Naturally processed HLA class II peptides reveal highly conserved immunogenic flanking region sequence preferences that reflect antigen processing rather than peptide-MHC interactions

MHC class II heterodimers bind peptides 12-20 aa in length. The peptide flanking residues (PFRs) of these ligands extend from a central binding core consisting of nine amino acids. Increasing evidence suggests that the PFRs can alter the immunogenicity of T cell epitopes. We have previously noted that eluted peptide pool sequence data derived from an MHC class II Ag reflect patterns of enrichment not only in the core binding region but also in the PFRS: We sought to distinguish whether these enrichments reflect cellular processes or direct MHC-peptide interactions. Using the multiple sclerosis-associated allele HLA-DR2, pool sequence data from naturally processed ligands were compared with the patterns of enrichment obtained by binding semicombinatorial peptide libraries to empty HLA-DR2 molecules. Naturally processed ligands revealed patterns of enrichment reflecting both the binding motif of HLA-DR2 (position (P)1, aliphatic; P4, bulky hydrophobic; and P6, polar) as well as the nonbound flanking regions, including acidic residues at the N terminus and basic residues at the C terminus. These PFR enrichments were independent of MHC-peptide interactions. Further studies revealed similar patterns in nine other HLA alleles, with the C-terminal basic residues being as highly conserved as the previously described N-terminal prolines of MHC class II ligands. There is evidence that addition of C-terminal basic PFRs to known peptide epitopes is able to enhance both processing as well as T cell activation. Recognition of these allele-transcending patterns in the PFRs may prove useful in epitope identification and vaccine design.

Identification of MUC1 proteolytic cleavage sites in vivo

Mucins are high molecular weight glycoproteins that provide a protective layer on epithelial surfaces and are involved in cell-cell interactions, signaling, and metastasis. The identification of several membrane-tethered mucins, including MUC1, MUC3, MUC4, and MUC12, has incited interest in the processing of these mucins and the mechanisms that govern their release from the cell surface. MUC1 consists of an extracellular subunit and a membrane-associated subunit. The two moieties are produced from a single precursor polypeptide by an early proteolytic cleavage event but remain associated throughout intracellular processing and transport to the cell surface. We identified the MUC1 proteolytic cleavage site and showed it to be identical in pancreas and colon cell lines and not to be influenced by the presence of heavily glycosylated tandem repeats. The MUC1 cleavage site shows homology with sequences in other cell-surface-associated proteins and may represent a common mechanism for processing of these molecules.

A binocular site for contrast-modulated masking

Contrast-modulated (CM) gratings, composed of two luminance-modulated sinusoids of similar spatial frequency, mask the detection of test sinusoids at the difference frequency. However, the mechanism underlying masking by CM gratings remains poorly understood. In this paper, we aimed to determine whether the masking of 1 cycle deg(-1) LM test gratings by a 1 cycle deg(-1) beat (formed from a pair of carriers at 8 and 9 cycles deg(-1)) occurs in monocular channels or after the site of binocular combination, or both. Threshold elevations for the detection of a 1 cycle deg(-1) test grating were obtained for a number of stimulus conditions, including: (1) dichoptic CM (both 8 and 9 cycles deg(-1) mask components presented to one eye, with the 1 cycle deg(-1) test grating to the other); (2) dichoptic variant (8 and 9 cycles deg(-1) mask gratings presented to separate eyes, with the 1 cycle deg(-1) test grating presented to one eye); (3) binocular CM (all mask and test gratings presented to both eyes). As a control, masking magnitude was also measured for LM mask gratings of similar frequency (1 cycle deg(-1)) and effective contrast (3%) to that of the beat. For both LM and CM masks, the dichoptic condition yielded threshold elevations that were similar or greater than the binocular condition. When 8 and 9 cycles deg(-1) mask components were presented to separate eyes (the dichoptic variant condition), no beat pattern was visible and no elevations in detection threshold occurred. The results demonstrate that, like LM masking, detection of a target in the presence of a CM mask does not involve purely monocular mechanisms. Further, that the site of CM masking must occur beyond the stage at which monocular matching for stereopsis takes place. This is consistent with other studies which suggest that dichoptic masking is contingent on stereo matching, and thus occurs relatively late in the hierarchy of binocular visual processing.

