Quinolones as gonadotropin releasing hormone (GnRH) antagonists: simultaneous optimization of the C(3)-aryl and C(6)-substituents

A series of 3-arylquinolones was prepared and evaluated for their ability to act as gonadotropin releasing hormone (GnRH) antagonists. A variety of substitution patterns of the 3-aryl substituent are described. The 3,4,5-trimethylphenyl substituent (23h) was found to be optimal.

Potent antagonists of gonadotropin releasing hormone receptors derived from quinolone-6-carboxamides

SAR studies which focused upon the C-6 position of a recently described series of quinolone gonadotropin releasing hormone antagonists are reported. Synthetic access to diverse quinolone-6-carboxamides was achieved via the palladium-catalyzed amino-carbonylation reactions of iodide 4 with various amines. Amides related to 9y were especially potent, functional antagonists of rat and human GnRH receptors.

Coccolith ultrastructure and biomineralisation

The relationship between calcite biomineralisation and coccolith ultrastructure is analysed across the diversity of calcifying haptophytes. The emphasis is on integration of evidence from crystallographic and ultrastructural studies but additional relevant information from biochemical and phylogenetic work is reviewed. We attempt to identify aspects of ultrastructure which are most likely to be the product of self-organising processes. The principal topics reviewed are heterococcolith rim nucleation, including reassessment of the V/R model; crystal growth regulation in heterococcoliths; holococcolith biomineralisation; and the diversity of other biomineralisation modes in haptophytes. It is concluded that the diverse range of calcareous structures produced by haptophytes probably has a common phylogenetic origin and is produced via operation of a limited set of mainly shared genetic and biochemical pathways. Copyright 1999 Academic Press.

Cloning and modeling of the first nonmammalian CD4

We have cloned and sequenced the first nonmammalian CD4 cDNA from the chicken using the COS cell expression method. Chicken CD4 contains four extracellular Ig domains that, in analogy to mammalian CD4, are in the order V, C2, V, and C2. The molecule is 24% identical with both human and mouse sequences. The extracellular domains were modeled using human and rat CD4 crystal structures as templates. In the first domain there are two extra Cys residues that are at suitable distance to form an intra-beta-sheet disulfide bridge in addition to the canonical one in the V domain. The region responsible for the interaction with MHC class II is relatively nonconserved in chicken. However, there are positively charged amino acids in the C" region of the N-terminal domain that may mediate the association to the negatively charged residues of the MHC class II beta-chain. Molecular modeling also implies that the membrane-proximal domain mediates dimerization of chicken CD4 in a similar way as it does for human CD4. Furthermore, the cytoplasmic tail is highly conserved, containing the protein tyrosine kinase p56lck recognition site that is preceded by an adjacent di-leucine motif for the internalization of the molecule. Interestingly, there are no Ser residues in the cytoplasmic part, which may explain the slow down-regulation of chicken CD4 after phorbol ester stimulation.

The natural history of asymptomatic moderate internal carotid artery stenosis by duplex ultrasound

The purpose of this study was to determine the rate of progression of the degree of carotid stenosis and to determine the risk of continued observation in a group of asymptomatic patients with moderate stenosis of at least one internal carotid artery. Between 1989 and 1994, 2130 patients were found to have 60-79% stenosis of at least one internal carotid artery following a duplex ultrasound examination in the authors' vascular laboratory. Of these, 465 patients (255 men, 210 women) were asymptomatic and had more than one ultrasound examination, and they form the basis of this retrospective review. The mean +/- SD age was 68.8 +/- 9.0 years. The mean +/- SD number of ultrasound examinations was 3.1 +/- 1.4 (range 2-11). The mean +/- SD follow-up was 24.4 +/- 17.6 months (range 2-79 months). Over the period of follow-up 72 patients (15.5%) progressed to 80-99% stenosis (n = 71) or to occlusion (n = 1). The estimated percentage of patients who progressed by life table methods were 5 +/- 1% at 1 year, 11 +/- 2% at 2 years and 20 +/- 3% at 3 years. There was no statistically significant difference in the rate of progression in men compared with women. Twenty-one patients had a late ipsilateral TIA or stroke. Five out of 72 patients (6.9%) who progressed had a late ipsilateral TIA compared with nine out of 393 patients (2.3%) who did not progress (estimated risk ratio 16.1, P = 0.0001). Four out of 72 patients (5.6%) who progressed had a late ipsilateral stroke compared with three out of 393 patients (0.76%) who did not progress (estimated risk ratio 23.6, p = 0.0002). The cumulative ipsilateral stroke rate using life table methods was 0.22% at 1 year, 1% at 2 years and 2.4% at 3 years. In a large cohort of asymptomatic patients, the frequency of progression of 60-79% internal carotid artery stenosis was 5% at 1 year, 11% at 2 years and 20% at 3 years. Patients who progressed were more likely to have symptoms, but the rate of unheralded stroke was relatively low over a 3-year time period. Surveillance carotid ultrasound examinations should be performed in patients with moderate carotid stenosis. Because of the lack of clear benefit, carotid endarterectomy for asymptomatic 60-79% internal carotid artery stenosis cannot be justified.

