma concentration-time curves increased from 89 to 1,136 mg/hr/dL across the fourfold dose range. Diaspirin cross-linked hemoglobin was not dialyzable as none was detected in dialysate. The maximum increase in systolic blood pressure from baseline increased significantly with DCLHb dose compared with placebo (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between exercising humans and growing plants in a Closed Ecological Life Support System

The purpose of this study was to quantify the gas exchange between plants growing in a Closed Environmental Life Support System (CELSS) and the metabolism of human subjects undergoing various levels of physical exercise, and subsequently determine the buffer characteristics in relation to the carbon exchange established for plants in this closed loop life support system. Two men (ages 42 and 45 yr) exercised on a cycle ergometer at three different work intensities, each on a separate day. The CELSS, a 113 m3 chamber, was sized to meet the needs of one human. The plants, consisting of 20 m2 of potato, provided oxygen to the human during an artificially lighted photosynthesis phase and the human provided CO2 to the plants. The average rates of exchange for the subjects were 0.88, 1.69, and 2.47 liters O2/min and 0.77, 1.47, and 2.21 liters CO2/min at approximately 25%, 50%, and 75% of their maximal aerobic capacity, respectively. The photosynthetic rate for the CELSS was 0.95 liters/min. A balance between human CO2 production and plant utilization was noted at approximately the 50% VO2max level. The oxygen balance and changes were not within detectable limits of the CELSS instrumentation for the durations of these exercise exposures. If a CELSS environment is the methodology selected for long term spaceflight, it will be important to select plants that efficiently grow at the available light and nutrient levels while balancing the needs for the human crew at their levels of physical activity.

Renal failure in a calf secondary to chronic enteritis

This clinical report describes a case of renal failure in a Holstein calf. It is suggested that the renal failure was hemodynamically-mediated. The combination of a chronic enteritis and failure to ingest adequate fluids produced the hyponatremia, hypochloremia, and metabolic acidosis. The elevated BUN, creatinine, FENa, and isosthenuria confirmed the diagnosis of renal failure. Continued testing of the heifer demonstrated persistence of the renal failure even though the heifer appeared normal on clinical examination. Monitoring the growth rate of the heifer calf demonstrated a severe reduction when compared to age-matched herdmates.

Granulated round cell tumor of cats

Morphologic and biologic features of five feline granulated round cell tumours were compared with those previously reported to be of globule leukocyte and large granular lymphocyte origin. The five cats ranged from 6 to 9 years of age and presented with nonspecific gastrointestinal signs. Four of the five cats were tested for feline leukemia virus and were negative by enzyme-linked immunosorbent assay. The neoplastic process involved the abdominal cavity in all cases, with a predilection for the distal small intestine and mesentery. The liver and peripheral and thoracic lymphoid tissues were also sporadically affected. Neoplastic round cells contained 0.5-1.5-microns eosinophilic cytoplasmic granules that were difficult to discern on causal observation with hematoxylin and eosin stain but were deep blue and easily visualized when stained with phosphotungstic acid-hematoxylin. In two cases, epithelium in the affected ileum and liver contained unusually large numbers of apparently normal globule leukocytes. Ultrastructurally, the tumor granules tended to cluster at one nuclear pole and were spindle to round in shape with variably dense contents. Some granules contained a dense "cap" at one end or internal crystalloid bars that distorted the granule membrane. The tumors reported herein are similar to all three of the previously reported feline granulated round cell tumors and probably have a common cellular origin.

Social cognitions as organizers of autonomic and affective responses to social challenge

Autonomic and affective responses to children were assessed as a function of adult perceptions of interpersonal control. Women (N = 160) interacted with and provided feedback to computer-simulated children who "behaved" responsively or unresponsively on a computer game. Women were categorized as low in perceived control (PC) if they attributed high control to children but low control to self over negative events on the Parent Attribution Test. As predicted, low-PC women were maximally reactive to child characteristics, manifesting peak levels of defensive arousal (increased level of heart rate and electrodermal activity) and negative affect with unresponsive children and minimal levels of arousal and negative affect with responsive children. Intermediate response levels were shown by high-PC Ss. We interpreted results as suggesting mediating factors that may operate in dysfunctional interaction patterns previously found for low-PC caregivers.

