Nonmajor histocompatibility complex alloantigen effects on the fate of Rous sarcomas

Rous sarcoma virus-induced tumor outcome is controlled by the MHC (B). Additional data, using controlled segregation in families, has indicated non-MHC effects as well, but few studies have focused on blood groups other than the B complex. Segregating combinations of genes encoding erythrocyte (Ea) alloantigen systems A, C, D, E, H, I, P, and L in B2B5 and B5B5 MHC (B) backgrounds were examined for their effects on Rous sarcomas. Six-week-old chickens were inoculated in the wing-web with 30 pfu of Rous sarcoma virus (RSV). Tumors were scored six times over a 10-wk period. A tumor profile index (TPI) was assigned to each chicken based on the six tumor size scores. Response was evaluated using tumor size at each measurement period, TPI, and mortality. The genotypes of Ea systems A, C, D, E, H, I, and P had no significant effect on any parameter in either B complex population. The Ea-L system had an effect on Rous sarcomas in the B2B5 intermediate responders and B5B5 progressors. Tumor size, TPI, and mortality were all significantly lower in B2B5 L1L1 chickens than in B2B5 L1L2 chickens. Mortality was lower in the B5B5 L1L1 birds than in B5B5 L1L2 chickens. It appears that the Ea-L system, or one closely linked, is acting in a manner independent of the B complex in response to RSV challenge.

Decreased cerebral emboli during distal aortic arch cannulation: a randomized clinical trial

BACKGROUND

Cerebral emboli occur during cardiopulmonary bypass and are a principal cause of postoperative neurologic dysfunction. We hypothesized that arterial cannulation of the distal aortic arch, with placement of the cannula tip beyond the left subclavian artery, will result in fewer cerebral microemboli than conventional cannulation of the ascending aorta.

METHODS

Patients undergoing coronary bypass surgery with a single crossclamp technique were randomized to receive cannulation of the distal aortic arch (n = 17) or standard cannulation of the ascending aorta (control group, n = 17). Trendelenburg positioning was used whenever possible. Cerebral emboli were quantified by continuous transcranial Doppler monitoring of the middle cerebral artery.

RESULTS

Baseline demographics were similar for the 2 groups of patients, including cardiopulmonary bypass and crossclamp times. Cerebral microemboli were detected during cardiopulmonary bypass in all patients, with a range of 17 to 627 emboli. The total number of detected emboli was lower in the arch cannulation group (152 +/- 33, mean +/- standard error of the mean) than in the conventional cannulation group (249 +/- 35, P =.04). Embolization rates were lower in distal arch patients than in control patients during cardiopulmonary bypass (2.0 +/- 0.3 vs 4.2 +/- 0.9 per minute, respectively, P =.03). Reduction in cerebral emboli by distal arch cannulation was most pronounced during perfusionist interventions.

CONCLUSIONS

Cannulation of the distal aortic arch results in less cerebral microembolism than conventional cannulation of the ascending aorta. Provided it is performed safely, distal arch cannulation may be an important surgical option for patients with severe atherosclerosis of the ascending aorta.

Cerebral microemboli during cardiopulmonary bypass: increased emboli during perfusionist interventions

BACKGROUND

Microemboli to the cerebral circulation occur during cardiopulmonary bypass (CPB) and can contribute to postoperative neurologic dysfunction. Cerebral microemboli are known to occur during specific surgical interventions, but the source of a large proportion of emboli remains unexplained. We investigated whether interventions by the perfusionist could account for the appearance of cerebral microemboli.

METHODS

Transcranial Doppler ultrasonography was used to continuously monitor the middle cerebral artery of 18 patients undergoing coronary artery bypass grafting. The CPB circuit consisted of a softshell venous reservoir, a hollow-fiber membrane oxygenator, and a 32-microm arterial filter. The mean embolic rate was calculated for three time periods: (1) during surgical interventions (aortic cannulation and decannulation, cross-clamp application and removal, CPB start and end, and start of cardiac ejection); (2) during perfusionist interventions (blood sampling and drug administration into the venous reservoir); and (3) during baseline (all other time periods during CPB).

RESULTS

Microemboli were detected in all patients (mean +/- standard deviation, 207+/-142 per patient, median, 132). The number of emboli per minute was significantly (p < 0.001) higher during perfusionist interventions (6.9+/-4.5) than during surgical interventions (1.5+/-1.5) or during baseline (0.4+/-0.5). Drug administration resulted in a higher embolic rate than blood sampling.

