Presentation of viral antigen to class I major histocompatibility complex-restricted cytotoxic T lymphocyte. Recognition of an immunodominant influenza hemagglutinin site by cytotoxic T lymphocyte is independent of the position of the site in the hemagglutinin translation product.

Class I major histocompatibility complex (MHC) restricted T lymphocytes preferentially recognize fragments of polypeptides processed through a nonendosomal presentation pathway. At present the intracellular compartment(s) in which polypeptide fragmentation occurs and factors which influence the formation of an antigenic epitope are not well understood. To assess the role of residues flanking an antigenic site in the generation of the antigenic moiety recognized by class I MHC restricted T lymphocytes we have moved the coding sequence for an immunodominant H-2Kd restricted site on the influenza A/JAPAN/57 hemagglutinin (residues 202-221) by site-directed mutagenesis to six different positions along the coding sequence of the hemagglutinin gene. We have found that all six classes of mutants are recognized by MHC class I restricted T cells as efficiently as the wild type hemagglutinin gene product. Thus neither N-terminal to C-terminal position within the translation product nor sequences flanking the antigenic site influence processing.

The requirement for proteasome activity class I major histocompatibility complex antigen presentation is dictated by the length of preprocessed antigen.

Accumulating evidence has implicated the proteasome in the processing of protein along the major histocompatibility complex (MHC) class I presentation pathway. The availability of potent proteasome inhibitors provides an opportunity to examine the role of proteasome function in antigen presentation by MHC class I molecules to CD8+ cytotoxic T lymphocytes (CTLs). We have investigated the processing and presenting of antigenic epitopes from influenza hemagglutinin in target cells treated with the inhibitor of proteasome activity MG132. In the absence of proteasome activity, the processing and presentation of the full-length hemagglutinin was abolished, suggesting the requirement for proteasome function in the processing and presentation of the hemagglutinin glycoprotein. Epitope-containing translation products as short as 21 amino acids when expressed in target cells required proteasome activity for processing and presentation of the hemagglutin epitope to CTLs. However, when endogenous peptides of 17 amino acids or shorter were expressed in target cells, the processing and presentation of epitopes contained in these peptides were insensitive to the proteasome inhibitor. Our results support the hypothesis that proteasome activity is required for the generation of peptides presented by MHC class I molecules and that the requirement for proteasome activity is dependent on the size of the translation product expressed in the target cell. The implications of these findings are discussed.

CD8+ T cell recognition of an endogenously processed epitope is regulated primarily by residues within the epitope.

Cytotoxic T lymphocytes (CTL) recognize short antigenic peptides associated with cell surface class I major histocompatibility complex (MHC) molecules. This association presumably occurs between newly synthesized class I MHC molecules and peptide fragments in a pre-Golgi compartment. Little is known about the factors that regulate the formation of these antigenic peptide fragments within the cell. To examine the role of residues within a core epitope and in the flanking sequences for the generation and presentation of the newly synthesized peptide fragment recognized by CD8+ CTL, we have mutagenized the coding sequence for the CTL epitope spanning residues 202-221 in the influenza A/Japan/57 hemagglutinin (HA). In this study over 60 substitution mutations in the epitope were tested for their effects on target cell sensitization using a cytoplasmic viral expression system. The HA202-221 site contains two overlapping subsites defined by CTL clones 11-1 and 40-2. Mutations in HA residues 204-213 or residues 210-219 often abolished target cell lysis by CTL clones 11-1 and 40-2, respectively. Although residues outside the core epitope did not usually affect the ability to be lysed by CTL clones, substitution of a Gly residue for Val-214 abolished lysis by clone 11-1. These data suggest that residues within a site that affect MHC binding and T cell receptor recognition appear to play the predominant role in dictating the formation of the antigenic complex recognized by CD8+ CTL, and therefore the antigenicity of the protein antigen presented to CD8+ T cells. Most alterations in residues flanking the endogenously expressed epitope do not appreciably affect the generation and recognition of the site.

Interaction between complement receptor gC1qR and hepatitis C virus core protein inhibits T-lymphocyte proliferation.

