Humoral immune response to human aortic valve homografts

The humoral response to homograft valves in humans is largely unknown. The anti-human lymphocyte antigen (HLA) antibody production, specificity, and immunoglobulin class were examined sequentially in 73 patients undergoing aortic valve replacement. In addition, the long-term production of antibodies was examined in a cross-sectional study of 160 patients at periods varying from 1 to 15 years postoperatively. Human lymphocyte antigen antibodies were produced in 17 of 30 antibiotic-sterilized homografts (56%) and in 15 of 15 "homovital" homograft recipients, compared with 6 of the 28 control xenograft recipients (21%) (p < 0.001). The HLA antibodies were immunoglobulin G in all 15 homovital homografts, in 11 of 17 antibiotic-sterilized homografts, and in four of the six xenograft cases. Human lymphocyte antigen specificities could be assigned to the antibodies in 21 cases. In 10 of 11 cases in which donor HLA typing data were available, the antibodies detected were directed against donor HLA class I antigens. Of six possible determinants of HLA antibody production, the type of homograft valve implanted (homovital or antibiotic sterilized) correlated with antibody formation. In the cross-sectional study, 66 of the 85 homovital homograft recipients tested for HLA antibodies after 1 year were found to have antibodies, compared with 29 of 75 antibiotic-sterilized homograft recipients (p = 0.00003). We conclude that homografts appear to stimulate a strong donor HLA-specific antibody response, particularly of the immunoglobulin G class. This is most common in homovital valve recipients. These antibodies can persist for 15 years after operation. The clinical significance of this response requires further investigation.

Switches in expression of Plasmodium falciparum var genes correlate with changes in antigenic and cytoadherent phenotypes of infected erythrocytes

Plasmodium falciparum expresses on the host erythrocyte surface clonally variant antigens and ligands that mediate adherence to endothelial receptors. Both are central to pathogenesis, since they allow chronicity of infection and lead to concentration of infected erythrocytes in cerebral vessels. Here we show that expression of variant antigenic determinants is correlated with expression of individual members of a large, multigene family named var. Each var gene contains copies of a motif that has been previously shown to bind diverse host receptors; expression of a specific var gene correlated with binding to ICAM-1. Thus, our findings are consistent with the involvement of var genes in antigenic variation and binding to endothelium.

Recurrent intrapulmonary malignant small cell tumor of the thoracopulmonary region with metastasis to the oral cavity: review of literature and case report

Malignant small cell tumor of the thoracopulmonary region (MSCT) was first described in 1979 and has been referred to as the Askin tumor. This malignant neoplasm is a member of the peripheral primitive neuroectodermal tumor (PPNET) family and typically involves the periosteum, soft tissue, and extrapulmonary tissue of the thoracic wall. MSCT may also involve the lung parenchyma by local extension or may arise de novo in peripheral lung tissue. Local recurrence, abdominal involvement by tumor extravasation across the diaphragm, and skeletal metastatic disease are relatively common. However, metastasis to the head and neck region and in particular to the oral cavity is extremely rare. We present a recurrent intrapulmonary MSCT with metastasis to the oral cavity in an adolescent Hispanic boy, and review the literature regarding this member of the PPNET family. Differentiation from neuroblastoma may be made based on immunoreactivity for beta 2 microglobulin and HBA71 and lack of immunoreactivity for chromogranin in PPNET and MSCT. Ultrastructural features commonly seen in MSCT and PPNET are round to ovoid tumor cells with occasional cytoplasmic processes with relatively few pleomorphic dense core granules. These tumors lack the gangliocytic and Schwann cell differentiation that is characteristic of neuroblastoma. MSCT and PPNET have a common reciprocal cytogenetic translocation [t(11;22)q(24;q12)], which is shared with Ewing's sarcoma. Prognosis in MSCT is quite dismal, with a 2-year survival of 38% and a 6-year survival of only 14%.