CONCLUSIONS

Interventions by the perfusionist account for a large proportion of previously unexplained cerebral microemboli during CPB. These emboli likely represent air bubbles that are not eliminated by the arterial line filter. Although further studies of additional types of CPB circuits are required, we believe that air in the venous reservoir should be avoided whenever possible to minimize the risk of neurologic injury.

Cardiovascular and behavioral response to social confrontation: measuring real-life stress in the laboratory

Laboratory investigations of cardiovascular reactivity to mental stress often ignore concomitant differences in cognitive, affective, and behavioral responses that are commonly observed among study participants. To provide a more systematic laboratory methodology to examine relations among cardiovascular, behavioral, and self-report measures of cognitive and affective responses to stress, we developed and tested a social confrontation procedure involving standardized interactions during two scenes. Results of three investigations are presented to illustrate the utility of the social confrontation procedure. In the first two studies, this multidimensional assessment strategy produced results which may foster research projects that bridge separate areas of psychological inquiry. In one application, persons with hypertensive parents, in contrast to persons with normotensive parents, exhibited characteristic negative behavioral responses during both interactions as well as the more commonly-observed exaggerated blood pressure reactions. In the other study, students from less functional families (regarding cohesion and adaptability) were shown to exhibit exaggerated blood pressure reactions in addition to their commonly-reported negative cognitive and behavioral coping styles. Finally, a third study examined how a simple instructional set regarding the expression or suppression of anger influenced participants' responses. Significant differences were observed across response domains, with anger expression resulting in a more intense response than anger suppression. In sum, the social confrontation procedure represents an important methodological development for exploring the relation between response domains, the relation between cardiovascular response to stress and psychosocial risk for cardiovascular disease, and the physiological and behavioral distinction between anger expression and anger suppression.

Calcium dependency of interleukin-1 secretion by a chicken macrophage cell line

The role of calcium in transducing the signal for interleukin-1 (IL-1) secretion was examined in the MQ-NCSU chicken macrophage cell line. Cells were maintained in RPMI 1640 medium supplemented with 5% chicken serum and antibiotic-antimycotic solution at 40 C and 5% CO2. The effects of stimulation with lipopolysaccharide (LPS), calcium ionophore A23187, or a combination of both on IL-1 secretion were examined. Calcium ionophore A23187 did not replace LPS in MQ-NCSU stimulation but the LPS + A23187 combination stimulated more IL-1 than ionophore alone in these cells. The combination of LPS and ionophore did not increase IL-1 secretion above the levels observed with LPS alone. No synergistic effects between LPS and A23187 were evident. In order to demonstrate that IL-1 secretion by the MQ-NCSU cells is a calcium-dependent process, ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA) was used to chelate free calcium in the cultures. Incorporation of 5 mM EGTA in the cultures lowered IL-1 stimulated by LPS + A23187 to control levels. Addition of 5 mM CaC12 to EGTA-suppressed cultures restored IL-1 secretion. These results indicate that the calcium ionophore, A23187, augments IL-1 secretion by LPS-stimulated MQ-NCSU macrophages and that IL-1 secretion by these cells is a calcium-dependent process.

B-complex associated immunity to Salmonella enteritidis challenge in congenic chickens

Six trials were conducted during which a total of 12 congenic lines (University of California-Davis, UCD) homozygous for various B-complex haplotypes, were challenged as neonates by intraperitoneal injection with either of two isolates of Salmonella enteritidis. Because these B haplotypes were expressed on a common genetic background (highly inbred Line UCD 003), and mortality differences among lines were statistically significant in three of the six trials, and morbidity (body weight) differences were significant in another trial; it is suggested that B-complex alleles affect the degree of immunity to these isolates. When all lines and trials were compared, line 342 (BC/BC) emerged as particularly resistant, whereas lines 253 (B18/B18) and 254 (B15/B15) were more susceptible. The remainder of the lines were of neutral (intermediate) susceptibility. Sex did not appear to influence the results of the challenge, but more resistance was observed with an increase in the age at inoculation. Although the mechanism that determined this resistance is unknown it was present as early as 3 d of age, and it is suggested that complement proteins, which have a known role in protection from bacterial infections, and are encoded by genes located within the B-complex, or acute phase proteins, may account for these observations. The results provide additional evidence for the importance of the B-complex in determining immunity to Salmonella.