Cytokeratin expression in breast cancer: phenotypic changes associated with disease progression

Transition from a normal to a cancerous state is marked by alterations in the cytoskeletal structure of those cells involved. We have examined such changes to determine if these transitions are markers of disease progression. Cytokeratin (CK) protein and messenger RNA (mRNA) expression were examined in malignant and benign breast tissues. Flow cytometric results demonstrated a significant correlation between cytokeratin protein expression detected by 5D3 antibody, specific for cytokeratins 8, 18, and 19 and axillary node metastasis (P = 0.01). A threshold of positivity of 338,000 molecules/cell was determined and reflected the wide range in cytokeratin levels expressed by normal or benign tissues. Examination of cytokeratins 8, 18, and 19 revealed a consistent pattern of expression with respect to tumor grade. Only cytokeratin 19 showed significant correlation with increasing tumor size (P = 0.006). mRNA expression for cytokeratin 8 was significantly higher in node-positive compared with node-negative disease (P = 0.02). Cytokeratin 18 mRNA levels were significantly lower in both node-negative (P = 0.03) and node-positive (P = 0.02) patients when compared with benign samples. Increased levels of cytokeratin 18 mRNA showed an inverse relationship with protein expression (P = 0.05). The results indicate that cytokeratin expression in breast cancer may be associated with tumor progression. Furthermore, the alteration in the expression of individual cytokeratins deserves further investigation to determine the consequences of these changes with respect to cellular function.

The structure of avian CD5 implies a conserved function

The chicken CD5 cDNA was isolated by COS cell expression cloning utilizing a novel mAb 2-191. The cDNA contains a 1422-nucleotide open reading frame encoding a mature protein with 32% and 30% identity to mouse and human CD5 polypeptides, respectively. The molecule consists of a 330-amino acid extracellular region with three repeats of the scavenger receptor cysteine-rich domain, a 29-amino acid hydrophobic transmembrane domain, and a 93-amino acid cytoplasmic tail. The cytoplasmic region contains motifs that are highly conserved between species, including several potential phosphorylation sites. The chicken CD5 is a 64-kDa phosphorylated glycoprotein with a protein core of 57 kDa as determined by immunoprecipitation and SDS-PAGE analysis. Alphabeta T cells express a homogeneously high level of CD5, whereas low or intermediate CD5 expression on gammadelta T cells depends on their tissue location. In contrast to human and mouse, CD5 is found at low levels on all chicken B cells. The high conservation of structural features, as well as signaling motifs, implies a conserved role for CD5 both in lymphocyte development and function.

Individual variation in male vocal traits and female mating preferences in Bufo americanus

We investigated the amount of variation in mating behaviour between and within individual male and female American toads, because both sources of trait variation can influence the course of sexual selection. Males varied in all four call parameters investigated (dominant call frequency, pulse rate, call rate and call duration). Individual males lowered the dominant frequency of their call when they interacted vocally with nearby males. Dominant call frequency was more highly correlated with body size in vocally interacting males than in non-interacting males. Pulse rate of calls primarily varied with water temperature. Call rate and call duration showed the most variation of the four call properties, but this variation was unrelated to male morphology or social interactions. Females varied in three aspects of mating behaviour: two measures of pair formation and their preference for dominant frequency of male calls. The body size of paired males varied between females both in pairings initiated by either sex and in pairings initiated only by females. Males chosen by females were usually larger than average, although age and prior breeding experience of females did not affect mate choice. Playback experiments indicated that female preference for calls of low dominant frequency depended on the temporal patterning of alternative calls presented. Each of the four male vocal properties showed significant repeatability, but only one of the three aspects of female mating behaviour was repeatable. We discuss how different degrees of repeatability in sexual traits of males and females may influence the action and detection of sexual selection in this and other species. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

