Invariant chain-independent antigen presentation depends primarily upon the pool of newly synthesized MHC class II molecules

During biosynthesis, MHC class II molecules are diverted to endocytic compartments in which they bind antigenic peptides to be displayed on the surfaces of APC. For many Ags, the efficiency of class II presentation is enhanced by the intracellular association of class II with invariant chain (li), consistent with a role for newly synthesized class II molecules in Ag presentation. For a subset of Ags, however, efficient presentation does not require li. These Ags may also be bound by class II molecules en route to the cell surface. Alternatively, li-independent Ag presentation may utilize a pool of preexisting class II molecules that may gain access to endosomes following internalization from the cell surface. To examine the role of newly synthesized class II in the presentation of the li-independent Ag, RNase, we placed class II biosynthesis under the translational control of an iron response element. Chelation of iron from the media resulted in efficient diminution of class II synthesis and a marked decrease in the efficiency of RNase presentation. When compared with other cells expressing varying amounts of class II, we found that the ability to present RNase correlates with the level of class II biosynthesis and not with the level of class II surface expression. Because these cells internalize class II at a significant rate, we conclude that even in the absence of li, class II molecules can reach endocytic compartments containing antigenic peptides and they do so on their biosynthetic pathway.

Invariant chain-independent antigen presentation depends primarily upon the pool of newly synthesized MHC class II molecules

During biosynthesis, MHC class II molecules are diverted to endocytic compartments in which they bind antigenic peptides to be displayed on the surfaces of APC. For many Ags, the efficiency of class II presentation is enhanced by the intracellular association of class II with invariant chain (li), consistent with a role for newly synthesized class II molecules in Ag presentation. For a subset of Ags, however, efficient presentation does not require li. These Ags may also be bound by class II molecules en route to the cell surface. Alternatively, li-independent Ag presentation may utilize a pool of preexisting class II molecules that may gain access to endosomes following internalization from the cell surface. To examine the role of newly synthesized class II in the presentation of the li-independent Ag, RNase, we placed class II biosynthesis under the translational control of an iron response element. Chelation of iron from the media resulted in efficient diminution of class II synthesis and a marked decrease in the efficiency of RNase presentation. When compared with other cells expressing varying amounts of class II, we found that the ability to present RNase correlates with the level of class II biosynthesis and not with the level of class II surface expression. Because these cells internalize class II at a significant rate, we conclude that even in the absence of li, class II molecules can reach endocytic compartments containing antigenic peptides and they do so on their biosynthetic pathway.

Early, but not late, antiepileptic treatment reduces relapse of sound-induced seizures in the post-ischemic rat

Global ischemia was used to induce a sensitivity to sound-triggered generalized seizures in 24 male Long-Evans rats. All showed a generalized seizure when exposed to a 108 dB bell for 1 min. They were assigned randomly to 3 groups of 8, and received 30 additional sound exposures. The early treatment group was injected with valproate (200 mg/kg i.p) 1 h prior to each of the first 10 sound exposures. The late treatment group received the same treatment during the second set of 10 sound exposures after 10 sound exposures without treatment. The third group was untreated. Both early and late treated groups had a significant reduction in seizure incidence during the treatment period, i.e. both groups showed seizure control. However, in the late group seizures returned promptly when valproate treatment was discontinued, while the early group showed a sustained reduction in seizure susceptibility. Since this outcome corresponds to seizure remission, the findings of this study favor early treatment.