Ropinirole for the treatment of early Parkinson disease: a 12-month experience. Ropinirole Study Group

OBJECTIVE

To evaluate ropinirole hydrochloride as dopaminergic monotherapy in patients with early Parkinson disease.

DESIGN

A 6-month extension of a double-blind, placebo-controlled study.

SETTING

Ambulatory care at 22 different sites in the United States.

PATIENTS

Patients who successfully completed the initial 6-month study could enter the 6-month extension study (ropinirole, n = 70; placebo, n = 77).

INTERVENTION

Use of ropinirole or placebo therapy.

MAIN OUTCOME MEASURES

The efficacy variables were the number of patients who successfully completed the 12-month study and did not require supplemental levodopa, the number of patients requiring supplemental levodopa, and the proportion of patients having an insufficient therapeutic response.

RESULTS

Significantly fewer ropinirole-treated patients met criteria for insufficient therapeutic response (23 [19.8%] of 116) or required the initiation of levodopa therapy (22 [19%] of 116) compared with placebo-treated patients (60 [48%] of 125 patients for insufficient therapeutic response; 57 [45.6%] of 125 patients for additional levodopa). Significantly more ropinirole-treated patients (51 [44.0%] of 116) successfully completed the 12-month study and did not require supplemental levodopa compared with placebo-treated patients (28 [22.4%] of 125). The incidence of adverse experiences and patient withdrawals was low.

CONCLUSION

Ropinirole was effective and well tolerated as monotherapy for 12 months in patients with early Parkinson disease.

Students in compensatory education programs: analysis of scores on performance assessments for the Iowa Test of Basic Skills

Analysis of Mathematics and Language Arts scores for 11,438 fourth- and 8,972 seventh-grade students in compensatory education programs on the performance assessments for the Iowa Test of Basic Skills indicated the students performed poorly, particularly in mathematics.

Abnormal proinsulin levels in thyroid dysfunction measured by a sensitive proinsulin immunochemiluminoassay

Abnormalities of carbohydrate metabolism in hyperthyroid patients have been long noted. Elevated proinsulin level is considered as an early marker of B-cell impairment. Proinsulin levels in hyperthyroid patients decreased after antithyroid drug therapy. However, proinsulin in hypothyroid patients was only rarely reported, and the difference was only demonstrated after glucose stimulation-there was a greater response of proinsulin secretion after thyroxine therapy-and the basal fasting proinsulin level was not different after therapy. One of the reasons might be that the assay was not sensitive enough to detect the change of basal proinsulin levels in patients with hypothyroidism after therapy. A newly developed immunochemiluminometric assay of proinsulin was used to demonstrate that the suppressed proinsulin level increased after thyroxine therapy in hypothyroid patients (4.2 +/- 2.4 vs. 10.0 +/- 5.6 pmol/L, p < 0.05; n = 7). On the other hand, our study also confirmed that the proinsulin levels decreased in hyperthyroid patients after antithyroid therapy by methimazole (27.8 +/- 26.0 vs. 15.8 +/- 15.7 pmol/L, p < 0.05; n = 12). In conclusion, proinsulin increased in hypothyroid patients after thyroxine therapy and decreased in hyperthyroid patients after methimazole therapy. The results demonstrated there is a high correlation between thyroid function and B-cell function in hypothyroid as well as hyperthyroid patients.

The influence of substratum topography on bacterial adhesion to polymethyl methacrylate

The effect of substratum roughness on the adhesion of Pseudomonas aeruginosa and Staphylococcus epidermidis was investigated using PMMA. A small increase in Ra values (0.04-1.24 microm) resulted in a significant increase (P<0.05) in bacterial attachment. Subsequent increases in surface roughness (Ra=1.86-7.89 microm) resulted in a decrease in adhesion, although adhesion was still higher than to the smooth surface. When the PMMA surfaces were coated with protein (bovine serum albumin), no difference (P<0.05) could be determined in the amount of protein adsorbed, irrespective of surface topography. However, the influence of the underlying topography on adhesion was still evident. Substratum topography is an important parameter affecting bacterial adhesion to surfaces.

