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At least 91 records · Page 5Linked to original sources
PubMed2003

Metallic marker placement after stereotactic core biopsy of breast calcifications: comparison of two clips and deployment techniques.

OBJECTIVE: Two methods of deployment of metallic clips at the site of stereotactic core biopsy for breast calcifications are compared retrospectively. MATERIALS AND METHODS: One hundred nineteen clips deployed through an 11-gauge vacuum-assisted biopsy probe at core biopsy sites were compared with 109 vascular ligating clips deployed at biopsy sites using an 18-gauge spinal needle. The distance of each clip from the position of the target calcification was assessed using stereotactic coordinates in 52 sequential cases and was measured on mammograms before and after biopsy in 108 clips deployed through an 11-gauge probe and 98 clips deployed using an 18-gauge needle. Variance in clip position between postbiopsy and follow-up mammograms was measured in 43 clips placed with an 11-gauge probe and in 44 clips placed with an 18-gauge needle. Comparable measurements of variance in position of fat necrosis calcifications between screening mammograms were used as controls. RESULTS: Ninety-seven percent of the clips placed with an 11-gauge probe and 98% of the clips placed using an 18-gauge needle were within 1 cm of the target calcifications using stereotactic coordinates. On mammograms obtained after biopsy, 70% of the clips placed with an 11-gauge probe and 63% of the clips placed using an 18-gauge needle were within 1 cm of the target calcifications, and the position of 91% of the clips placed with an 11-gauge probe and 90% of the clips placed using an 18-gauge needle varied less than 15 mm on follow-up mammograms. Both clips provided accurate targets for wire-localized excisions. The cost of the 11-gauge needle and clip is $320. The 14-gauge probe, vascular clip, and 18-gauge spinal needle cost $191.58. CONCLUSION: A vascular ligating clip delivered to a stereotactic core biopsy site by an 18-gauge spinal needle is comparable in apparent accuracy and stability to a clip deployed through an 11-gauge probe. This technique allows core biopsies to be performed with instruments smaller than 11-gauge and at a 40% savings in equipment cost.

Biopsy, Needle↗
PubMed1985

A clinical evaluation of absorbable polydioxanone ligating clips in abdominal and pelvic operations.

An absorbable vascular ligating clip made of polydioxanone polymer was evaluated in 44 patients who underwent abdominal and pelvic operations. These clips were used in place of conventional metallic clips primarily in performing pelvic and para-aortic lymphadenectomy. The polydioxanone clips were found to be superior to the metallic clips in ease of clip loading to the applier, security of clips in the transfer to the surgeon and security of the clip in the applier when positioning to ligate vessels. The use of polydioxanone clips, which absorb within 210 days, may also lead to improved CAT or NMR imaging by precluding energy scatter which is known to occur with some metallic clips. Clip applier function, security on tissues ligated and clip visibility were equivalent to previous experience using metallic clips. Selection of proper clip size is important so that excessive amounts of tissue are not contained within the clip jaws which might prevent clip closure. No postoperative complications were noted in the use of these clips.

Absorption↗
PubMed1994

Comparison of titanium and absorbable polymeric surgical clips for use in laparoscopic cholecystectomy.

The use of hemostatic surgical clips is crucial in laparoscopic surgery. Metal clips can cause significant interference with computerized tomography, may have poor holding power, and may erode into important anatomic structures. Polymeric absorbable clips, which have advantages over metallic clips, are evaluated in this study. In vitro and in vivo studies were undertaken to evaluate the hold force, rate of degradation, tissue reactivity and safety of absorbable polymeric clips. Absorbable and titanium clips were applied across excised canine cystic ducts and both axial and transverse pull-off forces were measured. In the second phase, absorbable clips were implanted subcutaneously into male rats and the strength remaining within the clips was measured after 7, 10, 14, or 21 days. In phase 3, 30 pigs were randomized into six groups and each animal underwent a laparoscopic cholecystectomy. The cystic duct and artery were ligated with absorbable polymeric clips (experimental group) or titanium clips (control group). Animals were sacrificed at 7, 14, or 28 days and a celiotomy was performed. Intraabdominal adhesions were assessed and scored. The force required to dislodge the absorbable clip was significantly greater than for metallic clips for both axial and transverse forces. Absorbable clip strength retention decreased over time as expected with a retention of 11% original strength by the 21st day. Adhesions were highest when bile spillage occurred, but did not differ significantly between either clip type. Absorbable polymeric clips were hemostatically effective in this laparoscopic model and may offer advantages over metallic clips.