Management of aneurysmal subarachnoid hemorrhage

Treatment of ischemic deficits caused by vasospasm relies on enhancing cardiac output, inducing arterial hypertension, and expanding the intravascular volume in an attempt to improve CBF. Different treatment protocols exist from institution to institution to achieve these goals. The role of calcium-channel blockers now is well established. The newest focus on prevention of vasospasm includes tPA and a variety of anti-inflammatory drugs and potential neuroprotective drugs under research. Endovascular therapy for vasospasm has an increasing role in treating patients who are unable to tolerate induced hypertension or aggressive volume augmentation. We will return to our index case of the 63-year-old woman with SAH caused by an ACoA aneurysm to review some major management issues. After placing a ventriculostomy and slowly lowering ICP, the patient became alert and was fully oriented. She had aneurysm surgery on hospital day 2, with an uncomplicated immediate postoperative course. A Swan-Ganz catheter, placed for intraoperative monitoring, was kept in place and she was hydrated with 125 mL/hour of normal saline, achieving a PAWP of 10 to 16 mm Hg. Her mean arterial blood pressure without pharmacologic intervention was 95 to 110 mm Hg. She had continued clinical improvement with resolution of her left hemiparesis. On hospital day 5, her ventriculostomy was clamped because cerebrospinal fluid drainage was minimal. The following morning, the patient was arousable only to deep pain and her left side was flaccid. An emergent CT scan demonstrated no new hemorrhage, no increase in ventricular size, and no infarct. Vasospasm was considered the most likely cause. Hypertensive therapy was about to be initiated with a phenylephrine drip, but within an hour she was fully alert and moving all extremities equally. A search for other potential causes of neurologic decline was undertaken and revealed a phenytoin level of 5.5. It was thought that the patient most likely had had a seizure and that her clinical deterioration represented a postictal state. She received a bolus infusion of phenytoin. On hospital day 7, the patient became confused, insisting that her nurse was her son and ordering him out of her "apartment." Lower extremity weakness was detected. CT scan was unchanged. Phenylephrine was started but she developed precordial lead ST elevation and elevated cardiac enzymes. Topical nitrate therapy was initiated and phenylephrine was discontinued. The patient underwent emergent cerebral angiography, which demonstrated moderate to severe bilateral ACA spasm and moderate right MCA spasm.(ABSTRACT TRUNCATED AT 400 WORDS)

A Green's function method for heavy ion beam transport

The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of these methods. The first was the formulation of a closed-form solution as a multiple fragmentation perturbation series. The second was the effective summation of the closed-form solution through nonperturbative techniques. The nonperturbative methods have been recently extended to an inhomogeneous, two-layer transport media to simulate the lead scattering foil present in the Lawrence Berkeley Laboratories (LBL) biomedical beam line used for cancer therapy. Such inhomogeneous codes are necessary for astronaut shielding in space. The transport codes utilize the Langley Research Center atomic and nuclear database. Transport code and database evaluation are performed by comparison with experiments performed at the LBL Bevalac facility using 670 A MeV 20Ne and 600 A MeV 56Fe ion beams. The comparison with a time-of-flight and delta E detector measurement for the 20Ne beam and the plastic nuclear track detectors for 56Fe show agreement up to 35%-40% in water and aluminium targets, respectively.

Dynamics of thin filopodia during sea urchin gastrulation

At gastrulation in the sea urchin embryo, a dramatic rearrangement of cells establishes the three germ layers of the organism. Experiments have revealed a number of cell interactions at this stage that transfer patterning information from cell to cell. Of particular significance, primary mesenchyme cells, which are responsible for production of the embryonic skeleton, have been shown to obtain extensive positional information from the embryonic ectoderm. In the present study, high resolution Nomarski imaging reveals the presence of very thin filopodia (02-0.4 micron in diameter) extending from primary mesenchyme cells as well as from ectodermal and secondary mesenchyme cells. These thin filopodia sometimes extend to more than 80 microns in length and show average growth and retraction rates of nearly 10 microns/minute. The filopodia are highly dynamic, rapidly changing from extension to resorption; frequently, the resorption changes to resumption of assembly. The behavior, location and timing of active thin filopodial movements does not correlate with cell locomotion; instead, there is a strong correlation suggesting their involvement in cell-cell interactions associated with signaling and patterning at gastrulation. Nickel-treatment, which is known to create a patterning defect in skeletogenesis due to alterations in the ectoderm, alters the normal position-dependent differences in the thin filopodia. The effect is present in recombinant embryos in which the ectoderm alone was treated with nickel, and is absent in recombinant embryos in which only the primary mesenchyme cells were treated, suggesting that the filopodial length is substratum dependent rather than being primary mesenchyme cell autonomous. The thin filopodia provide a means by which cells can contact others several cell diameters away, suggesting that some of the signaling previously thought to be mediated by diffusible signals may instead by the result of direct receptor-ligand interactions between cell membranes.