Molecular effects of calcium binding mutations in Marfan syndrome depend on domain context

Mutations in the human fibrillin-1 (FBN-1) gene cause Marfan syndrome (MFS), an autosomal dominant disease of connective tissue. Fibrillin-1, a 350 kDa extracellular calcium binding protein, is a major structural component of 10-12 nm microfibrils and consists predominantly of two repeated module types: the calcium binding epidermal growth factor-like (cbEGF) domain and the transforming growth factor beta1 binding protein-like (TB) domain. A group of reported FBN-1 mutations is predicted to reduce calcium binding to cbEGF domains by removal of a side chain ligand for calcium. These mutations occur in two protein domain contexts, either in a cbEGF preceded by a TB domain or in a cbEGF preceded by another cbEGF domain. In this study we have used three proteases to probe structural changes caused by an N2144S MFS calcium binding mutation in a TB6-cbEGF32 and a cbEGF32-33 domain pair, and an N2183S mutation in the cbEGF32-33 pair. N-terminal sequence analysis of domain pairs digested in the presence and absence of calcium show that: (i) domain interactions between TB6 and cbEGF32 are calcium independent, despite the presence of a calcium binding site in cbEGF32; (ii) domain interactions between cbEGF32 and cbEGF33 are calcium dependent; and (iii) an N-->S mutation causes increased proteolytic susceptibility only when located in cbEGF33, consistent with a key role for interdomain calcium binding in rigidifying cbEGF domain linkages. These data demonstrate for the first time that the structural consequences of calcium binding mutations in fibrillin-1 cbEGF domains can be influenced by domain context.

Comparing contrast-modulated and luminance-modulated masking: effects of spatial frequency and phase

The masking of a sinusoidal test grating by contrast-modulated (CM) gratings could, in principle, be attributable to the presence of a distortion product, injected into the stimulus during some nonlinear transformation at an early level of visual processing (e.g. Nachmias, 1989 Vision Research 29 137-142). If so, CM gratings and luminance-modulated (LM) gratings of similar effective contrast and spatial frequency should mask the detection of sinusoids in a similar fashion. We compared the effects of masking by 1 cycle deg-1 CM gratings [both simple beats (8 + 9 cycles deg-1) and amplitude-modulated gratings (8 + 9 + 10 cycles deg-1)], with those of masking by 1 cycle deg-1 LM gratings of low contrast. We found that: (i) CM and low-contrast LM grating masks yielded similar spatial-frequency tuning functions around the modulation frequency of 1 cycle deg-1; (ii) low-contrast LM gratings masked the detection of test sinusoids in a highly phase-dependent fashion, while masking by CM gratings did not vary systematically with relative spatial phase. The results suggest that masking produced by CM gratings cannot simply be explained by the presence of a distortion product at the beat or modulation frequency.

High- and low-risk prostate cancer treated with 3D CT-guided brachytherapy: 1-to 5-year follow-up

PURPOSE

To provide a preliminary report of 301 patients treated for prostate carcinoma with three-dimensional CT-guided transischiorectal stereotactic brachytherapy using either iodine-125 or palladium-103 seeds as monotherapy.

PATIENTS AND METHODS

Patients with clinical stage T1, T(2ab), or T(3ab) disease with prostate volumes 23 to 180 cm3 and serum prostate specific antigen (PSA) concentrations of 0.9 to 143 ng/mL had seeds placed 10 mm apart under CT guidance. No androgen blockade was used postoperatively, but 47% of the patients had hormonal therapy preoperatively.

RESULTS

At 12 to 63 months (median 26 months) of follow-up, PSA concentrations had decreased to <2 ng/mL in 90% of the patients and to <1 ng/mL in 83%. Four patients underwent transurethral resection or incision at least 12 months after implantation; none became incontinent. Three patients had rectal ulceration that lasted for several months.

CONCLUSIONS

Computed tomography-guided transischiorectal brachytherapy allows accurate placement of radionuclide seeds in prostate glands of all sizes. The early results, as judged by serum PSA, are encouraging.

Response to replacement iron therapy in sideropenic individuals with recrudescent herpes labialis

This study investigated the effects of iron replacement on the incidence of recurrent herpes labialis and serum ferritin levels in patients with sideropenia. Ten patients with diagnosed sideropenia and a history of recrudescent herpes labialis were prescribed ferrous sulphate for a period of 3 months. Patients were questioned on the number of episodes of recrudescent herpes labialis that developed per month before treatment and the number of episodes of recrudescent herpes labialis that developed per month after the commencement of replacement iron therapy and during the follow-up period. All blood samples were collected by venipuncture for assay of ferritin levels. Serum ferritin levels were significantly increased compared to pretreatment levels (P<0.05). The number of monthly episodes of recrudescent herpes labialis was reduced from 0.78 to 0.2 episodes per month following treatment (P<0.05). The findings of this study suggest that iron replacement therapy should be further studied as a treatment option in sideropenic individuals with frequent recurrences of recrudescent herpes labialis.