The effect of 3-week tamoxifen treatment on oestrogen receptor levels in primary breast tumours: a flow cytometric study

The effect of 3-week, preoperative tamoxifen treatment on oestrogen receptor (ER) levels, expressed by primary breast tumours, was examined. Patients (age-matched) with breast cancer, confirmed by fine-needle aspiration, were either treated with 20 mg ml(-1) oral tamoxifen per day or received no medication in the 3-week interval between assessment and surgery. Quantification of ER using flow cytometry was performed on the surgically removed tumour samples from tamoxifen-treated (n = 40) and control (n = 38, untreated) patient groups. The tumours were mechanically disaggregated, and saponin treatment rendered these cells permeable to antibodies. Using dual-parameter labelling with a FITC-conjugated antibody (NCL-5D3) directed against cytokeratin 8/18/19 and a biotinylated antibody (DAKO-ER 1D5) directed against the oestrogen receptor, ER quantification was determined on a number of receptors per cell basis. Using QC quantum bead standards, ER levels in the epithelial cell population, the non-epithelial cell population and the whole-cell population (ER+) were calculated. ER levels were significantly lower in the total cell population than tamoxifen-treated patients (P = 0.002) when compared with the control (untreated) group. By using a gating procedure using 5D3 antibody positivity, a significantly lower level was detected on examining the cytokeratin-positive population alone (P = 0.006). Using a complementary gating technique, ER levels were quantified in the cytokeratin-negative cell population. Examination of this group of cells showed no significant difference between the levels of oestrogen receptor found in the tamoxifen-treated and untreated groups (P = 0.4). We have demonstrated that ER levels can be monitored by flow cytometry. ER levels in patients treated with tamoxifen 3 weeks before operation are significantly lower than in a comparative group of patients who received no drug. Furthermore, the most significant difference in receptor levels is seen by quantification of total ER levels expressed by all the tissue.

Heparin administration via nomogram versus a standard approach in venous and arterial thromboembolic disease

To determine whether heparin administered by continuous intravenous infusion using a nomogram is superior to a random dosing scheme, we performed a prospective, randomized comparative trial in 161 patients. Patients were prospectively randomized to one of three groups. Group I received an intravenous bolus of 5000 IU of heparin followed by heparin administration according to a modification of a previously published nomogram. Group II patients received a 5000 IU intravenous bolus of heparin followed by continuous intravenous heparin infusion with dosage adjustment at the discretion of the treating physician. Group III patients received a continuous intravenous heparin infusion with dosage adjustments at the discretion of the treating physician without the prior administration of a bolus dose. Activated partial thromboplastin time (APTT) was obtained at baseline, 6 h after each heparin dose adjustment and every morning. The mean percent of each patient's APTTs in the subtherapeutic range (< 50 sec) over the course of treatment was 9% for group I and 24% for groups II and III, p = 0.0001. The three groups had a similar percentage of each patient's APTTs within the therapeutic range (50-80 sec). There was a larger percentage of APTTs > 80 sec in group I (46%) compared to group II (31%) or group III (32%), p = 0.01. There were no clinically recurrent deep venous thrombi or arterial thromboemboli in any of the groups. Two patients had documented pulmonary emboli during heparin therapy (one in group I; one in group II). There was no difference in the complication rates of heparin therapy or the need for blood transfusions among the three groups. Patients randomized to the heparin nomogram (group I) achieved an APTT > 50 sec more frequently than patients in the other two groups. Overall, fewer patients in the nomogram group were subtherapeutic, and, when APTT levels fell in the subtherapeutic range, the nomogram restored APTTs to the therapeutic range faster than the standard methods. The heparin nomogram was clearly more effective as a method of heparin dosing than standard methods of anticoagulation dosing.