Efficient internalization of MHC class II-invariant chain complexes is not sufficient for invariant chain proteolysis and class II antigen presentation

In Ag-presenting cells, MHC class II molecules bind antigenic peptides in endocytic compartments and transport them to the cell surface for presentation to CD4+ T cells. Newly synthesized class II alpha beta heterodimers associate with a third polypeptide, invariant chain (Ii), in the endoplasmic reticulum. This association may prevent class II molecules from binding peptides until they are transported to endocytic compartments where Ii is proteolyzed. Signals in the Ii cytosolic tail are believed to be responsible for the targeting of class II-Ii complexes to endocytic compartments, but it is unclear whether this targeting event occurs at the trans face of the Golgi or at the plasma membrane. In this report, we address whether the endosomal localization signal in the Ii cytosolic tail can be functionally substituted with a tyrosine-based signal for rapid internalization from the cell surface. A chimeric protein was generated in which the Ii cytosolic tail was replaced in its entirety with the cytosolic tail from transferrin receptor. In cells expressing this chimeric form of Ii, newly synthesized class II-Ii complexes travel rapidly to the cell surface and are internalized efficiently, but Ii proteolysis is delayed and class II Ag presentation is inhibited. These results suggest that targeting class II-Ii complexes to early/recycling endosomes from the cell surface does not in itself lead to Ii proteolysis; subsequent delivery to later endosomes may be required. The data suggest that signals for this targeting event may lie in residues 18 to 29 of the Ii cytosolic tail.

Efficient internalization of MHC class II-invariant chain complexes is not sufficient for invariant chain proteolysis and class II antigen presentation

In Ag-presenting cells, MHC class II molecules bind antigenic peptides in endocytic compartments and transport them to the cell surface for presentation to CD4+ T cells. Newly synthesized class II alpha beta heterodimers associate with a third polypeptide, invariant chain (Ii), in the endoplasmic reticulum. This association may prevent class II molecules from binding peptides until they are transported to endocytic compartments where Ii is proteolyzed. Signals in the Ii cytosolic tail are believed to be responsible for the targeting of class II-Ii complexes to endocytic compartments, but it is unclear whether this targeting event occurs at the trans face of the Golgi or at the plasma membrane. In this report, we address whether the endosomal localization signal in the Ii cytosolic tail can be functionally substituted with a tyrosine-based signal for rapid internalization from the cell surface. A chimeric protein was generated in which the Ii cytosolic tail was replaced in its entirety with the cytosolic tail from transferrin receptor. In cells expressing this chimeric form of Ii, newly synthesized class II-Ii complexes travel rapidly to the cell surface and are internalized efficiently, but Ii proteolysis is delayed and class II Ag presentation is inhibited. These results suggest that targeting class II-Ii complexes to early/recycling endosomes from the cell surface does not in itself lead to Ii proteolysis; subsequent delivery to later endosomes may be required. The data suggest that signals for this targeting event may lie in residues 18 to 29 of the Ii cytosolic tail.

Negative priming depends on ease of selection

Negative priming effects have been offered as evidence that distractor stimuli are identified. We conducted two experiments to determine if such effects occur even when it is easy to discriminate target from distractor stimuli. In Experiment 1, we found the usual negative priming effect when target and distractor positions varied from trial to trail, but not when these positions remained fixed. Experiment 2 extended these results to a situation where the ease of selection varied only in the prime display. These findings argue that irrelevant inputs can be filtered out prior to stimulus identification under certain circumstances and therefore pose problems for strict late selection theories.

Can mental rotation begin before perception finishes?

We conducted six experiments to determine if mental rotation can begin before perception finishes, as allowed by continuous flow models but not discrete state models of information processing. The results of Experiments 1-3 showed that the effect of shape discriminability on RT was underadditive with the effect of stimulus orientation, suggesting that mental rotation began before shape discrimination had finished and that the two processes overlapped in time. The results of experiments 4-6 indicated that mental rotation can overlap with color discriminations as well. In both sets of experiments, however, the amount of underadditivity tended to be much less than predicted by models allowing interference-free overlap. This suggests that mental rotation can overlap with perceptual analysis, contrary to fully discrete models, but that little rotation is carried out during this overlap due to interference between simultaneous discrimination and rotation processes.