Animals↗
PubMed1997

A comparative study of intracranial aneurysm clips: closing and opening forces and physical endurance.

OBJECTIVE: The closing and opening forces of various types of intracranial aneurysm clips were measured, and the physical endurance of the clips was evaluated. METHODS: Straight, bayonet, angled, fenestrated, and temporary Sugita and Yasargil clips were tested by measuring the forces exerted by the blades as they were opened in wider increments and at various points along their length by a specially designed clip tester. Closing forces after repeated openings, continuous opening, or multiple sterilization procedures also were measured. RESULTS: The opening forces of Yasargil clips increased linearly and more sharply as the blades were opened wider than those of Sugita clips. Only Sugita clips showed significant differences between the opening and closing forces (hysteresis). Closing forces of all of the tested clips were according to a hyperbolic curve. Straight clips showed a sharper rise in closing forces than those of bayonet, angled, or fenestrated clips. A relatively weak closing force at the tip of Yasargil long clips and a strong closing force at the base of temporary clips were unexpected findings. The closing force decreased by only 3 to 7% after 500 openings and did not decrease after continuous opening for 17 hours or 100 sterilization procedures. CONCLUSION: Our study showed that the closing forces differed depending not only on the distance of the point of measurement from the clip spring but also on the shapes of the clip blades. Repeated opening or sterilization of the clips did not significantly decrease the closing forces of the aneurysm clips.

Biomechanical Phenomena↗
PubMed1982

Histological change in permanently clipped or ligated cerebral arterial wall. Part I. An experimental study in dogs.

In this paper, we discuss the results of a study by light microscope of the effect of permanent clipping or ligation on the intracranial arteries of 38 operation dogs and 7 control dogs. The findings obtained are: 1. In the cerebral arterial circle, necrosis could easily result from ordinary clipping or ligation because of scarce vasa vasorum. 2. As for the incidence of necrosis, the greatest was found in the case of the Yaşargil clip after electric coagulation, next came the Yaşargil clip alone, next ligation, and last the silver clip. The degree of necrosis correlated with the duration of clipping in the cases treated with a spring type clip, and was influenced more by the closing strength at the time of application in the cases with non-spring type clips or ligation. 3. In some of the cases ligated for long duration, recanalization was caused by the passage of the ligature through the vessel wall, suggesting that ligation is not a certain procedure if it is applied alone. 4. The granulation tissue round the clip and ligature began to grow after one month. As for its degree, the most marked granulation was that caused by the silver clip, next the ligature, than the Yaşargil clip after electric coagulation, and finally the Yaşargil clip used normally; in all of them the correlation with the passage of time was noted. 5. In the group of duration three months or more, concentric intimal proliferation was noted peripheral to the clip, and intimal proliferation was also noted exclusively localized to the side of a branch on the central or truncal side of a clip. This correlated in degree with the passage of time. 6. Clipping and ligation are liable to cause necrosis and fragmentation, but on the other hand it was considered that rupture of the vessel wall did not result because of the reinforcing and reparative effect of the reactive granulation tissue and the intimal proliferation which developed in such a manner as to strengthen the area involved.

Animals↗
PubMed1998

Clinical analysis of internal carotid artery aneurysms with reference to classification and clipping techniques.