Hepatitis C virus (HCV) is an important human pathogen that is remarkably efficient at establishing persistent infection. The HCV core protein is the first protein expressed during the early phase of HCV infection. Our previous work demonstrated that the HCV core protein suppresses host immune responses, including anti-viral cytotoxic T-lymphocyte responses in a murine model. To investigate the mechanism of HCV core-mediated immunosuppression, we searched for host proteins capable of associating with the core protein using a yeast two-hybrid system. Using the core protein as bait, we screened a human T cell-enriched expression library and identified a gene encoding the gC1q receptor (gC1qR). C1q is a ligand of gC1qR and is involved in the early host defense against infection. Like C1q, HCV core can inhibit T-cell proliferative responses in vitro. This core-induced anti-T-cell proliferation is reversed by addition of anti-gC1qR Ab in a T-cell proliferation assay. Furthermore, biochemical analysis of the interaction between core and gC1qR indicates that HCV core binds the region spanning amino acids 188 to 259 of gC1qR, a site distinct from the binding region of C1q. The inhibition of T-cell responsiveness by HCV core may have important implications for HCV persistence in humans.

Alveolar epithelial cell chemokine expression triggered by antigen-specific cytolytic CD8(+) T cell recognition.

CD8(+) T lymphocyte responses are a critical arm of the immune response to respiratory virus infection and may play a role in the pathogenesis of interstitial lung disease. We have shown that CD8(+) T cells induce significant lung injury in the absence of virus infection by adoptive transfer into mice with alveolar expression of a viral transgene. The injury is characterized by the parenchymal infiltration of host cells, primarily macrophages, which correlates with physiologic deficits in transgenic animals. CD8(+) T cell-mediated lung injury can occur in the absence of perforin and Fas expression as long as TNF-alpha is available. Here, we show that the effect of TNF-alpha expressed by CD8(+) T cells is mediated not exclusively by cytotoxicity, but also through the activation of alveolar target cells and their expression of inflammatory mediators. CD8(+) T cell recognition of alveolar cells in vitro triggered monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) expression in the targets, which was mediated by TNF-alpha. Antigen-dependent alveolar MCP-1 expression was observed in vivo as early as 3 hours after CD8(+) T cell transfer and depended upon TNF-R1 expression in transgenic recipients. MCP-1 neutralization significantly reduced parenchymal infiltration after T cell transfer. We conclude that alveolar epithelial cells actively participate in the inflammation and lung injury associated with CD8(+) T cell recognition of alveolar antigens.

Conserved elements in the 3' untranslated region of flavivirus RNAs and potential cyclization sequences.

We have isolated a cDNA clone after reverse transcription of the genomic RNA of Asibi yellow fever virus whose structure suggests it was formed by self-priming from a 3'-terminal hairpin of 87 nucleotides in the genomic RNA. We have also isolated a clone from cDNA made to Murray Valley encephalitis virus RNA that also appears to have arisen by self-priming from a 3'-terminal structure very similar or identical to that of yellow fever. In addition, 3'-terminal sequencing of the S1 strain of dengue 2 RNA shows that this RNA is also capable of forming a 3'-terminal hairpin of 79 nucleotides. Furthermore, we have identified two 20-nucleotide sequence elements which are present in the 3' untranslated region of all three viruses; one of these sequence elements is repeated in Murray Valley encephalitis and dengue 2 RNA but not in yellow fever RNA. In all three viruses, which represent the three major serological subgroups of the mosquito-borne flaviviruses, the 3'-proximal conserved sequence element, which is found immediately adjacent to the potential 3'-terminal hairpin, is complementary to another conserved domain near the 5' end of the viral RNAs, suggesting that flavivirus RNAs can cyclize (calculated delta G less than -11 kcal; 1 kcal = 4.184 kJ).

Hepatitis C virus: immunosuppression by complement regulatory pathway.

Hepatitis C virus (HCV) infection in humans is almost invariably associated with viral persistence and chronic hepatitis. HCV-induced chronic hepatitis is a major risk factor for the development of hepatocellular carcinoma. The high incidence of HCV persistence suggests that this virus has evolved one or more mechanisms to evade and possibly suppress host immune responses. To understand the mechanism(s) involved in the establishment of HCV persistence, we have identified an HCV core protein as an immunomodulatory molecule to suppress host immune response. We have further determined a molecular mechanism of HCV core-mediated immune suppression by searching for a potential host protein(s) capable of associating with the HCV core protein. Interestingly, the Clq complement receptor, gC1qR, can bind to the HCV core. Clq is a ligand of gClqR and is involved in the early defense against viral infection as well as regulation of adaptive immune response. Similar to Clq, the HCV core can inhibit human T-lymphocyte proliferative response through its interaction with the gC1qR. It implicates that HCV core/gClqR-induced immune suppression may play a critical role in the establishment of persistent infection.

An elastic pouch operation for large retinal tears.