De novo membranoproliferative glomerulonephritis in hepatitis C virus-infected renal allograft recipients

Hepatitis C virus (HCV) is the leading cause of non-A, non-B hepatitis among renal allograft recipients. We sought to identify and describe a proteinuric renal disease occurring in our HCV-infected renal transplant patients. Patients with proteinuria exceeding 1 g/day were identified from a cohort of 98 HCV-infected kidney recipients. Qualitative and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and restriction fragment-length polymorphism of the amplified RT-PCR product was performed to detect circulating HCV RNA, viral titer, and strain type, respectively. An immune complex nephritis (ICN) of the membranoproliferative pattern (MPGN) was found on five of eight biopsies. Two patients infected with the Hutch strain-type developed nephrotic-range proteinuria within three months posttransplant while the remaining three MPGN patients had been transplanted greater than 5 years prior to the onset of proteinuria. Testing for rheumatoid factors, cryoglobulins, hypocomplementemia, and circulating immune complexes failed to show a consistent pattern. Sucrose density gradient (SDG) equilibrium centrifugation was used to determine the buoyant-density of HCV virions from control (HCV-infected nonproteinuric recipients; n = 5) and nephrotic patients (n = 5). Whereas HCV virions from the control patients had a low buoyant density on sucrose gradients, a substantial percentage of the circulating HCV RNA from the MPGN patients was present in the high-density fractions in association with IgM and IgG. Treatment of the pooled high-density layers with NP40 followed by recentrifugation resulted in a shift of the HCV RNA to the medium-density layers. In conclusion, MPGN developed in five HCV-infected kidney recipients despite pharmacologic immunosuppression. Both the physicochemical properties of the HCV virions on SDG and their association with IgG and IgM in the high-density layers provide indirect evidence for the presence of circulating complexes of anti-HCV antibody and HCV antigen(s).

Efficient endosomal localization of major histocompatibility complex class II-invariant chain complexes requires multimerization of the invariant chain targeting sequence

During biosynthesis, MHC class II-invariant chain complexes are transported into endosomal compartments where invariant chain (Ii) is degraded and class II encounters antigenic peptides. One of the signals that determines this intracellular transport route has been localized to the cytosolic domain of Ii. Deletion of this signal disrupts endosomal targeting and results in the stable expression of class II-Ii complexes at the surface. In this paper we have examined the role of Ii trimerization on the generation of this endosomal localization signal. In L cell transfectants expressing class II and both wild type Ii and a truncated form of Ii that lacks this endosomal localization signal, Ii was found to form multimers which could contain both wild type and truncated Ii. The multimers were not large aggregates but were found to be discrete complexes, probably the nine molecule class II-Ii complex that has been observed in human B cells. The co-expression of truncated Ii allowed for cell surface expression of a subset of wild type Ii. This surface-expressed wild type Ii associated with truncated Ii in multimers at a 2:1 ratio, indicating that these trimers contain two truncated and one wild type Ii molecule. These data suggest a division in trafficking of Ii trimers: if two wild type Ii molecules are present, the complex is transported to and rapidly degraded in endosomes, whereas the presence of only one wild type Ii results in trafficking and expression of the heterotrimer on the cell surface. Following surface arrival, complexes containing only a single wild type Ii molecule are internalized more rapidly and have a shorter half-life than complexes containing only truncated Ii molecules. These data suggest that although a single Ii cytosolic domain can function as a plasma membrane internalization signal, multimerization of Ii is required for efficient Golgi complex to endosome targeting of class II-Ii complexes.

Does mental rotation require central mechanisms?

Four reaction time experiments examined the mental rotation process using a psychological refractory period paradigm. On each trial, participants made speeded responses to both a tone (S1) and a rotated letter (S2), presented with varying stimulus onset asynchronies (SOAs). If mental rotation of the stimulus letter can proceed while central mechanisms are busy with S1, then the effect of orientation should decrease substantially with decreasing SOA. Contrary to these predictions, the effect of orientation was nearly constant across SOAs, suggesting that mental rotation cannot effectively proceed without help from central mechanisms. These results support the conclusion that mental rotation requires access to a single-channel mechanism and must therefore be performed serially with other operations requiring the same mechanism.