Modulation of bacterial adhesion to hydrogel contact lenses by albumin

PURPOSE

The purpose of this investigation was to measure the abilities of Pseudomonas aeruginosa and Staphylococcus epidermidis strains to adhere to two hydrogel lens materials and measure the effect of a protein-coated surface on the number of adhered bacteria.

METHODS

Proteins absorbed to contact lenses during sleep were extracted, subjected to sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), and probed for the presence of albumin. Bacterial adhesion was measured by counting bacteria adherent to contact lenses coated in vitro in increasing concentrations of albumin, examining the ability of albumin in solution to prevent adhesion to albumin-coated lenses, and examining the topography of bacterial adhesion by electron microscopy.

RESULTS

Albumin adsorbed to lenses during overnight wear. In vitro studies demonstrated that Polymacon lenses adsorbed more albumin than Etafilcon A lenses. In general, the numbers of adherent bacteria increased with increasing concentration of albumin. Bacteria adhered in higher numbers to Polymacon lenses than Etafilcon A (p < 0.05). P. aeruginosa showed an increased adhesion as the amount of albumin on Etafilcon A lenses increased. There was a decrease in numbers of bacteria adhering per milligram of albumin as the level of albumin increased on Polymacon lenses. Cells tended to adhere to "deposits" on albumin-coated lenses.

DISCUSSION

Albumin adsorbed onto the surface of contact lenses modulated the ability of P. aeruginosa and S. epidermidis to adhere. P. aeruginosa is commonly associated with contact lens-associated microbial keratitis, where bacterial adhesion to contact lenses is believed to be an important first step in the pathogenesis of the disease.

Increased parathyroid hormone-related peptide in patients with hypercalcemia associated with islet cell carcinoma

OBJECTIVE

To report the high prevalence of increased parathyroid hormone-related peptide (PTHrP) in patients with islet cell carcinoma and associated hypercalcemia.

DESIGN

We conducted a retrospective study of PTHrP levels in patients with hypercalcemia and eucalcemia associated with islet cell carcinoma and compared these findings with those in healthy subjects.

MATERIAL AND METHODS

Using a sensitive PTHrP immunochemiluminometric assay, we measured PTHrP levels in 17 patients with islet cell carcinoma and 110 healthy subjects. The differences between PTHrP levels in patients with normal and those with high serum calcium concentrations were analyzed statistically.

RESULTS

PTHrP levels were significantly higher (P < 0.01) in 10 patients with hypercalcemia and islet cell carcinoma (median, 14.0 pmol/L; range, undetectable to 40.1) than in 7 patients with eucalcemia and islet cell carcinoma (median, undetectable; range, undetectable to 1.3 pmol/L) or in the 110 healthy subjects (median, undetectable; range, undetectable to 4.2 pmol/L). The range of increased PTHrP levels in hypercalcemic islet cell carcinoma was 2 to 20 times the upper normal limit (2.0 pmol/L). Decreased PTHrP and serum calcium and increased parathyroid hormone levels were demonstrated in two patients after effective therapy. For all seven eucalcemic patients with islet cell carcinoma, PTHrP levels did not differ significantly from those in healthy subjects.

CONCLUSION

PTHrP levels are increased in a substantial proportion of patients with hypercalcemia and islet cell carcinoma and seem to decrease after treatment of the underlying tumor. Measurement of PTHrP levels may be useful for confirming the diagnosis of hypercalcemia associated with malignant disease and for monitoring of therapy.

Parathyroid-hormone-related peptide immunochemiluminometric assay. Developed with polyclonal antisera produced from a single animal

An immunochemiluminometric assay of parathyroid-hormone-related peptide (PTHrP) was developed with purified antisera produced from a single goat immunized with (1-86) PTHrP. One batch of purified antibodies was labeled with acridinium ester used as tracer antibodies; a second batch of the purified antibodies was immobilized onto plastic bead. Sensitivity of the assay was 0.1 pmol/L. The assay had no cross-reactivity with PTH. Seventy-five percent of healthy individuals had undetectable PTHrP (mean +/- S.D. were 0.73 pmol/L +/- 0.6; n = 110). The 95 percent upper reference limit was 2.0 pmol/L. Five of the seven patients with humoral hypercalcemia associated with malignancy (HHM) of solid-tumor had PTHrP greater than 2.0 pmol/L. The test efficacy in detecting HHM was 71 percent, which is similar to previous extraction radioimmunoassay (RIA) or immunoradiometric assay (IRMA). The new assay lowered the detection limit to 0.1 pmol/L, which is a great improvement from that of RIA at 2.0 pmol/L and IRMA at 1.0 pmol/L; however; it did-not improve the test efficacy in detecting patients with HHM. It may indicate the patients with HHM only have elevated plasma PTHrP in 70 percent of them. Technically, the method can be used as a model to develop chemiluminescent esoteric test for research or reference laboratories.