Search for isovector giant monopole resonances via the Pb(3He,tp) reaction

The (nat)Pb(3He,tp) reaction at E(3He) = 177 MeV was studied to identify 2Planck's over 2piomega isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45<Q<-30 MeV in the coincidence data. The cross section is compared with distorted-wave Born approximation calculations for non-spin-flip and spin-flip isovector monopole resonances. The observed spin-flip and non-spin-flip monopole strengths in the proton-decay channel amount to 20% of the respective non-energy-weighted sum rule.

Purification and characterization of two mannan-binding lectins from mouse serum

Mannan-binding lectin (MBL) is a serum protein that activates the complement system after binding to glycoconjugates found on the surface of microorganisms. By molecular cloning two forms of MBL have been identified in the mouse (mMBL-A and mMBL-C), but only mMBL-A has been purified and characterized at the protein level. MBL-C has been termed the liver form of MBL. The present report describes the purification and characterization of mMBL-A and mMBL-C from serum. The two forms of mMBL could be separated both by ion-exchange and carbohydrate-affinity chromatography. The initial identification by immunochemical technique was confirmed by N-terminal amino-acid sequencing. Both proteins give bands corresponding to polypeptide chains of 28 kDa on SDS-PAGE in the reduced state, but mMBL-A migrated more rapidly than mMBL-C in acid/urea-PAGE, in accordance with the calculated pIs. Both forms mediated activation of complement component C4 in mannan-coated microtiter wells. MBL-A showed a higher affinity for d -glucose and alpha-methyl-d -glucose then did MBL-C. Serum concentrations of mMBL-A in laboratory strains and wild mice were found to vary from 5 to 80 microg/ml, with wild mice tending to show higher levels than laboratory strains.

Molecular characterization of P-29, a metacestode-specific component of Echinococcus granulosus which is immunologically related to, but distinct from, antigen 5

In this work the characterization of P-29, a novel 29 kDa antigen from Echinococcus granulosus is reported. E. granulosus was identified while looking for parasite antigens distinct from those present in hydatid cyst fluid. A monoclonal antibody (mAb 47H.PS) prepared against protoscolex components revealed that P-29 is localized to the tegument and rostellum of protoscoleces, and to the germinal layer of the cyst, but it is absent in hydatid cyst fluid or adult worm extracts. Several internal fragments of P-29 showed sequence identity to the amino acid sequence encoded by Eg6, a partial gene sequence reported to code for an epitope of antigen 5 (Ag5), one of the major diagnostic antigens of the parasite. We confirmed that Eg6 encodes a sub-fragment of P-29 by mapping the epitope of mAb 47H.PS, and isolating the full length P-29 cDNA. Since Eg6 had been, postulated to encode a fragment of Ag5, we specifically studied the relationship of P-29 and Ag5 by: (i) examining the cross-reactivity displayed by different mAbs; (ii) comparison of their peptide finger prints; and (iii) a comparative study of their diagnostic value. Our results prove unequivocally that P-29 and Ag5 are immunologically related, but different proteins, raising several questions on the current knowledge of Ag5.

Effects of glaucoma and aging on photopic and scotopic motion perception

PURPOSE

To examine the effects of primary open-angle glaucoma and normal aging on visual sensitivity for targets known to bias responses from the magnocellular visual processing stream.

METHODS

Contrast sensitivity was measured for the detection and direction discrimination of low-spatial-frequency (0.5 cyc/deg), drifting (4-24 Hz) sinusoidal gratings in 15 patients with glaucoma (mean age, 58.7 years), 14 age-matched control subjects (mean age 55.8 years), and 10 young control subjects (mean age, 24.4 years). As a control, sensitivity was measured for the detection of stationary stimuli. Stimuli of 4.7 degrees square were presented at either 0 degrees eccentricity or at 20 degrees along the nasal horizontal meridian, under both photopic and scotopic levels of lighting.