Polymorphism of chicken CD8-alpha, but not CD8-beta

We report here the structural basis of CD8 polymorphism in the chicken. Three chicken strains (RPRL Line 7, H.B15.H7, and H.B15. H12) have 14 nucleotide differences in the CD8A cDNA sequence causing eight amino acid replacements in the extracellular part of the molecule. Only two amino acid replacements and four silent mutations were observed in the CD8B cDNA sequence in one (H7) of the strains. Substitutions in CD8alpha were solely responsible for the binding of CD8-specific monoclonal antibodies, as detected by cDNA expression in COS cells. The majority of the amino acid substitutions are located in the immunoglobulin V-like domain and three of the changes (residues 30, 34, and 58) are situated in the putative major histocompatibility complex class I binding CDR1 and CDR2 regions of the chicken CD8alpha. CD8A polymorphism has not been reported in other species and this suggests that CD8A and CD8B have evolved under different selective pressures in the chicken.

The avian chB6 (Bu-1) alloantigen can mediate rapid cell death

The control of cell death is critical in the immune system. T and B lymphocytes must be censored during their development to remove nonfunctional or self-reactive lymphocytes. However, the molecules controlling cell deletion during lymphopoiesis have not been defined. B cells removed from the avian bursa of Fabricius rapidly undergo cell death in culture. We screened bursal B cells with a panel of Abs and lectins to identify molecules affecting their viability. Abs to the chB6 alloantigen caused a rapid loss of cell viability as measured by staining with propidium iodide. ChB6 Abs also cause adhesion between B cells. Transfection of cDNA encoding chB6 reconstituted the allele-specific cell death and adhesion effects in avian cell lines. These effects can be separated by binding cells onto Ab-coated plastic dishes. In these experiments, cells were killed in the absence of cell:cell contact. The ability of chB6 cross-linking to evoke cell aggregation and cell death is also observed when chB6 is expressed in growth factor-dependent mammalian cells. In these cells growth factor can almost completely prevent cell death but not cell aggregation. This suggests that known cell survival stimuli can suppress the cell death brought about by chB6 cross-linking. These results show that chB6 may have an important role in controlling cell survival and/or adhesion during avian B cell development.

The avian chB6 (Bu-1) alloantigen can mediate rapid cell death

The control of cell death is critical in the immune system. T and B lymphocytes must be censored during their development to remove nonfunctional or self-reactive lymphocytes. However, the molecules controlling cell deletion during lymphopoiesis have not been defined. B cells removed from the avian bursa of Fabricius rapidly undergo cell death in culture. We screened bursal B cells with a panel of Abs and lectins to identify molecules affecting their viability. Abs to the chB6 alloantigen caused a rapid loss of cell viability as measured by staining with propidium iodide. ChB6 Abs also cause adhesion between B cells. Transfection of cDNA encoding chB6 reconstituted the allele-specific cell death and adhesion effects in avian cell lines. These effects can be separated by binding cells onto Ab-coated plastic dishes. In these experiments, cells were killed in the absence of cell:cell contact. The ability of chB6 cross-linking to evoke cell aggregation and cell death is also observed when chB6 is expressed in growth factor-dependent mammalian cells. In these cells growth factor can almost completely prevent cell death but not cell aggregation. This suggests that known cell survival stimuli can suppress the cell death brought about by chB6 cross-linking. These results show that chB6 may have an important role in controlling cell survival and/or adhesion during avian B cell development.

The pathological and biological nature of screen-detected breast carcinomas: a morphological and immunohistochemical study

Traditional and immunohistochemical markers of prognosis were examined in 455 mammary carcinomas derived from breast cancer screening and compared with those of 277 carcinomas presenting symptomatically over the same period. Tumours detected by population screening under the U.K. National Health Service Programme do not differ from those detected by other screening projects, but compared with symptomatic cancers, screen-detected cancers are more likely to be in situ and if invasive, to be smaller, of lower grade, and to have invaded vessels, perineural spaces, and lymph nodes less frequently. Tubular and cribriform types are more often represented in screened patients. Immunohistochemical markers which have been proposed as being related to likely tumour behaviour (epidermal growth factor receptor, c-erbB-2 protein, oestrogen and progesterone receptors, cathepsin D, p53, and retinoblastoma protein) do not distinguish screen-detected from 'clinical' cancers. It is concluded that cancers diagnosed at screening do not differ biologically from those presenting clinically, but are the same lesions detected at an earlier stage of their natural history.

Carotid endarterectomy in adults 50 years of age and younger: a retrospective comparative study

PURPOSE

Atherosclerotic carotid artery stenosis (CAS) is the most common cause of stroke in young adults. We retrospectively studied clinical characteristics of premature CAS and the safety and durability of carotid endarterectomy (CEA) in 56 patients 50 years of age or younger (mean, 46.4 years; 34 (60%) males; group I) who underwent primary CEA at the Cleveland Clinic between 1983 and 1993.