Fibrous dysplasia: a case report

Fibrous dysplasia is a benign fibro-osseous disorder that often affects both the maxilla and mandible. The dentist, therefore, is often the first person to identify and diagnose the disease. This article focuses on the pathology, diagnosis, clinical course, and treatment of this complex problem. A case report demonstrates the multidisciplinary approach to the management of this disease entity.

Characterization of class I MHC folding intermediates and their disparate interactions with peptide and beta 2-microglobulin

Newly synthesized class I heavy chains achieve domain structure using disulfide bonds, assemble with beta-2 microglobulin (beta 2m), and bind peptide ligand to complete the trimeric complex. Although each of these initial events is thought to be critical for class I folding, their sequential order and effect on class I structure are unknown. Using mAb specific for distinct conformations of H-2Ld and Lq, we have defined folding intermediates of class I molecules. We show here that non-peptide-associated forms of Ld or Lq, detected by mAb 64-3-7 and designated L alt, lack numerous conformational epitopes surrounding their ligand binding sites. These results support the notion that L alt molecules have an open conformation. Interestingly, a significant proportion of L alt molecules were detected in association with beta 2m and these L alt/beta 2m heterodimers were preferentially folded by peptide in cell lysates. These findings indicate that class I heavy chain/beta 2m association can precede ligand binding and that peptide is probably the limiting factor for completion of the Ld/beta 2m/peptide trimeric complex in vivo. The characteristics of L alt molecules were investigated further by ascertaining the disulfide bond status of these molecules and their association with beta 2m and peptide. Treatment of cells with dithiothreitol (DTT), a membrane-permeable reducing agent, demonstrated that L alt molecules constitute a heterogeneous population including reduced, partially reduced and native class I molecules. Furthermore, partially reduced Ld alt molecules, in a cell line expressing a mutant Ld molecule lacking the alpha 2 domain disulfide bond, accumulated intracellularly, were not beta 2m-associated and displayed marginal peptide-induced folding in vitro. In accordance with this latter finding, peptide was found to preferentially convert fully disulfide-bonded forms of Ld alt to conformed Ld. Thus, we propose that intrachain disulfide bond formation precedes the association of class I heavy chain with beta 2m and peptide, and that disulfide bond formation is required for efficient assembly, ligand binding and folding of the class I heavy chain.

Computer screening for early detection of melanoma--is there a future?

Computer image analysis in the study of pigmented lesions is critically examined and discussed in the light of the current published data. The potential for objective analysis by computers as a possible screening aid for the inexperienced clinician is discussed. The future for this technology is exciting if handled with care.

Pre-transplant anti-epithelial cell antibodies and graft failure after single lung transplantation

Eighty-five patients undergoing single lung transplantation have been studied to determine the presence of anti-epithelial cell antibodies (AECA) prior to transplantation using the human lung carcinoma epithelial cell line A549 in a microcytotoxicity assay. In addition, 29 healthy volunteers were also assayed for the presence of AECA. Twenty-seven of the 85 recipients exhibited AECA prior to transplantation compared to none of the 29 control subjects (p = 0.0001). Actuarial graft survival at 1 year was 78% for the AECA negative group compared to 56% for AECA positive recipients (p = 0.01). No correlation was seen between the presence of AECA and graft rejection as determined by transbronchial biopsy. However, there was an association between AECA and post-transplant infection (p = NS) where 16 (64%) of the AECA positive recipients had postoperative infection episodes compared to 25 (47%) of the negative recipients. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Western blotting was also performed for 68 of the recipients and antibody reactivity was detected in 22 patients compared to 26 patients exhibiting AECA detectable by microcytotoxicity. The presence of AECA demonstrable by Western blotting did not correlate with graft survival, rejection or infection. In conclusion, AECA detectable prior to single lung transplantation are associated with a decrease in graft survival and with postoperative infections.