RESULTS

Across a wide range of conditions, the ability to detect and discriminate visual motion declined significantly (P < 0.05) with increasing age, whereas the ability to detect stationary patterns was generally unaffected. The rate of decline was adequately described by a simple linear function. Control studies showed that the age-related motion sensitivity losses could not be attributed solely to decreases in retinal illuminance associated with increasing age. Of note, however, there were no significant differences in mean sensitivity between glaucoma and age-matched control groups for any of the conditions used.

CONCLUSIONS

Even under conditions believed to bias the response of the visual system to the magnocellular pathway, glaucoma subjects could not be reliably differentiated from control subjects on the basis of mean sensitivity to motion stimuli. The findings have two broad implications: first, that substantial neural loss specific for motion perception occurs during the processes of normal aging, and second, that sensitivity to motion targets per se may not be a useful indicator of neural integrity in the early stages of glaucoma.

A single session, group study of exposure and Eye Movement Desensitization and Reprocessing in treating Posttraumatic Stress Disorder among Vietnam War veterans: preliminary data

This report summarizes data gathered thus far from an ongoing study. Two groups (total N = 12) of Vietnam War veterans diagnosed with Posttraumatic Stress Disorder (PTSD) received a single session of exposure or Eye Movement Desensitization and Reprocessing (EMDR) focusing on the veterans' most distressing war experience. Group assignment was random, treatment providers were blind to assessment data, and the pre- and posttreatment assessor was blind to treatment assignment. Both groups showed improvement on the Impact of Event Scale. EMDR treatment resulted in greater positive changes in within-session Subjective Units of Discomfort levels and on self-monitored severity of intrusive recollection. A trend toward decreased heart rate reactivity was observed in both groups. Results must be considered carefully due to the small number of subjects used in the study.

Separate colour-opponent mechanisms underlie the detection and discrimination of moving chromatic targets

Current opinion holds that human colour vision is mediated primarily via a colour-opponent pathway that carries information about both wavelength and luminance contrast (type I). However, some authors argue that chromatic sensitivity may be limited by a different geniculostriate pathway, which carries information about wavelength alone (type II). We provide psychophysical evidence that both pathways may contribute to the perception of moving, chromatic targets in humans, depending on the nature of the visual discrimination. In experiment 1, we show that adaptation to drifting, red-green stimuli causes reductions in contrast sensitivity for both the detection and direction discrimination of moving chromatic targets. Importantly, the effects of adaptation are not directionally specific. In experiment 2, we show that adaptation to luminance gratings results in reduced sensitivity for the direction discrimination, but not the detection of moving chromatic targets. We suggest that sensitivity for the direction discrimination of chromatic targets is limited by a colour-opponent pathway that also conveys luminance-contrast information, whereas the detection of such targets is limited by a pathway with access to colour information alone. The properties of these pathways are consistent with the known properties of type-I and type-II neurons of the primate parvocellular lateral geniculate nucleus and their cortical projections. These findings may explain the known differences between detection and direction discrimination thresholds for chromatic targets moving at low to moderate velocities.

Use of complete eluted peptide sequence data from HLA-DR and -DQ molecules to predict T cell epitopes, and the influence of the nonbinding terminal regions of ligands in epitope selection

In diseases with a strong association with an HLA haplotype, identification of relevant T cell epitopes may allow alteration of the pathologic process. In this report we use a reverse immunogenetic approach to predict possible HLA class II-restricted T cell epitopes by using complete pool sequencing data. Data from HLA-DR2(B1*1501), -DR3(B1*0301), -DQ2(A1*0501, B1*0201), and -DQ8(A1*0301, B1*0302) alleles were used by a computer program that searches a candidate protein to predict ligands with a relatively high probability of being processed and presented. This approach successfully identified both known T cell epitopes and eluted single peptides from the parent protein. Furthermore, the program identified ligands from proteins in which the binding motif of the HLA molecule was unable to do so. When the information from the nonbinding N- and C-terminal regions in the pool sequence was removed, the ability to predict several ligands was markedly reduced, particularly for the HLA-DQ alleles. This suggests a possible role for these regions in determining ligands for HLA class II molecules. Thus, the use of complete eluted peptide sequence data offers a powerful approach to the prediction of HLA-DQ and -DR peptide ligands and T cell epitopes.

Reproducing Kernel Hilbert space method for optimal interpolation of potential field data

The RKHS-based optimal image interpolation method, presented by Chen and de Figueiredo (1993), is applied to scattered potential field measurements. The RKHS which admits only interpolants consistent with Laplace's equation is defined and its kernel, derived. The algorithm is compared to bicubic spline interpolation, and is found to yield vastly superior results.