Ropinirole for the treatment of early Parkinson's disease. The Ropinirole Study Group

A prospective, randomized, placebo-controlled, double-blind, parallel-group, 6-month study assessed the efficacy and safety of ropinirole, a nonergoline D2-dopamine agonist, in patients with early Parkinson's disease (n = 241; Hoehn & Yahr stages I to III) with limited or no prior dopaminergic therapy. Patients (mean age, 62.8 years), stratified by concomitant use of selegiline, were randomized to ropinirole (n = 116) or placebo (n = 125). The starting dose of ropinirole was 0.25 mg tid with titration to at least 1.5 mg tid (maximum dose, 8 mg tid). Primary efficacy endpoint was the percentage improvement in Unified Parkinson's Disease Rating Scale (UPDRS) motor score. Ropinirole-treated patients had a significantly greater percentage improvement in UPDRS motor score than patients who received placebo (+24% vs -3%; p < 0.001). Ropinirole was well tolerated and patient withdrawals were infrequent. Most adverse experiences were related to peripheral dopaminergic activity. Ropinirole monotherapy is an effective and well-tolerated therapeutic option for treatment of early Parkinson's disease.

Resistance, susceptibility, and immunity to Eimeria tenella in major histocompatibility (B) complex congenic lines

The major histocompatibility (B) complex influence on resistance, susceptibility, and immunity to Eimeria tenella was examined in UCD B complex congenic chicken lines. In Experiment 1, 6-wk-old chicks from 12 UCD congenic lines were weighed and assigned to either challenge or control groups. The challenge group received a dose of 10,000 E. tenella oocysts. Response to challenge was evaluated by body weight gain and cecal lesion scores. Cecal lesion scores in B3B3 chickens were significantly lower than those of all other genotypes. Genotype B2B2 had the highest lesion scores, which were significantly different from the lesion scores calculated for B3B3, B18B18, and B21B21 chickens but were not significantly different from B14B14, B15B15, B17B17, B19B19, B24B24, BCBC, BJBJ, and BQBQ genotypes. The B21B21 chickens had significantly lower lesion scores than B2B2, B14B14, and BCBC chickens. No other significant lesion score differences were found among the remaining lines. The highest weight gain found in B19B19 chickens was significantly different from that of B3B3, B14B14, B15B15, B17B17, B18B18, B24B24, and BCBC chickens. The B15B15 chickens had the lowest weight gain, which was significantly different from that of B2B2, B19B19, B21B21, B24B24, BJBJ, and BQBQ chickens. Experiment 2 tested the immune response to E. tenella after low dose oocyst immunization. Chicks from 10 UCD 003 congenic lines were divided into three groups: control, challenge, and immune. At 5 wk of age, the immune group was immunized with 500 E. tenella oocysts for 5 consecutive d. Fourteen days after the last immunization all chicks were weighed, and 10,000 E. tenella oocysts were administered to the challenge and immune groups. Significant lesion score differences existed among all three treatments: control (0), immune (2.14 +/- 0.1); challenge (3.13 +/- 0.1). Among immune birds, B3B3 and BQBQ chickens had significantly lower lesion scores than B19B19, B24B24, B14B14, and B2B2 chickens. Neither B19B19 nor B24B24 chickens were well-protected, as indicated by their higher lesion scores. No significant differences in weight gain were found in immune birds. The B complex affected resistance and susceptibility as well as the immune response to E. tenella. Cecal lesion scores following challenge in naive birds or after immunization were influenced by the B complex, whereas weight gain was affected in naive birds only. These effects may be manifested through differences in immune competence at the time of challenge or immunization, the amount of parasite antigen production, or the threshold doses for effective immunization.