METHODS

The patients were identified from the Vascular Surgery Registry and were compared with 202 randomly selected patients 60 years of age and older (mean, 69.3 years; group II) who were frequency-matched by gender and the year of primary CEA. Carotid shunting was used routinely, and the arteriotomy was patched in the majority of cases. Patients were followed-up for mean of 47.2 months (group I) and 46.0 months (group II).

RESULTS

No significant differences were found in the indications for CEA (symptomatic CAS, 49% in group I vs 48% in group II) or the prevalence of diabetes, coronary diseases, and lower extremity arterial disease. Younger adults were more likely to have a history of smoking (93% vs 76%; p = 0.005), hypertension (71% vs 52%; p = 0.006), premature menopause (57% vs 18%; p < 0.001) and had lower levels of high-density lipoprotein cholesterol (p = 0.03). There were no in-hospital deaths. Perioperative strokes in the distribution of the operated artery occurred within 24 hours in one younger patient (1.8%) and in one older patient (0.5%). This was attributed to early carotid thrombosis in the young patient. Major late postoperative neurologic complications were documented in one young patient (1.8%) and six older patients (3%). Patients in group I were at significantly higher risk for recurrent carotid stenosis (risk ratio, 3.1; 95% confidence interval [CI], 1.3 to 7.3; p = 0.010); younger individuals remained at significantly higher risk for recurrent stenosis even after adjusting for smoking and hypertension (risk ratio, 3.7; 95% CI, 1.5 to 9.4; p = 0.006). By life-table analysis, younger adults tended to have a higher rate of late reoperations (p = 0.065).

CONCLUSIONS

CEA can be safely performed in young adults with premature CAS, although younger individuals appear to have higher rates of recurrent carotid stenosis compared with older counterparts.

High incidence of restenosis/reocclusion of stents in the percutaneous treatment of long-segment superficial femoral artery disease after suboptimal angioplasty

PURPOSE

To evaluate the efficacy of intravascular stents used to treat long-segment stenoses and occlusions of the superficial femoral artery (SFA) after suboptimal angioplasty.

METHODS

Fifty-eight limbs in 55 patients who underwent stenting of the SFA were identified from a vascular registry. Indications for stent placement after suboptimal PTA included flow-limiting dissection, residual pressure gradient (>15 mm Hg) or stenosis (>30%), or failure to establish initial patency. Lesion length ranged from 6 to 35 cm (mean, 16.5 cm). Endpoints for primary patency were: restenosis of >50%, reocclusion, or diminution of the postprocedure ankle-brachial index greater than 0.15.

RESULTS

The mean ankle-brachial index improved from 0.48 +/- 0.19 to 0.71 +/- 0.23 (p = 0.001). Primary patency rates by Kaplan-Meier estimates at 1 month, 6 months, and 1 year were 88%, 47%, and 22%, respectively. Secondary patency rates were 94% at 1 month, 59% at 6 months, and 46% at 1 year. The median time to reaching an endpoint of restenosis or reocclusion was 6 months primarily and 9 months secondarily. Clinical improvement at the time of latest follow-up occurred in 56% of patients (mean, 13.8 months). Periprocedural complications occurred in 24.5% of patients with the first intervention. The only factor that favorably influenced outcome was improvement in clinical category after the procedure (p = 0.001).

CONCLUSIONS

There was a high incidence of restenosis and reocclusion with long-segment SFA disease that required stents to achieve initial success. Despite close surveillance and reintervention, anatomic patency at 1 year was poor. However, clinical benefit was maintained in the majority of patients. The outcome was similar in the claudication population compared with those who had limb-threatening ischemia. Percutaneous revascularization of long-segment SFA disease requiring stents should be reserved for patients with critical limb ischemia for which no reasonable surgical alternative exists.

