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Biomedical subjects

C Watts

Publications and source records attributed to C Watts.

At least 127 records · Page 7Linked to original sources
PubMed1992

Constitutive endocytosis and recycling of major histocompatibility complex class II glycoproteins in human B-lymphoblastoid cells.

Cleavable cell surface radiolabelling reagents were used to measure the endocytosis and recycling of class II major histocompatibility complex (MHC) glycoproteins in human B-lymphoblastoid cells. It is shown that mature class II alpha beta dimers on the cell surface are constitutively endocytosed and that recycling can be demonstrated even from small endosomal pools. Endocytosis was blocked when cellular ATP levels were depleted or when clathrin polymerization was inhibited, implicating clathrin-coated pits in the endocytic process. Taken together with earlier studies, these results suggest that mature class II MHC molecules are constitutively endocytosed and recycled from acidic peripheral endosomes which may enhance their capacity to bind and present T cell epitopes which do not require processing.

Adenosine Triphosphate↗
PubMed1992

Primary prevention of catastrophic injury.

Motor vehicle crashes are a leading cause of injury and death until age 45. Efforts to prevent these injuries have largely followed the dictates of the public health movement focusing on interventions for entire communities or regulatory statutes. Individual interventions, more congruent with traditional psychological approaches, have been rare. This article argues that a blending of these two approaches is warranted. Evaluation of prevention programs should focus on multiple levels including the individual, the community, and regulatory processes. Identification of subgroups of adolescents and young adults with unique psychological and behavioral dispositions regarding injury must be paired with realistic interventions of adequate duration.

Accidents, Traffic↗
PubMed1992

National Head and Spinal Cord Injury Prevention Program of the American Association of Neurological Surgeons and the Congress of Neurological Surgeons.

Organized neurosurgery has developed and promoted a national educational program for adolescents to reduce the number of head and spinal cord injuries sustained by this group of young people. The program has been adopted widely, with over 1,000,000 teenagers exposed to it since its inception in 1986. Preliminary data suggest that the program has had a favorable impact on the knowledge and attitudes of young people regarding head and spinal cord injuries, risk-taking behavior, and incidence of injuries.

Child↗
PubMed1991

Processed antigen binds to newly synthesized MHC class II molecules in antigen-specific B lymphocytes.

We describe the direct detection of radiolabeled antigen fragments bound to class II MHC molecules following immunoglobulin-mediated endocytosis and processing of native antigen in B lymphoblastoid cells. Tris-Tricine SDS gels revealed six distinct iodinated processing products that could be detected on class II MHC 1 hr after antigen endocytosis and persisted for at least 20 hr. These physiological processed antigen-class II complexes were remarkably stable, as judged by the fact that class II alpha beta dimers, which remain associated in SDS, became labeled with the same set of processed peptides. Using a lectin-binding assay, we show that these physiological processing products bind to the newly maturing population of MHC molecules rather than binding to the preexisting cell surface population; in contrast, an exogenous peptide binds predominantly to the latter population. A direct T cell-independent assay for processed peptide-MHC complex formation should facilitate additional studies on the exogenous antigen processing pathway.

Antibodies, Monoclonal↗
PubMed1990

Cycling of cell-surface MHC glycoproteins through primaquine-sensitive intracellular compartments.

Class II major histocompatibility complex (MHC) glycoproteins associate with peptides derived from material endocytosed by antigen-presenting cells and processed along the endocytotic pathway. No consensus exists as to what extent class II molecules themselves are endocytosed and it is not known whether endocytosed MHC class II molecules can be recycled again to the cell surface--an itinerary which might allow a single cell-surface MHC molecule to associate with different peptides during its lifetime. We now show by using new cleavable labelling reagents that class II and class I MHC on B lymphoblastoid cells are continually endocytosed and recycled to the cell surface. The intracellular pool size is normally kept small by efficient recycling, but in the presence of primaquine the rate of recycling is slowed, thereby increasing the size of this pool substantially. On removal of the amine, the intracellular population recycles rapidly to restore the original distribution. These results reveal a cycle that might explain the rapid binding and turnover of some peptide/class II MHC complexes and the exchange of pre-existing for new peptides observed in living cells.