An episcleral pouch operation that uses Dacron-reinforced silicone sheeting for the patch and silicone sponge pellets for the stuffing has been used to extend the localized radial buckling technique to retinal detachments that are caused by breaks that span a circumferential arc between 40 degrees and 70 degrees. Nineteen of 20 retinal detachments responded favorably to the operation, 14 without drainage of subretinal fluid. When the pouch was extended circumferentially to apply to detachments caused by breaks greater than 70 degrees, it failed in six of seven patients because a radial configuration could no longer be maintained. The substitution of transparent silicone sheeting for donor sclera facilitates the fitting and stuffing of the pouch.

Infection after sponge implantation for scleral buckling.

In one series of 900 explant scleral buckling procedures, 31 had to be removed over seven years because of contamination. Of 1,000 explants from a parallel series, 27 had to be removed. In the second series, requirement of a sterile conjunctiva preoperatively and the use of prophylactic antibiotics postoperatively did not significantly reduce the rate of infection.

Atrial diverticula in severe hydrocephalus.

Massive ventricular dilatation causes stretching and dehiscence of the fornix with formation of unilateral or bilateral pial pulsion diverticula of the inferior medial wall of the atrium. Enlargement of the pial pouch creates a dramatic subarachnoid cyst that may herniate downward through the incisura into the lateral mesencephalic, precentral cerebellar, and superior vermian cisterns where it displaces the brain stem, vermis, and fourth ventricle. Lateral ventricular diverticula may be identified and distinguished from the dilated fourth ventricle and dilated suprapineal recess, with which they are so commonly confused, when all of the following signs are apparent on computed tomography (CT): (1) marked unilateral or bilateral atrial dilatation; (2) focal dehiscence of the medial atrial wall; (3) ipsilateral shortening of the tentorial band in axial section; (4) focal defect in the tentorial band in coronal section; (5) draping of the medial atrial wall over the free margin of tentorium, with continuity of cerebrospinal fluid density around the edge of tentorium in axial and/or coronal sections; (6) bowing of the crus (or crura) of fornix; (7) separation of fornix from splenium, with visualization of the hernia ostium; (8) asymmetrical position of the choroid plexi, which attach to and define the lateral borders of the fornices; (9) contralateral displacement of the internal cerebral veins; and (10) septa separating diverticulum from third ventricle

Traumatic bilateral ophthalmic artery aneurysms: a case report.

A case of bilateral ophthalmic artery aneurysm of traumatic origin is discussed. The patient presented with progressive loss of vision, memory deficit, and expressive aphasia. A computed tomographic scan revealed enhancing lesions near the region of the optic chiasm. The diagnosis of cerebral aneurysm was confirmed by cerebral angiography. At operation, bilateral ophthalmic artery aneurysms were successfully clipped.

Scalp and calvarial masses of infants and children.

Review of 70 children presenting with a solitary nontraumatic lump on the head revealed that 61% of the lesions were dermoid tumor, 9% were cephalhematoma deformans, 7% were eosinophilic granuloma, and 4% were occult meningoceles and encephaloceles. Most of the dermoid cysts occurred along sutural lines, but some did not. One of the eosinophilic granulomas was located over the sagittal suture. Seventeen per cent of the "lumps" had significant intracranial extension. An additional 20% of the lumps extended intracranially, but only to the dura mater. Work-up of these lesions should include initial plain skull roentgenograms to assess multiplicity and appropriate computed tomographic scans to assess possible intracranial extension.

Factors influencing posttraumatic seizures in children.

The ideal treatment of children with head trauma would include prevention of posttraumatic seizures. Ninety-two of 937 children with head injuries (9.8%) experienced posttraumatic seizures. In 94.5% of these patients (87 of 92), seizures developed within the first 24 hours after injury. Three children convulsed between 24 hours and 7 days, but only 2 children developed seizures after the 1st week. Factors found to influence the likelihood of seizures included severe head injury (GCS, 3 to 8), diffuse cerebral edema, and acute subdural hematoma (P less than 0.001). Seizures occurred in 35% of severely head-injured children compared to 5.1% with minor head injury (P less than 0.001). A less significant correlation (P less than 0.1) was noted between seizures and open, depressed skull fractures. We found no significant correlation between seizure occurrence and numerous other factors including age, sex, fracture location and type (other than open, depressed fractures), parenchymal injuries, fixed neurological deficits, and cranial operation. Based on our observations, we recommend the prophylactic use of anticonvulsants in children at higher risk for posttraumatic seizures: those with diffuse cerebral edema, acute subdural hematoma, open, depressed skull fracture with parenchymal damage, or severe head injury (GCS less than or equal to 8).

Intraneural hematoma of the sciatic nerve. Case report.

A case of an encapsulated organizing hematoma of the sciatic nerve is reported. Hemorrhage-induced neuropathy as a complication of anticoagulant therapy, leukemia, hemophilia, and other bleeding diatheses has been frequently reported. While trauma is the most common etiology of a hemorrhagic neuropathy, actual hematoma formation beneath the epineurium is very rare.