Placement of a permanent cystostomy catheter to relieve urine outflow obstruction in dogs with transitional cell carcinoma

Permanent cystostomy catheters were placed in 7 dogs to relieve urine outflow obstruction from presumed transitional cell carcinoma of the bladder trigone and urethra. The catheters were easily managed at home by the owners. Complications were minimal. The most frequent complication was urinary tract infection. Two owners complained of difficulty in draining the bladder 1 week before euthanasia of their dogs. The primary reason for euthanasia of all dogs was progression of the tumor. Survival times of these dogs were similar to those previously reported for dogs with transitional cell carcinoma involving the bladder and urethra, irrespective of treatment. Placement of a permanent cystostomy catheter should be considered in dogs with transitional cell carcinoma associated with urine outflow obstruction when, owing to the dog's condition or the owner's preference, radical surgery or other treatment is not an option.

Definition of TCR recognition sites on Ld-tum- complexes

The P911 variant of the P815 mastocytoma was shown by Lurquin et al. (Cell 58:293, 1989) to elicit rapid tumor rejection in a syngeneic host. This rejection was mediated by Ld-restricted cytotoxic T lymphocytes (CTL) for which targets could be sensitized by the synthetic peptide designated tum- (P91A-.12-24). In a previous study, T cell clones specific for Ld-tum- complexes displayed very restricted TCR usage and a characteristic TCR motif in the V alpha CDR3 region, predicted to interact with peptide. However, in contrast to the majority of Ld peptide ligands that are nonamers, the tum- peptide is a 13-mer and its sequence does not fit the Ld binding motif. Thus, to define shorter versions of the tum- 13-mer and residues involved in TCR recognition, nonamer derivatives were synthesized and compared in several different binding and functional assays. From these comparisons, the peptide TQNHRALDL was found to be the optimal nonamer. CTL recognition of Ala-substituted analogues of this peptide indicated that the His and Arg residues at positions 4 and 5 are important for TCR contact. We propose that these basic residues of the tum- peptide interact with the previously defined acidic residues in the CDR3 region of several TCR known to recognize Ld-tum- complexes.

Fatal carbon dioxide embolism complicating attempted laparoscopic cholecystectomy--case report and literature review

Laparoscopic cholecystectomy has become the surgical procedure of choice for individuals with symptomatic gallbladder disease. The procedure has gained popularity among surgeons and patients because of inconspicuous abdominal incisions/scars, less postoperative pain, shorter hospitalization, and reduced medical costs. Bile duct, vascular, and gastrointestinal iatrogenic injuries are major complications. We describe the case of a 50-year-old woman who died of CO2 embolism during elective laparoscopic cholecystectomy for symptomatic cholelithiasis. With the patient under general anesthesia, a 1.5 cm incision was made just below the umbilicus, and a pneumoperitoneum was created by CO2 insufflation with a pneumoperitoneum (modified Veress) needle. Immediately, she experienced a cardiopulmonary arrest and could not be resuscitated. At autopsy, air bubbles were admixed with blood in the epicardial veins and leptomeningeal blood vessels. A triangular 0.1 cm perforation in the left common iliac vein had been created by the pneumoperitoneum needle. A pneumoperitoneum is required for laparoscopy and CO2 is the most commonly used gas. Carbon dioxide is highly soluble in blood and fairly innocuous to the peritoneum. Small amounts absorbed into the circulation cause slight increases in arterial and alveolar CO2 and in central venous pressure. When CO2 enters the venous circulation through iatrogenically opened vascular channels, catastrophic and potentially fatal hemodynamic and respiratory compromise may result.

Identification of opaque-2 genotypes in segregating populations of Quality Protein Maize by analysis of restriction fragment length polymorphisms