Antibodies, Monoclonal↗
PubMed1990

Endocytosis, intracellular trafficking, and processing of membrane IgG and monovalent antigen/membrane IgG complexes in B lymphocytes.

Human B lymphoblastoid cell lines specific for tetanus toxin/toxoid were used in our earlier studies to demonstrate the rapid endocytosis of monovalent Ag and its processing, as a complex with mIgG. Here we show that the mIgGR for Ag is endocytosed in the presence or absence of Ag and that at any given time about 60% of this recycling pool of membrane (m) Ig is inside the cell. During the earliest detectable stages of Ag processing a high proportion of Ag fragments resolved on SDS gels were bound to intact mIg. However, at later times, as fragmented Ag accumulated, the fragments were precipitable only with antibodies against the Fab region of mIgG indicating proteolytic fragmentation of this receptor. Fractionation of cell homogenates on self-forming Percoll gradients revealed that at least two compartments are involved in Ag processing: a low density endosome compartment and a dense "late endosome"/lysosomal compartment. The spectrum of Ag fragments observed in each fraction differed: fragments produced at later times during processing were detected only in the late endosome/lysomal fraction whereas the earliest observed fragments were found both in this fraction and in the low density fractions. Monovalent Ag/mIgG complexes appear to have an increased probability, compared to unoccupied mIgG, of targeting to proteolytically active compartments leading to processing of the Ag/mIg complex and to accelerated degradation of the mIgG.

Antigen-Antibody Complex↗
PubMed1990

The antigen processing pathway in B lymphocytes.

Monovalent antigen bound to membrane immunoglobulin on human B lymphoblastoid cells is endocytosed through coated pits and passes sequentially from a site which actively recycles membrane to the cell surface and then to a proteolytically active processing site. A high affinity of immunoglobulin for antigen precludes antigen dissociation following endocytosis and results in the processing of an antigen/Ig complex yielding an epitope-specific pattern of processing. Processing of the immunoglobulin also occurs and is enhanced by occupancy with monovalent antigen.

Antigens↗
PubMed1990

Use of traction in cervical spine fractures during interhospital transfer by aircraft.

Despite significant improvement in the organization and function of the nation's emergency medical services and the increasing sophistication of initial providers of critical care, there has apparently been no reduction in the incidence of neurological deficits suffered by patients with unstable cervical spine injuries during management prior to intervention by the spine surgeon. In analyzing the techniques used to stabilize patients with suspected unstable cervical spine injuries during this phase, we conclude that present standard techniques are either insufficient or potentially destabilizing. We have developed a system that will permit the use of cervical traction, applied with a halter or the standard Gardner-Wells tongs, during the prehospital phase of management of patients with cervical spine injuries. Based on our experience with the system, we recommend that patients with such injuries be stabilized with skeletal traction when transferred between hospitals by air ambulance. Logic permits consideration of the concept even earlier in the prehospital phase of management and in ground ambulances.

Adult↗
PubMed1990

High-order multifetal gestation--management and outcome.

During the period 1975-1989, 11 high-order (quadruplet or more) multifetal gestations reaching the second trimester were treated in our department. All pregnancies resulted from ovulation induction therapy. Premature contractions occurred in all cases. Two women delivered stillborn quadruplets vaginally at 25 and 26 weeks' gestation. Nine women had cesarean deliveries at 28-35 weeks; one fetus was stillborn and two of the 39 live-born infants died. Twenty-nine (74%) weighed less than 1500 g and 16 (41%) were below the tenth percentile for gestational age. Thirty infants have been followed for at least 2 years, corrected for gestational age; 21 (70%) are developing normally, two are severely handicapped with both cerebral palsy and mental retardation, four have mild motor delay, and three have mild motor and mental delay.

Adult↗
PubMed1989

Epitope-directed processing of specific antigen by B lymphocytes.