An intraoperative classification of intradural internal carotid artery (ICA) aneurysms not related to the arterial division but based on their operative presentation and clipping techniques is introduced. On the basis of the surgeon's view of the operative field via the pterional approach in 156 operated intradural ICA aneurysms in 143 patients, these aneurysms were classified according to their location in relation to the long axis of the ICA as either proximal, middle or distal in type and also according to their relation to the cross section of the ICA as either lateral, medial, ventral or dorsal in type. Numerically the largest in frequency is the middle type of aneurysm by axial location and the lateral type of aneurysms by cross sectional location. Eighty five percent of the lateral type aneurysms were at the arterial division. The majority of the large to giant aneurysms were of the ventral type and no dorsal type aneurysms were seen. About one third of the ICA aneurysms in this series were located free of the arterial division. All dorsal type aneurysms and most of the medial type aneurysms were not related to the arterial division. Clipping techniques were classified into perpendicular and parallel clipping, as to the direction of the clip-blades in relation to the carotid axis. The parallel clipping was further classified into forward clipping, in which a clip was applied from the distal side of the ICA, and reversed clipping, in which a clip was applied from the proximal side of the ICA. Most of the aneurysms located at the arterial division required the perpendicular clipping and those free of the arterial division required the parallel clipping. Furthermore, the forward clipping was useful for proximal type aneurysms and the reversed clipping for distal type aneurysms. For the middle type aneurysms clipping was performed bidirectionally. This classification includes all types of the ICA aneurysms located at any points along its long axis and on its cross section, and is useful for planning safe and exact clipping of the ICA aneurysms.

Adult↗
PubMed1998

Identification and expression of two novel CLIP-170/Restin isoforms expressed predominantly in muscle.

CLIP-170 and Restin, microtubule-binding proteins originally cloned from human cells, are identical except for a stretch of 35 amino acids present in Restin, but missing from CLIP-170. Here we present the discovery of two novel isoforms of the CLIP-170/Restin gene in both chickens and humans. One of the new isoforms, named CLIP-170(11), contains an 11 amino acid insert instead of the 35 amino acid insert found in Restin. Eight of these 11 amino acids, including a helix-breaking proline residue, are perfectly conserved between chickens and humans. The second new isoform, named CLIP-170(11+35), contains both the 11 and 35 amino acid inserts in tandem. PCR analysis of chicken genomic DNA revealed that all four isoforms result from differential splicing of two exons in a region of the CLIP-170 gene that contains approximately 8.6 kb of intervening sequence. We found that the CLIP-170(11) and CLIP-170(11+35) are expressed preferentially in muscle tissues. Chicken and human skeletal muscle express predominantly CLIP-170(11) and to a lesser extent CLIP-170 and CLIP-170(11+35). Adult chicken cardiac and smooth muscles also express CLIP-170(11) and CLIP-170(11+35), but CLIP-170 is the predominant isoform in these muscles as it is in all other tissues except brain. The ratios of CLIP-170 isoform expression found in embryonic and adult chicken cardiac muscles reveal that isoform expression is regulated differentially in different developmental stages as well as in different tissues.

Alternative Splicing↗
PubMed1996

Titanium aneurysm clips: Part I--Mechanical, radiological, and biocompatibility testing.