Quality Protein Maize (QPM) is a name given to genetically modified opaque-2 maize with hard endosperm. The opaque-2 mutation conditions a reduction in the amount of zein seed storage protein; zeins are deficient in the essential amino acids lysine and tryptophan, and mutant seed have a higher nutritional value. To utilize the potential of opaque-2 maize, elite inbreds can be converted to o2/o2 forms and subsequently to hard endosperm opaque-2. Since opaque-2 is recessive and endosperm specific, conventional backcross procedures to convert elite inbreds to opaque-2 forms are inefficient. To alleviate this problem, a marker-assisted selection procedure was developed for the Texas A&M University Quality Protein Maize breeding program. Hybridization of an O2 cDNA probe to blots of DNA from plants carrying O2 and o2 alleles showed that restriction fragment length polymorphisms (RFLPs) exist between the W64A o2 allele and O2 alleles of Mo17 and TX5855 inbred lines. To identify the opaque2 genotypes in segregating populations, an RFLP marker assay combining the O2 cDNA probe and HindIII-digestion of genomic DNA was developed. The effectiveness of the O2 RFLP marker assay was tested under field conditions using F2 and backcross populations of several hard endosperm opaque-2 lines. A comparison of the genotypes identified by RFLP analysis with the seed phenotypes of the next generation indicated that this procedure is accurate and can be used for identifying O2/O2, O2/o2, and o2/o2 genotypes of individual juvenile plants in breeding populations.

What child is this? What interval was that? Familiar tunes and music perception in novice listeners

In the laboratory, musical novices often seem insensitive even to basic structural elements of music (octaves, intervals, etc.), undermining long-held theories of music perception, and threatening to leave current theories applicable only to experts. Consequently it is important to demonstrate novices' basic listening competence where possible. Two experiments examined the perception of musical intervals (minor thirds, major thirds and perfect fourths) by musical novices. Subjects received either standard instructions or familiar folk-tune labels to aid performance. The folk-tune labels greatly improved identification performance, producing expert-caliber performance by some musically inexperienced subjects. The effectiveness of the folk-tune manipulation was much more limited in a difficult discrimination task. The results suggest that novices do have some basic competence when assayed appropriately, and that familiar musical tokens may be a critical element in such assays. Larger implications of the role of familiarity in novices' competence are discussed, including those that relate to music cognition and aesthetics.

The selective antiproliferative effects of alpha-tocopheryl hemisuccinate and cholesteryl hemisuccinate on murine leukemia cells result from the action of the intact compounds

In the present study we have established that the antitumor activity of alpha-tocopheryl succinate (TS, vitamin E succinate) and cholesteryl succinate (CS) result from the action of the intact TS and CS compounds and not from the release of alpha-tocopherol, cholesterol, or succinate. We report that treatment of murine leukemia cell lines C1498 (myeloid) and L1210 (lymphocytic), with the tris salts of TS or CS, but not alpha-tocopherol and tris succinate or cholesterol and tris succinate, significantly inhibit the growth of these tumor cells and significantly enhance doxorubicin-induced tumor cell kill in a similar fashion. In contrast, the treatments mentioned above did not adversely affect the growth of murine normal bone marrow cells (colony-forming unit-granulocyte-macrophage). In fact, colony-forming unit granulocyte-macrophage cell growth was stimulated by exposure to CS and TS (as well as their ether analogues) at concentrations above 100 microM. Furthermore, pretreatment of colony-forming unit granulocyte-macrophage cells with TS or CS appears to protect these normal cells from the lethal effect of doxorubicin exposure. Selective inhibition of leukemia cell proliferation (identical to that noted for CS and TS) was also observed following the treatment of cells with the nonhydrolyzable ether forms of CS (cholesteryloxybutyric acid) and TS (alpha-tocopheryloxybutyric acid). These findings suggest that TS, alpha-tocopheryloxybutyric acid, CS, and cholesteryloxybutyric acid may prove clinically useful as selective antitumor agents when administered alone or in combination with doxorubicin by a route that ensures tissue accumulation of the intact compound.