Use of eluted peptide sequence data to identify the binding characteristics of peptides to the insulin-dependent diabetes susceptibility allele HLA-DQ8 (DQ 3.2)

HLA-DQ8 (A1*0301, B1*0302) and -DQ2 (A1*0501, B1*0201) are both associated with diseases such as insulin-dependent diabetes mellitus and coeliac disease. We used the technique of pool sequencing to look at the requirements of peptides binding to HLA-DQ8, and combined these data with naturally sequenced ligands and in vitro binding assays to describe a novel motif for HLA-DQ8. The motif, which has the same basic format as many HLA-DR molecules, consists of four or five anchor regions, in the positions from the N-terminus of the binding core of n, n + 3, n + 5/6 and n + 8, i.e. P1, P4, P6/7 and P9. P1 and P9 require negative or polar residues, with mainly aliphatic residues at P4 and P6/7. The features of the HLA-DQ8 motif were then compared to a pool sequence of peptides eluted from HLA-DQ2. A consensus motif for the binding of a common peptide which may be involved in disease pathogenesis is described. Neither of the disease-associated alleles HLA-DQ2 and -DQ8 have Asp at position 57 of the beta-chain. This Asp, if present, may form a salt bridge with an Arg at position 79 of the alpha-chain and so alter the binding specificity of P9. HLA-DQ2 and -DQ8 both appear to prefer negatively charged amino acids at P9. In contrast, HLA-DQ7 (A1*0301, B1*0301), which is not associated with diabetes, has Asp at beta 57, allowing positively charged amino acids at P9. This analysis of the sequence features of DQ-binding peptides suggests molecular characteristics which may be useful to predict epitopes involved in disease pathogenesis.

Three types of postsynaptic glutamatergic receptors are activated in DMNX neurons upon stimulation of NTS

While it is widely accepted that parasympathetic activity plays a significant role in cardiovascular, bronchomotor, and gastrointestinal function, little is known about the synaptic control of parasympathetic vagal neurons. In this study, we identified the neurotransmitter(s) and postsynaptic responses in dorsal motor nucleus of the vagus (DMNX) neurons upon stimulation of the nucleus of the solitary tract (NTS). Neurons were visualized in rat brain stem slices, and perforated patch-clamp techniques were used to record postsynaptic currents. NTS stimulation activated glutamatergic currents in DMNX that were separated into N-methyl-D-aspartate (NMDA) and non-NMDA components using D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline-2,3-dione, respectively. The non-NMDA component was further characterized using cyclothiazide and concanavalin A to block desensitization of DL-alpha-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA) and kainate receptors, respectively. Cyclothiazide increased the postsynaptic amplitude, whereas concanavalin A augmented duration, suggesting kainate, but not AMPA, currents are curtailed by desensitization. High frequency stimulations did not alter synaptic efficacy. In conclusion, this study demonstrates the existence of a monosynaptic glutamatergic pathway from NTS that activates NMDA, kainate, and AMPA postsynaptic receptors in DMNX neurons.

Unique presentation of Crohn's disease during treatment of Hodgkin's disease

Although Hodgkin's disease and Crohn's disease are associated with abnormalities in cell-mediated immunity, their co-existence in an individual patient is uncommon. To our knowledge, this is the first report of the clinical presentation of Crohn's disease during treatment for Hodgkin's disease. The basic immunologic mechanisms underlying these two pathologic states as well as chemotherapy-related effects are postulated as potential etiologic mechanisms for the codevelopment of these diseases. A brief review of the literature and basic immunologic defects associated with Crohn's disease and Hodgkin's disease are presented.

Processing of major histocompatibility class I-restricted antigens in the endoplasmic reticulum

We have introduced long precursor peptides directly into the endoplasmic reticulum (ER) of a mutant cell line (T2-Db) that lacks the ability to transport peptides from the cytosol to the ER in a transporter associated with antigen processing (TAP) dependent way. This was done by expressing various influenza A-derived peptides containing the naturally processed epitope ASNENMDAM (366-374) preceded by the influenza hemagglutinin ER translocation sequence. Peptides derived from these minigenes that became associated with Db were isolated and identified by combined reversed phase liquid chromatography and detection by cytotoxic T lymphocytes. Our results establish that NH2-terminal extensions of at least 40 residues can be trimmed from peptides entering the ER, but that proteolysis of larger proteins may be limited.