Most aneurysm clips are made of cobalt-based alloys. Although these clips are nonferromagnetic, they still produce artifact that degrades the quality of magnetic resonance (MR) images. A new aneurysm clip of pure titanium was developed to minimize artifact on postoperative MR images. We evaluated these clips in a series of mechanical tests in vitro, biocompatibility tests in rabbits, and radiological tests in greyhound dogs. The clip sizes and shapes matched those of conventional aneurysm clips. The average closing forces ranged between 151.6 and 181.8 g and were not diminished by repeated sterilization or stress. After > 20 million cycles of high-pressure and high-frequency pulsations, the clips did not open and the closing forces were not reduced. Titanium aneurysm clips implanted in the subarachnoid space of 12 rabbits for 1 or 6 months produced mild gliosis identical to that produced by implantation of cobalt alloy clips in 12 control rabbits. Based on pre- and postoperative weights and electron microscopic scans, the titanium implants did not corrode. The artifact on computed tomographic and MR imaging produced by a titanium clip placed on the internal carotid artery of a greyhound was less than that produced by an identical cobalt-chrome alloy clip by a factor of two to three. This study demonstrated that titanium aneurysm clips are mechanically equivalent to conventional clips, biocompatible, and corrosion resistant. Furthermore, titanium clips have superior imaging characteristics, creating less computed tomographic and MR imaging artifact and permitting better resolution of anatomic structures than cobalt alloy clips.

Animals↗
PubMed2004

[Growth and resource allocation pattern of Artemisia frigida under different grazing and clipping intensities].

In order to understand the degradation process and its mechanism of typical steppe in Inner Mongolia, this paper studied the growth and resource allocation pattern of Artimisia frigida under different grazing and clipping intensities(no grazing, light grazing 1.33 sheep.hm-2, moderate grazing 4.00 sheep.hm-2, heavy grazing 6.67 sheep.hm-2, proportional clipping and stubble clipping), which was conducted at the Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences(43 degrees 26'-44 degrees 08' N, 116 degrees 04'-117 degrees 05' E). The results showed that the regrowth ability of A. frigida under proportional clipping was superior to that under stubble clipping, and light clipping (1/4 proportional clipping or 10 cm stubble clipping) was superior to no clipping. In early growth season, the net regrowth of A. frigida was higher under no clipping than under light clipping, but reversed in late growth season (after mid-August). The biomass allocation pattern of A. frigida was roots > leaves > stems. Grazing or clipping affected biomass allocation significantly, especially for the allocation of leaves and flowers. The biomass allocation of leaves was significantly higher under 3/4 proportional clipping or 4 cm stubble clipping than under other treatments, and reverse trend was true for the biomass allocation of flowers. There were no significant differences in biomass allocation of roots and stems among treatments. Sexual reproductive allocation decreased with increasing grazing or clipping intensities, and reproductive mode of A. frigida changed under heavy grazing. The changes in priority of biomass allocation from sexual reproductive organs to clonal growth to sustain and propagate population were important ecological strategies of the species to heavy grazing.

Animal Husbandry↗
PubMed2003

A comparison of holding strength of various surgical clips.

Due to advances in clip design, new types of surgical ligation clips are available that may reduce clip failure and improve function, especially for 5-mm clip appliers. We tested a preformed spring clip based on a 5-mm applier against other commonly used clips from 5- and 10-mm multiloading clip appliers. Five different clips were compared using a digital force gauge to test perpendicular pulloff force after application to tubing of varying thickness and compliance. The average pull-off force for commonly used 5-mm and 10-mm clip appliers was 0.29 +/- 0.06 and 0.35 +/- 0.05 kg, respectively. Average pull-off force for the new preformed spring clip was 0.53 +/- 0.07 kg (p <0.0001). The new clip technology has significantly higher pull-off force than other currently used clips. This may be particularly beneficial in procedures requiring 5-mm clip appliers, which are known to place clips with lower holding force.

Equipment Failure↗
PubMed2006

Comparison of holding power of metal and absorbable hemostatic clips.