Social cognitions as organizers of autonomic and affective responses to social challenge

Autonomic and affective responses to children were assessed as a function of adult perceptions of interpersonal control. Women (N = 160) interacted with and provided feedback to computer-simulated children who "behaved" responsively or unresponsively on a computer game. Women were categorized as low in perceived control (PC) if they attributed high control to children but low control to self over negative events on the Parent Attribution Test. As predicted, low-PC women were maximally reactive to child characteristics, manifesting peak levels of defensive arousal (increased level of heart rate and electrodermal activity) and negative affect with unresponsive children and minimal levels of arousal and negative affect with responsive children. Intermediate response levels were shown by high-PC Ss. We interpreted results as suggesting mediating factors that may operate in dysfunctional interaction patterns previously found for low-PC caregivers.

Influences of witnessed affect on information processing in children

Children between the ages of 5 and 10 years watched a videotape of a child having a routine medical exam. Embedded within the scenes were systematic variations of depicted facial affect shown by doctor and child. Measures were taken of autonomic reactions and information-processing errors in response to positive, neutral, and negative affective cues. For 5-6-year-olds, processing errors were greatest in the negative affect condition. Additionally, peak increases in heart rate (HR) and skin conductance level (SCL) were demonstrated by 5-6-year-olds in response to negative affect shown by the witnessed child; increases in HR were in turn predictive of processing errors. Older children (9-10 years) showed trends reflecting reduced processing errors in response to witnessed negative affect. It was suggested that younger children respond to salient threat cues with a "defensive" response pattern that is relatively adaptive at younger but not older ages.

New directive for documentation review in radiation oncology

A new directive from the Health Care Financing Administration regarding reimbursement for daily patient care underscores the importance of accurate documentation in radiation oncology. Ms. Blue describes a quality control system in use at her institution which involves a comparison of what is documented in the medical record with what has been charged.

Pulmonary aspergillosis in a horse with myelomonocytic leukemia

Acute myelomonocytic leukemia was diagnosed in a 2-year-old Standardbred mare that had hind limb edema and fever unresponsive to antibiotics. The mare had anemia, thrombocytopenia, and leukocytosis, with circulating myeloblasts and monocytoid cells. A bone marrow specimen was hypercellular, with myeloblasts and monocytoid cells. Peroxidase, chloroacetate esterase, and alpha naphthyl acetate esterase activities were detected in many bone marrow cells. Interstitial pulmonary densities were seen radiographically. The mare was euthanatized and necropsied. Infiltrates of leukemic cells were found microscopically in specimens of spleen, lymph nodes, liver, kidneys, gastrointestinal tract, and lungs. Granulomas containing fungal hyphae were seen microscopically in the lungs, and Aspergillus sp was isolated from the lesions.

Biological considerations for treating alternate fields versus all fields daily with high and low LET radiation

The rationale for treating all fields every day with photons was reviewed. Since the effects of neutron radiation are much less dependent on alterations of fractionation schedules, and since preferential sparing for late effects is not obtained by fractionation of neutron dose, less convincing reasons exist for treating all fields every day with neutrons. Treating one field/day would not alter the physical dose distribution or overall treatment time, yet still maintain biological homogeneity. Preliminary in vitro experiments support this conclusion.

Urinary tract infection due to indwelling bladder catheters in dogs and cats

Urine samples were collected from 27 dogs and 4 cats with indwelling urinary catheters connected to a closed system. Twenty-one animals had sterile urine at the initiation of catheterization. Eleven of these 21 animals developed positive urine culture after 4 (mean) days (range 1 to 10 days) of catheterization. Infections persisted after catheter removal in 6 of 8 animals. The 10 animals that did not develop bacteriuria had a shorter duration of catheterization (3 days vs 12 days, mean). Antibiotics (chloramphenicol, trimethoprim/sulfonamide, cephradine, lincomycin, gentamicin, or ampicillin) were used during the period of catheterization in 17 of 21 animals, 8 of which developed bacteriuria and 9 of which did not. Ten animals had bacteriuria at the initiation of urine collection for culture. The type of bacteria changed during the catheterization period in 6 animals, all of which were given antibiotics. Bacteria isolated from animals given antibiotics seemed to become increasingly antibiotic-resistant.