Evasion of host immune surveillance by hepatitis C virus: potential roles in viral persistence.

Hepatitis C virus (HCV) is a major human pathogen that causes mild to severe liver disease worldwide. This positive strand RNA virus is remarkably efficient at establishing chronic infections. In order for a noncytopathic virus such as HCV to persist, the virus must escape immune recognition or evade host immune surveillance. Immune escape via the hypervariable region of the E2 envelope protein has been postulated as one mechanism for HCV persistent infection. Such hypervariability within the E2 protein may be under selective pressure from protective B cell or T cell responses and be able to escape immune recognition by rapid mutation of antigenic site. In addition to antigenic variation, HCV may also suppress immune response, leading to dampening of cellular immunity. This is supported by recent studies in our laboratory demonstrating that the HCV core protein can suppress host immune responses to vaccinia virus by downregulating viral specific cytotoxic T lymphocyte (CTL) responses and cytokine production. An understanding of the mechanisms behind HCV persistence will provide a basis for the rational design of vaccines and novel therapeutic agents targeting human HCV infection.

Brain herniation and space-occupying lesions eroding the tegmen tympani.

Technological advances in neuroradiology and the development of skull base surgery in neurotology have improved diagnosis and management of lesions eroding the tegmen tympani. The diagnosis of brain hernia is to be suspected in patients with a history of complicated chronic ear surgery and a slowly developing pulsatile mass with CSF leak. Patients are best evaluated in the upright position, with an otomicroscope and by magnetic resonance imaging (MRI). Over 6 years, our group has treated seven patients with eight space-occupying lesions eroding the tegmen. Five of the lesions were repaired with a temporalis muscle flap, 2 with fascia and bone, and 1 with Marlex. A review of new technology in the diagnosis of brain hernia and a modification of previous techniques is given.

Management of the child with severe brain injury.

The pathophysiology and clinical management of acute brain injury in infancy and childhood are presented using acute traumatic brain injury as a model. The principles of stabilization, transport, and intensive care management are critically reviewed.

Open myelomeningocele.

This article defines open myelomeningocele and describes its development in the embryo. The anatomic features of the neural placode, pia-arachnoid, and dorsal versus ventral roots are well described. The surgical technique and prenatal and postnatal care are detailed. Anomalies associated with open myelomeningocele are also described. The concept of a team approach to treating children with myelomeningocele and their families is addressed.

Risk factors of intracranial pressure monitoring in children with fiberoptic devices: a critical review.

BACKGROUND: Intracranial pressure (ICP) monitoring has become standard in the management of severe head injuries. A variety of monitoring techniques and devices are available, each with advantages and disadvantages; however there have been few studies in the pediatric population. METHODS: To study the risk factors, efficacy, and complication rate of fiberoptic ICP monitoring we studied 98 consecutive children with severe head injuries over a 2-year period. The average patient age was 9 years and most had an initial Childrens Coma Score (CCS) of 8 or less. The monitoring devices were placed in frontal parenchyma of all children and no prophylactic antibiotics were used. All fiberoptic catheter tips were cultured upon removal. RESULTS: The average duration of ICP monitoring was 7 days; the usual range was 3-15 days, with the exception of one patient who underwent monitoring for 40 days. No complications occurred during insertion of the ICP monitors. Catheter tip cultures were positive for Staphylococcus epidermidis in 7% of the children, but none developed clinical features of CNS infection. The hospital location of placement or duration of ICP monitoring did not affect the rate of catheter tips with positive cultures. There was a 13% mechanical failure rate of the fiberoptic device. CONCLUSIONS: We conclude that fiberoptic ICP monitoring is safe and effective; however, there is a relatively low mechanical failure rate. Infection in uncommon despite prolonged use and there is little risk of complications associated with placement of this monitor.

Hypopituitarism and chorioretinopathy in two siblings.

Two male siblings with chorioretinopathy and pituitary dysfunction (CPD) were found to have empty sellas on CT scan. Extensive ophthalmological and endocrinological investigation revealed the absence of gonadotrophins in both brothers and growth hormone deficiency in one. ACTH, TSH, and posterior pituitary function were normal. Karyotyping in one brother revealed a 46XY complement. Ophthalmological evaluation of three other siblings and both parents revealed normal vision and no evidence of retinopathy. The brothers represent two additional examples of CPD syndrome, suggesting a genetic etiology for this syndrome complex. The empty sellas present add another facet to the central nervous system disorders found in CPD syndrome.