PURPOSE: Metal hemoclips remain in the tissue permanently. Metal clips will interfere with the interpretation of a computed tomography or magnetic resonance imaging scan. Polydixanone polymer clips (Absolak extra clips; Ethicon Endo-Surgery, Cincinnati, OH) are completely absorbable. Absolak extra clips will not interfere with a computed tomography or magnetic resonance imaging scan and will encircle 360 degrees vessels for extra security. The aim of this study was to test the holding strength of the metal hemoclips and Absolak clips and the amount of pressure that will cause slippage of the 2 types of clips. METHODS: The study period was from April 2001 to December 2002 and the study included 74 patients undergoing colectomy. There were 40 men and 34 women. Patient ages ranged from 33 to 86 years (average, 64.5 y). The clips were applied on the dissected vessels of the specimen. Part I of the study was as follows: a rubber band was applied to the protruding part of the clip and a balance weight then was tied onto the rubber band. The weight was increased gradually by 50-g units. The weight that caused slippage of the clip was recorded. Part II of the study was as follows: a correctly sized angiocatheter was inserted individually into the artery and vein and attached to a sphygmomanometer. The intravascular pressure was increased by inflating the balloon of sphygmomanometer and the amount of pressure that caused slippage of the clips was recorded. RESULTS: Part I of the study determined that an artery could hold 406.4 +/- 46.1 g, a vein could hold 247.3 +/- 36.5 g, and both arteries and veins could hold 621.6 +/- 24.9 g without slippage when a single hemoclip was applied. No slippage occurred when an Absolak or double hemoclips were applied to the vessel(s). Part II of the study determined that a hemoclip would slip off of a vein when the pressure was increased to 156.6 +/- 8.4 mm Hg. Double clips would slip off of a vein when the pressure was increased to 257.6 +/- 9.6 mm Hg. No hemoclip slipped off of an artery after application even if the amount of pressure was increased to 300 mm Hg. No Absolak clip slipped off after application to an artery or vein even if the amount of pressure was increased to 300 mm Hg. CONCLUSIONS: Absolak clips can withstand a higher weight than single hemoclips without slipping off of an artery and/or vein. Likewise, Absolak clips can withstand a higher intravascular pressure without slippage than single or double hemoclips when applied to a vein.

Adult↗
PubMed1999

New aneurysm clip and applier for narrow spaces: technical note.

OBJECTIVE: Aneurysm surgery carries considerable risk to the patient, in part because the surgical field can be so constricted that accurate placement of the aneurysm clip is impeded. In fact, most aneurysm clip appliers are so bulky that they can impair the surgeon's view, if the field is tight. We describe a system of aneurysm clips and appliers that have a very low profile and consequently allow better visualization of the operative field at critical moments during surgery. INSTRUMENTATION: A new system of clips for aneurysm surgery was developed to overcome some of the deficiencies of conventional sets. The new clip blades are opened from inside the spring, so the clip blades are clearly seen as they are applied across the base of the aneurysm. In addition, these clips can be angled in any desired direction in the applier, which makes their application easier. A third advantage is that the clip applier is used as a clip remover should adjustment or reapplication of the clip be necessary. RESULTS: Thirty aneurysms were obliterated with the new clips without any complications attributable to the clips. The new instruments allowed the safe application of clips to aneurysms in deep, confined, and anatomically complex spaces, such as aneurysms of the basilar tip and anterior communicating artery. CONCLUSION: The newly described system of aneurysm clips and appliers appears to have significant advantages over other currently available systems.

Animals↗
PubMed2005

The microtubule plus-end-tracking protein CLIP-170 associates with the spermatid manchette and is essential for spermatogenesis.

CLIP-170 is a microtubule "plus-end-tracking protein" implicated in the control of microtubule dynamics, dynactin localization, and the linking of endosomes to microtubules. To investigate the function of mouse CLIP-170, we generated CLIP-170 knockout and GFP-CLIP-170 knock-in alleles. Residual CLIP-170 is detected in lungs and embryos of homozygous CLIP-170 knockout mice, but not in other tissues and cell types, indicating that we have generated a hypomorphic mutant. Homozygous CLIP-170 knockout mice are viable and appear normal. However, male knockout mice are subfertile and produce sperm with abnormal heads. Using the knock-in mice, we followed GFP-CLIP-170 expression and behavior in dissected, live testis tubules. We detect plus-end-tracking GFP-CLIP-170 in spermatogonia. As spermatogenesis proceeds, GFP-CLIP-170 expression increases and the fusion protein strongly marks syncytia of differentiated spermatogonia and early prophase spermatocytes. Subsequently GFP-CLIP-170 levels drop, but during spermiogenesis (post-meiotic development), GFP-CLIP-170 accumulates again and is present on spermatid manchettes and centrosomes. Bleaching studies show that, as spermatogenesis progresses, GFP-CLIP-170 converts from a mobile plus-end-tracking protein to a relatively immobile protein. We propose that CLIP-170 has a structural function in the male germline, in particular in spermatid differentiation and sperm head shaping.