Inhibition of cholinesterase activity by tetrahydroaminoacridine and the hemisuccinate esters of tocopherol and cholesterol

The anticholinesterase properties of tetrahydroaminoacridine (THA, Tacrine), alpha-tocopheryl hemisuccinate (TS), and cholesteryl hemisuccinate (CS), given alone and in combination, were examined in vitro. Results from these studies indicate that: [1] THA is a potent inhibitor of acetylcholinesterase (AChE, IC50 of 0.40 microM) and butyrylcholinesterase (BChE, IC50 of 0.10 microM) with greatest inhibitory activity towards BChE; [2] TS and CS are weak inhibitors of BChE (IC50 of 100 microM and 168 microM, respectively) but potent inhibitors of ACHE (IC50 of 1.73 microM and 0.79 microM, respectively); [3] both TS and CS treatment in combination with THA significantly increased THA's anticholinesterase activity. The percentage AChE inhibition observed with this combination was often significantly greater than the sum of the individual values (synergistic). The addition of 0.5 microM CS or TS to an ACHE preparation reduced THA's IC50 value from 0.40 microM or 0.18 microM, respectively [4]; inhibition of AChE by THA, TS and CS are mixed non-competitive while THA inhibition of BChE is mixed non-competitive and TS and CS inhibition of BChE are simple non-competitive; and [5] inhibition of cholinesterases by TS and CS occurs immediately (50 to 75%), during the first 30 min of incubation (25 to 50%) and is dependent on the anionic charged portion of the molecule. In conclusion, our experimental data indicate that TS and CS are potent inhibitors of AChE activity and significantly potentiate the anticholinesterase activity of THA. Such potent and synergistic inhibition of AChE suggest that TS or CS, alone and in combination with THA, may prove beneficial in the treatment of organophosphate poisoning and Alzheimer's disease.

Reactions of Ugandan antisera with peptides encoded by V3 loop epitopes of human immunodeficiency virus type 1

The specificities of antibodies reacting with peptides encoded by V3 loop apical epitopes were determined for sera from 230 seropositive Ugandans, including asymptomatic persons and AIDS patients, sampled between 1986 and 1992. Most (71%) of the sera reacted with the peptide encoded by HIV-MN, 59% reacted with a peptide containing a consensus sequence for Ugandan variants of the HIV-1 global subtype A (referred to as the Uganda A consensus), 59% reacted with a peptide containing a consensus sequence for Ugandan variants of the global subtype D (the Uganda D consensus); 19% of the sera also reacted with peptides encoded by the divergent Ugandan variant U31. There was no obvious correlation between the specificities of antibody binding and the V3 loop sequence of the corresponding virus isolate or provirus. Competitive inhibition and antibody adsorption experiments indicated that the MN peptide, the Uganda A consensus peptide, the Uganda D consensus peptide, and the U31 peptide were recognized by different sets of antibodies. Eighteen percent of the sera from AIDS patients and 26% of the sera from asymptomatic persons were monospecific for one of the MN, Uganda A, or Uganda D peptides. Whereas all except one of the singly reactive AIDS sera were specific for MN, 39% of the singly reactive asymptomatic sera were specific for MN, 39% for the Uganda A peptide, and 21% for the Uganda D peptides. We conclude that analysis of the specificities of antibodies against the V3 loop epitopes in sera from asymptomatic persons could provide useful epidemiological data about the prevalence of viral subtypes within a population.

Correcting torsional deformities with Ilizarov's apparatus

Patients undergoing limb lengthening with circular fixators often have rotational deformities requiring correction as well. At the end of lengthening, special rotation constructs are added to the Ilizarov frame to correct the rotational deformity. Unfortunately, the bone is usually eccentrically positioned in the rings, leading to secondary translational deformities after derotation. A trigonometric equation can predict the amount of inadvertent translation (t) that occurs with a given amount of derotation. Factors in this equation include the distance from the center of the ring to the outer edge of bone (r) and the amount of planned derotation (theta): t = (r sin theta)/sin (90 -theta/2). This sinusoidal function for derotation angles of less than 45 degrees can be approximated as a simple equation: t = 0.017 theta r. Armed with this information, the surgeon may calculate how much translation will be induced by the derotation maneuver. If the amount of predicted translation is deemed significant, then a more complex derotation frame with outriggers can be constructed to change the center of rotation to the middle of the eccentric bone. Alternatively, the translation induced by rotation can later be corrected with a translation construct.