Behavior problems and social competence in girls with true precocious puberty

We report a controlled standardized behavioral assessment of 33 girls with true precocious puberty using the Child Behavior Checklist. Although a majority of the girls were reported not to have behavior problems, many were reported to have a dysphoric adjustment to their condition. Twenty-seven percent of the girls with true precocious puberty scored greater than 2 SD above the mean on the Total Behavior Problem scale 10 times the expected prevalence rate. They also scored significantly higher (P less than 0.01) than matched controls on both the internalizing or "overcontrolled symptom" and externalizing or "undercontrolled symptom" scales. Forty-eight percent scored greater than 2 SD above the mean on the Social Withdrawal scale. The high prevalence of reported problem behaviors in this sample may be related directly or indirectly to the precocious maturation mediated by biologic, psychologic, social, and environmental variables. Although elevated levels of sex steroids may directly contribute to increased aggressive and hyperactive behaviors, they may also be modified by social and environmental factors.

Vascular pathways in nonsinusal red pulp--an electron microscope study of the cat spleen

The red pulp of the cat spleen, including terminal segments of arterial capillaries, pulp venules, and the reticular meshwork, was studied by transmission electron microscopy. Splenic congestion and contraction were produced by barbiturate anesthetic and norepinephrine. Terminal segments of arterial capillaries were ampullary and flared. Blood escaped into surrounding pulp spaces through interendothelial gaps. Pulp venules originated as open-ended vessels in the reticular meshwork near trabeculae and drained into trabecular veins. Venule walls were thin and composed of squamous endothelial cells, a continuous basement membrane, and reticular cells. Venules in congested spleens had many mural apertures, but venules in contracted spleens had few. The interstices of the reticular meshwork in congested spleens contained large amounts of blood, which often was concentrated, many macrophages, lymphocytes, and plasma cells. Fewer blood cells and scant plasma were present in contracted spleens. The vascular arrangements are anatomically open. Blood takes pathways through the reticular meshwork from arterial terminations to pulp venules. Some pathways through the reticular meshwork probably function as closed vascular channels conveying rapidly flowing blood. Other pathways are functionally open and probably contain slowly moving blood that constitutes a reservoir of red cells. Macrophages formed associations with mature red cells and with reticulocytes. Mature red cells were attached to macrophages in a manner indicating erythrophagocytosis. Reticulocyte attachment had a different appearance and likely resulted in reticulocyte sequestration. Platelets bore pseudopodia which would impede their passage through irregular and cell-filled pulp spaces. The change in platelet shape probably is responsible for the formation of the splenic pool of platelets.

Species variation in the structure and function of the marginal zone--an electron microscope study of cat spleen

The marginal zone in the cat spleen consisted of a characteristic mixture of lymphocytes and other blood cells located mainly between the several layers of circumferential reticulum around white pulp. A region of fine-meshed reticulum between white pulp and red pulp, as present in some species, was absent from the cat spleen. Arterial capillaries to the marginal zone were few. Some were continuations of white pulp capillaries, whereas others were red pulp capillaries that likely were continuations of axial capillaries of periarterial macrophage sheaths (PAMS) (ellipsoids). Blood cells deposited in the marginal zone could reach red pulp by passing through the numerous openings in each layer of circumferential reticulum. Lymphocytes appeared to migrate across the marginal zone both toward and away from white pulp. Macrophages lying on the circumferential reticulum of the marginal zone phagocytized cells but did not ingest Thorotrast, although it coated their surfaces. Because of the scarcity of arterial endings and the lack of a macrophage-charged reticular meshwork, the marginal zone in cat spleen is not a major site of blood clearance and phagocytosis. These functions are better served in PAMS and red pulp.