Animals↗
PubMed1998

Titanium aneurysm clips: mechanical characteristics and clinical trial.

Titanium clip is well documented to reduce the artifact observed in computed tomography (CT) or magnetic resonance (MR) imaging and improve the quality of these images. There are, however, some demerits based on metallic characteristics including large spring portions, lack of long and fenestration clips, and difficulties to produce. We examined the mechanical characteristics of Sugita titanium aneurysm clips (product of 6 aluminium-4 vanadium-titanium) and investigate the safety in clinical use and the imaging quality compared with those of cobalt (Co) alloy clips. On mechanical test, Sugita titanium clips showed no significant difference in closing force compared with the conventional Co alloy clips. The closing force reduced about 10% after 100 times repeated opening in titanium clips in contrast with no remarkable changes in Co alloy clips. Sixty-four patients with ruptured or unruptured cerebral aneurysms (total number of 71 aneurysms) were treated with Sugita titanium clips through the microsurgical technique. None of the unfavorable outcome occurred in related to the titanium clips. Neither clip dislocation nor deformation was experienced in this series during the follow-up period. The clip artifacts seen in CT and MR image were markedly reduced, however, MR angiography had less quality to resolve anatomical structures due to an existence of vessel gap. These results indicate that in spite of some disadvantages, Sugita titanium clips allow safe and beneficial use routinely in aneurysm surgery insofar as the complete clipping is obtained.

Biomechanical Phenomena↗
PubMed2006

Reliability of cobalt-chromium alloy aneurysm clips after long-term implantations in patients with cerebral aneurysms.

OBJECT: Aneurysm clip reliability after long-term implantation in vivo has not been examined. In this study the authors evaluated the mechanical properties and surface elemental composition of Co-Cr alloy aneurysm clips implanted for more than 10 years in patients with cerebral aneurysms. METHODS: Five aneurysm clips implanted for ruptured or unruptured intracranial aneurysms were retrieved and examined. New aneurysm clips were applied to the regrown aneurysms. The implantation period ranged from 11 to 20 years. Four new and unused aneurysm clips were also examined as controls. The mechanical properties of the clips were tested by measuring their closing force and bending strength. The surface elemental composition of the aneurysm clips was evaluated using x-ray photoelectron spectroscopy. The closing force of the retrieved clips exceeded the minimum force requirement at the time of manufacture. The bending strength was similar between the retrieved and control clips. Chromium oxide was the predominant constituent on the surface of all clips, and its concentration on the retrieved clips was higher than that on the control clips. CONCLUSIONS: Data in the present study demonstrated that Co-Cr alloy aneurysm clips retain their mechanical properties in vivo for a long time, which indicates the reliability of these clips.

Aged↗
PubMed1988

A comparative scanning electron microscopic study on degradation of absorbable ligating clips in vivo and in vitro.