Physical activity patterns among adults in Georgia: results from the 1990 Behavioral Risk Factor Surveillance System

Regular physical activity increases a person's ability to perform daily activities more efficiently, reduces the risk of specific chronic diseases, including coronary artery disease, and lowers death rates in general. The Healthy People 2000 Physical Activity and Fitness Objectives underscored the importance of monitoring and tracking the prevalence of physical activity and fitness in the United States population for the purpose of planning, implementing, and evaluating efforts to improve the public's physical activity habits. This report examines the prevalence of self-reported leisure-time physical activity (LTPA) among southeastern adults aged 18 years and older living in the state of Georgia. Using data from the 1990 Behavioral Risk Factor Surveillance System (BRFSS) surveys from Georgia, we describe the LTPA patterns of Georgia adults aged 18 years and older. A total of 1,723 adults were interviewed during 1990. Results show the following: women are less active than men, blacks are less active than whites, persons of lower socioeconomic status (SES) are less active than those of higher SES, and older adults are less active than younger adults. These results suggest that a more concerted effort needs to be made in promoting physical activity for women, persons of lower SES, and older adults.

Overexpression of apolipoprotein CII causes hypertriglyceridemia in transgenic mice

We have generated transgenic mice expressing the human apolipoprotein CII (apoCII) gene under the transcriptional control of the human cytochrome P-450 IA1 (CYPIA1) promoter. Human apoCII transgenic (HuCIITg) mice exhibited significant basal expression of the transgene (plasma apoCII level = 26.1 +/- 4 mg/dl) and showed further induction of transgene expression after treatment with beta-naphthoflavone. Unexpectedly, HuCIITg mice were hypertriglyceridemic and human apoCII levels correlated strongly to triglyceride levels (R = 0.89, P < 0.0001). Triglyceride levels (mg/dl +/- SEM) were elevated compared to controls in both the fed (804 +/- 113 vs 146 +/- 18, P < 0.001) and fasted (273 +/- 39 vs 61 +/- 4, P < 0.001) states. HuCIITg mice accumulated triglyceride-rich very low density lipoproteins (VLDL) with an increased apoC/apoE ratio. Tracer kinetic studies indicated delayed clearance of VLDL-triglyceride, and studies using Triton inhibition of VLDL clearance showed no increase in VLDL production. Plasma from these mice activated mouse lipoprotein lipase normally and radiolabeled VLDL were normally hydrolyzed. However, HuCIITg VLDL showed markedly decreased binding to heparin-Sepharose, suggesting that apoCII-rich, apoE-poor lipoprotein may be less accessible to cell surface lipases or receptors within their glycosaminoglycan matrices. HuCIITg mice are a promising model of hypertriglyceridemia that suggests a more complex role for apoCII in the metabolism of plasma triglycerides.

Retransplantation in heart-lung recipients with obliterative bronchiolitis

Obliterative bronchiolitis remains the leading cause of morbidity and mortality in long-term survivors after heart-lung transplantation. Despite enhanced immunosuppressive therapy, a significant number of patients progress to end-stage respiratory failure, leaving retransplantation as the only potential therapeutic option. Between October 1986 and August 1990, 25 heart-lung recipients (mean age 22 +/- 2 years) underwent repeat heart-lung transplantation at an average of 21 months after their first procedure. Twenty-one patients (83%) were ventilator dependent at the time of retransplantation. The Kaplan-Meier survival at 1, 6, 12, and 24 months was 52%, 33%, 25%, and 25%, respectively. Postoperative complications included bleeding, multisystem organ failure, and infection. Obliterative bronchiolitis resulted in death or graft failure in three patients between 12 and 36 months after the second transplantation. Five patients were currently alive at the time this article was written, with a median follow-up of 54 months. Three were in New York Heart Association class I, and two had obliterative bronchiolitis with class III symptoms. Recently, we investigated the role of single lung retransplantation in nine heart-lung recipients (mean age 23 +/- 3 years). The mean interval between procedures was 36 months, and eight patients (88%) were ventilator dependent. The Kaplan-Meier survival at 1, 6, 12, and 24 months was 89%, 67%, 67%, and 50%, respectively. We observed significantly less perioperative morbidity in this group. Five patients were alive (median follow-up 20 months); four were in New York Heart Association class I or II, and one was in New York Heart Association class III with recurrent obliterative bronchiolitis. We did not have enough patients to perform multivariate survival analysis. Survival curve comparisons with the use of the Wilcoxon test did show that the absence of performed antibodies in the recipient (panel reactive antibody frequency less than 10%) was associated with significantly improved survival after retransplantation. We also noted trends for improved survival in patients who had retransplantation at least 18 months after their original transplantation and in patients with negative preoperative sputum cultures. Retransplantation is a high-risk procedure that can result in rehabilitation in otherwise incapacitated patients. Single lung retransplantation appears to be the preferred option in carefully selected patients.