Examination of multidrug resistance in cell lines and primary breast tumours by flow cytometry

The aim of this study was to measure multidrug resistance (MDR) by flow cytometry and quantify the expression of P-glycoprotein (using antibody) glutathione transferase (using alpha-GSTpi antibody) in alpha-JSB-1 and alpha-GSTpi of a series of cell lines and primary breast cancers, and to assess the relationship between these MDR proteins and a selection of oncogene and prognostic markers in breast cancer. Flow cytometry was performed using permeabilised cells stained with fluorescent antibodies using well-established methods. Antibody staining was confirmed for JSB1, but not GSTpi by use of known positive and negative controls. No correlation was seen when comparing the number of molecules of alpha-JSB-1 with alpha-GSTpi (P = 0.1, r2 = 0.4, n = 14) using a selection of cell lines. Examination of 45 breast tumours for expression of JSB-1 and GSTpi revealed a significant association between these two antibodies (P < 0.00001, r2 = 0.5, n = 45). On examining the breast tumours, alpha-JSB-1 showed a positive association with c-erbB-2 (P = 0.003), c-myc (P = 0.0004) and c-jun (P = 0.02) but not ER or EGF-R expression. alpha-GSTpi showed a positive association with c-erbB-2 (P = 0.03) and c-myc (P = 0.0004) but not ER, EGF-R or c-jun. Flow cytometric MDR levels were not related to tumour grade or axillary node status. In solid tumours, a relationship between the two antibodies used has been clearly demonstrated, however, specificity of alpha-GSTpi is questioned. Both antibodies show an association with c-erbB-2, which is associated with poor prognosis and with c-myc which is involved in cell cycling and differentiation. Monitoring MDR markers (Pgp) using this methodology may be useful for evaluation of prognosis in breast cancer.

Concordance of preoperative clinical risk with angiographic severity of coronary artery disease in patients undergoing vascular surgery

BACKGROUND

Preoperative clinical indexes to stratify cardiac risk have not been validated angiographically. Our aims were to determine the concordance of clinical risk with severity of coronary stenosis and to develop and validate a preoperative clinical index to exclude the presence of significant coronary stenosis.

METHODS AND RESULTS

We carried out a prospective study of 878 consecutive patients (including the derivation and validation sets). "Severe" stenosis was defined as three-vessel (> or = 50% stenosis in each), two-vessel (> or = 50% stenosis in one when the other is > or = 70% stenosis of the left anterior descending), or left main disease (> or = 50%); "critical" stenosis was three-vessel (> or = 70% stenosis in each) and/or left main stenosis > or = 70%. A preoperative clinical index (diabetes mellitus, prior myocardial infarction, angina, age > 70 years, congestive heart failure) was used to stratify patients. A gradient of risk for severe stenosis was seen with increasing numbers of clinical markers. The following prediction rules were developed: The absence of severe coronary stenoses can be predicted with a positive predictive value of 96% for patients who have no (1) history of diabetes, (2) prior angina, (3) previous myocardial infarction, or (4) history of congestive heart failure. The absence of critical coronary stenoses can be predicted with a positive predictive value of 94% for those who have no (1) prior angina, (2) previous myocardial infarction, or (3) history of congestive heart failure.

CONCLUSIONS

By reliably identifying a large proportion of patients with a low likelihood of significant stenoses, these prediction rules can help to substantially reduce healthcare costs associated with preoperative cardiac risk assessment for noncardiac surgery.

Angiographic correlates of cardiac death and myocardial infarction complicating major nonthoracic vascular surgery

In a case-control study of 63 patients undergoing major nonthoracic vascular surgery with prior cardiac catheterization, we found total coronary occlusion serving viable myocardium and "nonobstructive" lesions to be the most common proximate cause of perioperative myocardial infarction or death. The extent of coronary disease by several measures was significantly correlated with adverse outcome, and prior bypass surgery appeared to be protective.

Chicken B-cell marker chB6 (Bu-1) is a highly glycosylated protein of unique structure

The chB6 molecule is expressed on chicken B cells throughout most of their development, as well as on some non-lymphoid cells. It has long been used as an allotypic marker in important studies of B-cell development, though its function is unknown. We isolated a chB6 cDNA by expression cloning and sequenced two further alleles following polymerase chain reaction amplification. The results show that chB6 is a typical type I transmembrane protein, highly glycosylated in the extracellular region and carrying a large intracellular region. It has no recognizable similarity to known mammalian molecules and thus represents a unique B-cell marker. Its presence in chickens may be related to differences in the properties of B-cell development between chickens and mammalian species. The sequences of the different alleles of this gene revealed a higher level of polymorphism than expected. A restriction fragment length polymorphism linked to the CHB6 gene has been used to determine its location on the linkage map of the chicken genome, which will allow the definitive evaluation of reported associations with disease resistance.