Using scanning electron microscopy, the degradation characteristics of two absorbable ligating clips, Absolok (polydioxanone) and Lactomer (poly-L-lactide-co-30%-glycolide) have been studied under in vivo and in vitro conditions. The rate of Absolok clip degradation was significantly greater than that of Lactomer clip degradation both in vitro and in vivo. The rate of degradation of Lactomer clips significantly increased and they showed a greater change in proportion of breakdown in vivo than in vitro compared to Absolok clips. The Absolok clip breakdown began with the formation of surface undulations which later developed into fissures. The undulations appeared on the clip surface as early as 7 days and by 2 weeks developed into fissures. The initial appearance of the fissures was at the edge of the clips particularly at the mating surface. The thickness of layers forming the fissures gradually decreased and by 15 weeks the layers appeared as very thin sheets of materials. The high energy areas (locking and molding points) were more resistant to breakdown and the remains of the clips were still present 25 weeks after initiation of the experiments. The Lactomer clips showed very little sign of degradation in vitro even after 10 weeks of incubation. However, in the in vivo experiments undulations formed on the clip surface as early as 2 weeks postimplantation. These clips also showed fissures similar to those observed on Absolok clips.

Animals↗
PubMed1999

Virtues and drawbacks of titanium alloy aneurysm clips.

This report describes the imaging characteristics of titanium alloy aneurysm clips and our clinical experience with these clips in more than 300 patients. Phantom and clinical investigations showed that clip artifacts on CT and MR are minor as compared to the cobalt alloy clips used previously. Spiral CT angiography (CTA) in combination with titanium alloy clips could be shown to be a feasible mode of postoperative control and can be used to determine completeness of aneurysm elimination, patency of adjacent arteries as well as vasospasm. In contrast, magnetic resonance angiography (MRA) proved to be unfeasible as a method of postoperative vascular imaging since the titanium clips still produce a shadow in the order of size of the entire aneurysm. Therefore, completeness of aneurysm elimination cannot be judged on magnetic resonance angiography. The clinical experience in more than 300 cases showed that the titanium alloy clips essentially performed well. However, the limits of elastic deformation appear to be somewhat inferior to cobalt alloy clips. The standard appliers do not open the blades of the titanium clips quite as far as with the comparable cobalt alloy clips and the corresponding appliers. Therefore the titanium aneurysm clips are not quite as well suited for large broad based aneurysms. Furthermore, the increased susceptibility of the new clips with regard to abuse suggests to follow the recommendations of the manufacturer not to recycle and re-sterilize clips that have been tried but not permanently implanted.

Alloys↗
PubMed1995

Clip binds to HLA class II using methionine-based, allele-dependent motifs as well as allele-independent supermotifs.

The invariant chain (Ii) region that interacts with class II and inhibits premature peptide binding has been mapped to amino acids 82-107, known as CLIP. It is unclear whether CLIP binds directly to the class II peptide binding groove and thus competitively blocks binding of other peptides, or whether it binds to conserved class II sites and indirectly inhibits peptide binding by inducing conformational changes in class II. Here we show evidence that strongly suggests that CLIP binds within the peptide binding groove, as CLIP binds to various HLA-DR alleles using allele-dependent as well as allele-independent, methionine-based binding motifs. First, a core sequence of 12 amino acids was identified within CLIP which is required for optimal binding to DR1, DR2, DR3(17) and DR7. This sequence is composed of CLIP p88-99 (SKMRMATPLLMQ). By substitution analysis, all three methionine residues appeared to control CLIP binding to HLA-DR. However, whereas M90 controlled binding to all four alleles, M92 and M98 were of different importance for the various alleles: M92 is involved in CLIP binding to DR1 and DR3(17) but not to DR2 or DR7, and M98 controls CLIP binding to DR2, DR3(17) and DR7 but not DR1. Also, CLIP competes with known immunogenic peptides for class II binding in a manner indistinguishable from regular, class II binding competitor peptides. Finally, the dissociation rates of CLIP-class II complexed are similar to those of antigenic peptide-class II complexes. Thus, CLIP most likely binds to the class II peptide binding groove, since most allelic class II differences are clustered here. CLIP uses unconventional methionine anchor residues representing an allele-independent supermotif (M90) as well as allele-dependent motifs (M92 and M98).

Alleles↗