Model for the in vivo assembly of nascent Ld class I molecules and for the expression of unfolded Ld molecules at the cell surface

To characterize the process of class I assembly and maturation, we have studied the Ld molecule of the mouse. Previous studies have shown that a significant proportion of intracellular and surface Ld molecules can be detected in an alternative conformation designated Ldalt1. Nascent Ldalt molecules are non-peptide ligand associated and are weakly associated with beta 2-microglobulin (beta 2m). Unexpectedly, when monoclonal antibodies were added directly to the lysis buffer, significant amounts of Ldalt/beta 2m heterodimer were detected, suggesting that beta 2m association is not necessarily sufficient to induce Ld conformation. By contrast, addition of peptide to cell lysates rapidly induced the folding of beta 2m-associated Ldalt to conformed Ld. Furthermore, the time course and dynamics of this conversion correlated precisely with peptide binding to Ld. The precursor-product relationship of Ldalt and conformed Ld was also visualized in vivo by pulse-chase analysis of BALB/c splenocytes. To investigate the factors that regulate intracellular transport of class I molecules, expression of Ld was studied in the peptide transport-deficient cell line, RMA.S-Ld, and in beta 2m-/- splenocytes. In contrast to wild-type cell lines, both Ldalt and conformed Ld are poorly expressed at the cell surface of RMA.S-Ld and beta 2m-/- splenocytes. Therefore, surface expression of Ldalt is dependent upon the concomitant expression of conformed Ld molecules. To determine whether surface Ldalt molecules can result from melting of conformed Ld molecules, surface Ld molecules were loaded with several different known Ld peptide ligands. Complexes of Ld with different ligands were found to have dramatically disparate surface half-lives. Importantly, the Ld peptide complexes that turned over the most rapidly resulted in the most gain in surface Ldalt, implying that peptide dissociation can induce the accumulation of nonconformed Ld heavy chains at the cell surface.

Binding of peptides lacking consensus anchor residue alters H-2Ld serologic recognition

CTL recognize class I MHC/peptide complexes on the surface of target cells. Crystallographic and serologic data have indicated that peptide ligands can influence the conformation of class I molecules and hence T cell recognition. How the binding of peptides with disparate sequence motifs affects the conformation of distinct regions within a class I molecule remains unknown. A series of site-directed mutants of the murine class I molecule H-2Ld was studied to address this question. These mutants were generated by in vitro mutagenesis and used to map the serologic epitopes recognized by a panel of Ld-reactive mAb. The influence of six different ligands on serologic recognition by these mAb was then examined. Of 12 mAb tested, only one, B22/249, was found to be significantly influenced by the bound peptide. Peptide discrimination by B22/249 was observed at the cell surface and in immunoprecipitates of Ld after incubation with two of the six ligands. The two peptides that caused suboptimal B22/249 recognition of Ld/peptide lack a proline at position 2, which is present in the other four peptides and has previously been defined as an anchor residue for Ld ligands. The epitope on Ld detected by mAb B22/249 includes residues 63 to 70 on the alpha 1 domain helix. Two of these residues are in pocket B, which computer modeling predicts to be in contact with the second residue of Ld-binding peptides. Therefore, these data imply that a mAb to a class I molecule can distinguish peptides with different motifs, possibly reflecting peptide-dependent conformational changes in the class I molecule.