B7-1 expression by a non-antigen presenting cell-derived tumor

The existence of a naturally occurring immunosurveillance against neoplastic cells is controversial. A difficulty with this concept is that tumor-specific antigen-reactive T cells would not be expected to become activated after encountering tumor cells, since T cells that bind to antigen in the absence of the costimulation provided by antigen-presenting cells may be inactivated. We studied a transgenic model of tumorigenesis where T cells reactive to a particular tumor-specific antigen are lost prior to the development of non-antigen-presenting cell-derived tumors; therefore, the tumors that develop are not subjected to immunosurveillance. We found that a tumor cell line derived from one such tumor expresses the T-cell costimulatory molecule B7-1, the expression of which is normally restricted to antigen-presenting cells. In addition, we found that several immortalized cell lines, which are nontumorigenic and thus have suffered only early genetic events in the tumorigenesis process, express B7. This suggests that a host cell can be induced to express surface B7-1 molecules after suffering an oncogenic insult, which might possibly be a primary mechanism of immunosurveillance against tumors.

Identification of a unique costimulatory activity for murine T helper 1 T cell clones

We have examined the ability of several class II-positive tumor cell transfectants to stimulate murine Th1 clones. Most of the transfectants failed to activate the Th1 clones and, in fact, induced Ag-specific anergy. However, we found that one tumor, a UV-induced fibrosarcoma (6130-VAR1), was capable of stimulating both cytokine production and proliferation in Th1 clones. We believe that 6130-VAR1 cells possess a unique costimulatory activity for the following reasons. First, these cells fail to express known costimulatory molecules including B7-1 and B7-2. Second, 6130-VAR1-mediated stimulation of Th1 clones was not blocked by anti-CD28 Fab or by CTLA4Ig, which suggests that members of the B7 family were not up-regulated during the course of stimulation and that activation does not occur via a CD28-dependent pathway. Third, 6130-VAR1 could provide costimulation when presented on a different surface than the class II/peptide ligand for the TCR. This last finding suggested that the activity on these cells was not simply an adhesion molecule that facilitated increased efficiency of T cell:MHC interactions. Finally, like B7-1 transfectants, stimulation by class II-positive 6130-VAR1 cells prevented the induction of anergy in the Th1 clones. Taken together, these results strongly suggest that 6130-VAR1 expresses a unique costimulatory activity (VAM-1) that, like B7-1, can promote T cell activation and prevent anergy induction.

Response complexity and precue interval effects on the lateralized readiness potential

Fundamental properties of an important new tool in cognitive electrophysiology, the lateralized readiness potential (LRP), were examined in two experiments. Experiment 1 resolved an apparent inconsistency in the literature by demonstrating that this response-specific lateralization is larger preceding complex then preceding simple finger movements. In Experiment 2, the foveally presented precue, which indicated hand of response, preceded the go/no-go stimulus by 0, 100, 300, or 1,400 ms. Analyses of LRP latency indicated that hand-specific preparation began earlier with longer foreperiods but was temporally linked to the reaction stimulus as well as the precue. Although the degree of lateralization did not predict reaction speed in either study, a nonlateralized, response-locked negativity was larger prior to faster reactions.

Neuropsychological detection of dementia: an overview of the neuropsychological component of the Canadian Study of Health and Aging

As part of the Canadian Study of Health and Aging (CSHA), a battery of neuropsychological measures was administered to 1879 participants. Participants who received neuropsychological evaluations were selected from an age-stratified random sample on the basis of scores on a cognitive screening tool, the Modified Mini-Mental State Examination (3MS). Seventy-five percent of the sample seen for neuropsychological evaluation scored between 50 and 77 on the 3MS and 25% of the sample scored 78 or over. This paper provides a descriptive summary of the methodological basis of the neuropsychological component of the CSHA. The findings indicated that differences existed between participants administered the battery in English or French in terms of refusal rates and diagnoses of dementia. Cursory examination of the utility of the battery indicated that the battery was tolerated well by both the participants and the psychologists involved with the study and that measures of memory functioning were central to diagnostic decision-making. The relations between neuropsychological, preliminary medical and consensus diagnoses were examined and indicated that neuropsychological information influenced diagnostic decision-making. The neuropsychology component of the CSHA is a rich source of information on persons aged 65 years and older in Canada.