Proteolytic processing of specific antigen was studied using Epstein Barr virus transformed B-lymphoblastoid cells expressing membrane IgG against tetanus toxin. As previously reported (Watts, C., and H.W. Davidson. 1988. EMBO (Eur. Mol. Biol. Organ.) J. 7:1937-1945), receptor-mediated endocytosis of monovalent antigen bound at 0 degrees C began immediately upon shifting the cells to 37 degrees C. In contrast, degradation of antigen, assessed either by the release of acid-soluble radiolabel into the incubation medium, or by SDS-PAGE analysis of total cell-associated antigen, proceeded after a lag of 10-20 min. Degradation was abolished by exposure of the cells to metabolic inhibitors, or by incubation at 20 degrees C, and inhibited in a dose-dependent fashion by chloroquine and by the lysosomal protease inhibitors leupeptin, E-64, and pepstatin A. Analysis of the cell-associated radiolabel by SDS-PAGE and autoradiography after incubations at 37 degrees C revealed the time-dependent generation of distinct antigen fragments. Virtually quantitative immunoprecipitation of these fragments was obtained using a monoclonal anti-human IgG antibody, indicating that the antigen/mIg complex is the initial substrate for processing. We show that the pattern of fragmentation observed varies from one B cell line to another (a) depending on the epitope through which the antigen is bound and endocytosed and (b) depending on whether additional epitopes in the antigen are complexed with anti-tetanus Fabs. The implications of these results for the presentation of major histocompatibility complex restricted antigen fragments, and for intracellular trafficking of ligand/receptor complexes are discussed.

Antigen-Presenting Cells↗
PubMed1989

Distinct endocytotic pathways in epidermal growth factor-stimulated human carcinoma A431 cells.

Addition of EGF to human epidermoid carcinoma A431 cells increases the rate of fluid-phase pinocytosis 6-10-fold as measured by horseradish peroxidase uptake (Haigler, H.T., J. A. McKanna, and S. Cohen. 1979. J. Cell Biol. 83:82-90). We show here that in the absence of extracellular Na+ or in the presence of amiloride the stimulation of pinocytosis by EGF is substantially reduced. Amiloride had no effect on the endocytosis of EGF itself or of transferrin, demonstrating that the receptor-mediated endocytotic pathway operated normally under conditions that blocked stimulated pinocytosis. Amiloride blocked EGF-stimulated pinocytosis in both HCO3(-)-containing and HCO3(-)-free media. The EGF-stimulated pinocytotic activity can frequently be localized to areas of the cell where membrane spreading and ruffling are taking place. These results demonstrate that (a) EGF induces a distinct amiloride-sensitive endocytotic pathway on A431 cells; (b) occupied EGF receptors do not utilize this pathway for their own entry; (c) endocytosis of occupied EGF receptors is not in itself sufficient to stimulate pinocytosis.

Amiloride↗
PubMed1988

Endocytosis and recycling of specific antigen by human B cell lines.

Human B cell lines expressing membrane immunoglobulin specific for tetanus toxoid/toxin were used to study the receptor-mediated endocytosis of antigen. Monovalent antigen, initially bound to cell surface immunoglobulin at 0 degree C, was rapidly endocytosed upon warming the cells to 37 degrees C. The kinetics of endocytosis of antigen were independent of the number of occupied binding sites and indicated a half-life for antigen on the cell surface of 8.5 min. Endocytosis of antigen apparently ceased after approximately 15 min at 37 degrees C, although some 40-50% remained on the cell surface at this time. We show, using biotinylated antigen and an avidin detection assay, that this is due to recycling of antigen to the cell surface. By labelling the antigen on the cell surface with Fabs against different epitopes we show that antigen continues to be endocytosed for at least 1 h after the initial rapid phase of endocytosis, again indicating that there must be recycling of immunoglobulin/antigen complexes. As a consequence of the stable interaction between antigen and membrane immunoglobulin, the capacity of the cells to accumulate antigen was limited when the synthesis of membrane immunoglobulin was blocked; under these conditions only 2-3 times as much antigen was endocytosed and degraded when antigen was supplied continuously over a 4-h period at 37 degrees C as could be bound to the cells at 0 degree C. These results reveal a rapid and efficient pathway for the endocytosis and recycling of monovalent antigen in B cells.

Antigen-Antibody Complex↗