Electron microscopy of the red pulp of the dog spleen including vascular arrangements, periarterial macrophage sheaths (ellipsoids), and the contractile, innervated reticular meshwork

The vascular and stromal arrangements of the red pulp in congested and contracted dog spleens were studied by transmission electron microscopy. Each dog had been injected intravenously with Thorotrast to label actively endocytizing cells. Only macrophages ingested Thorotrast. The proximal portion of each arterial capillary was surrounded by a "periarterial macrophage sheath" (PAMS), a term we introduce to replace the term "ellipsoid". PAMS were composed of a fine meshwork of reticular cells and reticular fibers which held tightly-packed macrophages and interspersed blood cells. These macrophages, as well as those in the reticular meshwork of red pulp, contained Thorotrast, cell debris, and deposits of hemosiderin. The arterial capillary at the center of each PAMS was formed by parallel, rod-shaped endothelial cells and discontinuous layers of basement membrane and reticular-cell cytoplasm. PAMS were tapered at their distal ends; the terminal portion of the arterial capillary continued beyond the PAMS to end in the reticular meshwork of red pulp. Endothelial cells in the terminal arterial capillaries were separated by gaps through which blood cells passed into the spaces of the reticular meshwork of red pulp. The reticular meshwork was formed by reticular cells which appeared to be specialized for contraction. These cells were filled with thin filaments and possessed plasmalemmal dense bodies as found in smooth muscle cells. Furthermore, the reticular meshwork was innervated by unmyelinated adrenergic axons which probably were derived from nerves that followed arterioles. Axons were enclosed in surface invaginations of cells which were similar to reticular cells in shape and cytologic detail and which we called "axon-bearing reticular cells". Axon-bearing reticular cells were inserted between the branches of the reticular cells that formed the meshwork. Venous sinuses formed an anastomosing system of vessels draining into pulp veins which then joined trabecular veins. Sinuses were formed by parallel, rod-shaped endothelial cells encircled by strands of basement membrane and reticular-cell branches. Endothelial cells lay closely side by side except where interendothelial slits were opened by blood cells passing into the lumen or by pseudopodia of macrophages which lay outside the sinus. Cell traffic across the sinus wall was greatest in areas where blood cells were mixed with plasma. Congested spleens stored concentrated red cells in both sinuses and the reticular meshwork; contracted spleens were emptied of blood. The reticular meshwork may contract to assist trabecular and capsular smooth muscle in expelling stored red cells and effecting hemoconcentration.

Periarterial macrophage sheaths (ellipsoids) in cat spleen--an electron microscope study

Periarterial macrophage sheaths (PAMS), a term we introduce to replace "ellipsoids," surround arterial capillaries in the red pulp of the spleen and are major sites for clearance of blood-borne particles. PAMS and their arterial capillaries in cat spleens in various states of congestion and contraction were studied by transmission electron microscopy. Thorotrast, a colloidal suspension of thorium dioxide, was injected to label macrophages. A PAMS consisted of a fine meshwork of reticular cells and reticular fibers which held macrophages and formed a cylindrical sheath around an arterial capillary lying in its longitudinal axis. Some PAMS were spongy due to loosening of cell associations by plasma infiltration; others were tightly compressed. Blood cells were both free in the interstices of the PAMS and attached to macrophages. Reticular cells formed a closely applied but incomplete layer adventitial to the arterial capillary and extended branches which contributed to the meshwork. Small villous processes on the major branches of reticular cells approached each other, sometimes forming intercellular junctions, and fit into complementary indentations in the surfaces of macrophages and endothelial cells. Thin filaments within reticular cells filled the villous processes and formed a border beneath the plasmalemma; intermediate filaments ran through the centers of the branches. Reticular fibers lay between reticular cells. Basement membrane fabricated of the same material as reticular fibers lay between the endothelium and reticular cells. Macrophages contained Thorotrast and abundant debris of phagocytized cells and were joined by extensive interdigitation of micropseudopodia. Endothelial cells were long rods which lay parallel and were joined along their bases by interdigitating lateral processes. Intercellular junctions were present at some points, but at others lateral processes were everted to form open interendothelial slits through which blood cells could pass. Endothelial cells possessed great numbers of randomly oriented intermediate filaments and small patches of thin filaments scattered along the basal plasmalemma and in lateral processes. Thin filaments may function to attach cells to one another and to the basement membrane and may assist in closing interendothelial slits. We believe that the endothelium responds to changes in arterial blood pressure and blood flow. It stretches to allow dilatation and recoils, probably due to the intermediate filaments, squeezing blood cells through interendothelial slits.