Mechanisms of immune tolerance induction through the thymic expression of a peripheral tissue-specific protein

A major process through which the immune system becomes tolerant to self proteins involves the deletion of self reactive cells in the thymus. However, T cells reactive to peripheral tissue-specific proteins can escape this deletion and become tolerized in the periphery by a variety of mechanisms. We report here, contrary to expectation, that the pancreas-specific protein, elastase I, is also expressed at a low level in the thymus, and that this thymic expression contributes to tolerance induction. To study the mechanism of this tolerance induction, we utilized a double transgenic mouse model. In these mice the expression of a model protein, SV40 T antigen, is directed by the elastase I promoter and hence parallels elastase I expression in the pancreas and thymus. These mice were crossed with mice transgenic for a TCR specific for T antigen, so the majority of thymocytes and T cells in these mice express the transgene. In double transgenic mice we find that thymic expression of T antigen results in anergic thymocytes which also show a reduction of Th1 activity with no decrease in Th2 activity. These functional characteristics persist in peripheral T cells, but there is also a depletion in the number of T antigen reactive T cells in lymph nodes. Chimeras were constructed which directly demonstrated that the thymus is the site of tolerance induction and that the tolerizing element is thymic epithelium. We propose that the loss of Th1 activity as a consequence of the thymic epithelium being encountered by tissue-specific proteins results in the functional tolerization of CTL in vivo, despite the fact that CTL are fully functional in vitro. In this way autoimmune destruction is contained. Thymic expression of peripheral proteins may therefore be an additional way in which tolerance to peripheral proteins can be achieved.

Identification of a unique costimulatory activity for murine T helper 1 T cell clones

We have examined the ability of several class II-positive tumor cell transfectants to stimulate murine Th1 clones. Most of the transfectants failed to activate the Th1 clones and, in fact, induced Ag-specific anergy. However, we found that one tumor, a UV-induced fibrosarcoma (6130-VAR1), was capable of stimulating both cytokine production and proliferation in Th1 clones. We believe that 6130-VAR1 cells possess a unique costimulatory activity for the following reasons. First, these cells fail to express known costimulatory molecules including B7-1 and B7-2. Second, 6130-VAR1-mediated stimulation of Th1 clones was not blocked by anti-CD28 Fab or by CTLA4Ig, which suggests that members of the B7 family were not up-regulated during the course of stimulation and that activation does not occur via a CD28-dependent pathway. Third, 6130-VAR1 could provide costimulation when presented on a different surface than the class II/peptide ligand for the TCR. This last finding suggested that the activity on these cells was not simply an adhesion molecule that facilitated increased efficiency of T cell:MHC interactions. Finally, like B7-1 transfectants, stimulation by class II-positive 6130-VAR1 cells prevented the induction of anergy in the Th1 clones. Taken together, these results strongly suggest that 6130-VAR1 expresses a unique costimulatory activity (VAM-1) that, like B7-1, can promote T cell activation and prevent anergy induction.

Acute graft loss secondary to necrotizing vasculitis. Evidence for cytokine-mediated Shwartzman reaction in clinical kidney transplantation

A small number of kidney transplant recipients abruptly lose function secondary to acute renal artery or vein thrombosis or more rarely a form of necrotizing vasculitis. We report a group of four kidney transplant recipients who lost renal function and share the following features: (1) diabetes (type I, insulin-dependent diabetes mellitus, type II or steroid-induced); (2) abrupt change/loss of renal function; (3) a concomitant clinical event (fever, viral symptoms, menometrorrhagia, viremia, bacteremia); (4) severe necrotizing vasculitis with hemorrhagic necrosis on histopathology; (5) patent renal artery and vein at time of transplant nephrectomy (i.e., no vascular thrombosis); and (6) high levels of peripheral serum gamma-IFN 1-5 days before transplant nephrectomy (467 +/- 175 pg/ml) compared with that of patients experiencing severe rejection (8.4 +/- 3.7 pg/ml) (P < 0.002). These data support the concept of a cytokine (IFN-gamma)-mediated accelerated inflammatory response resulting in graft loss from necrotizing vasculitis--the clinical equivalent of an organ-specific Shwartzman reaction.