Characterization of immune response to Eimeria tenella antigens in a natural immunity model with hosts which differ serologically at the B locus of the major histocompatibility complex

A model to simulate natural immunity to Eimeria tenella was developed in three chicken lines which differ at the B locus of the major histocompatibility complex. Homozygous, 1-day-old chicks of the B19B19, B24B24, or B30B30 genotype were trickle immunized by being orally fed a small infectious dose of E. tenella oocysts for 5 consecutive days. These naturally exposed birds were then challenged at different times between 5 and 24 days after the final dose, and the level of protection was assessed 6 days after challenge, using body weight gain and intestinal lesion scores. The duration of immunity in naturally exposed birds differed among the major histocompatibility complex lines. Trickle immunization of the B19B19 haplotype afforded the longest and strongest level of protection compared to the other two haplotypes tested. In addition, in vitro splenic and peripheral blood lymphocyte proliferative responses in trickle-immunized birds were measured against sporozoite, merozoite, and tissue culture-derived E. tenella parasite antigens isolated from the recently described SB-CEV-1/F7 established cell line. The lymphocytes obtained from B19B19 birds trickle immunized responded in vitro to the E. tenella-infected SB-CEV-1/F7 tissue culture-derived parasite antigen. Furthermore, antigen-specific immune responses appeared earlier in immune, challenged B19B19 birds than in their naive, challenged counterparts. The development of a model simulating natural immunization will serve as a foundation to further characterize both humoral and cell-mediated responses to E. tenella tissue culture-derived parasite antigens and to better understand host protective immune responses to avian coccidiosis.

Governance of integrated delivery systems/networks: a stakeholder approach

The health care environment is complex and turbulent, and traditional governance forms face many challenges. As integrated delivery systems/networks are formed, governance structures must be responsive to both internal and external stakeholders. Both internal efficiencies and socially responsible actions are required of these relatively new organizational forms. To meet these needs, a two-tier governance structure is presented that consists of overarching and facilitating boards.

Sequence variation in the src gene product affects metastasis formation: the central, but not exclusive, role of the tumor immune response

Sequence variation in the src gene product could, in principle, influence metastasis formation through either of 2 effects: an alteration in tumor antigenicity or a non-immune-mediated change in one or more src-associated functions. Our present results establish that both mechanisms underlie the difference in relative levels of metastasis formation induced by the v-src vs. the c-src(527) oncogene. A point that emerges from this analysis is the segregation, within a chicken line genotypically uniform at the major histocompatibility (B) complex (MHC), of a phenotype defined by strong resistance to secondary v-src-induced tumor challenge. The pattern of segregation is consonant with the possibility that a gene unlinked to the MHC governs immune response levels to v-src-encoded tumor antigen.

Eliminating inappropriate classroom behavior using a DRO schedule: a preliminary study

The purpose of this study was to eliminate out-of-seat behavior of a 14-yr.-old boy with learning disabilities using a single-subject design. Based on functional analysis, a Differential Reinforcement of Other Behavior interval schedule was used to eliminate an inappropriate behavior. During baseline, an average of 15 out-of-seat behavior problems were recorded. After 4 wk. of intervention, the inappropriate out-of-seat behavior was eliminated and on-task behavior improved.

Assignment of Rfp-Y to the chicken major histocompatibility complex/NOR microchromosome and evidence for high-frequency recombination associated with the nucleolar organizer region

Rfp-Y is a second region in the genome of the chicken containing major histocompatibility complex (MHC) class I and II genes. Haplotypes of Rfp-Y assort independently from haplotypes of the B system, a region known to function as a MHC and to be located on chromosome 16 (a microchromosome) with the single nucleolar organizer region (NOR) in the chicken genome. Linkage mapping with reference populations failed to reveal the location of Rfp-Y, leaving Rfp-Y unlinked in a map containing >400 markers. A possible location of Rfp-Y became apparent in studies of chickens trisomic for chromosome 16 when it was noted that the intensity of restriction fragments associated with Rfp-Y increased with increasing copy number of chromosome 16. Further evidence that Rfp-Y might be located on chromosome 16 was obtained when individuals trisomic for chromosome 16 were found to transmit three Rfp-Y haplotypes. Finally, mapping of cosmid cluster III of the molecular map of chicken MHC genes (containing a MHC class II gene and two rRNA genes) to Rfp-Y validated the assignment of Rfp-Y to the MHC/NOR microchromosome. A genetic map can now be drawn for a portion of chicken chromosome 16 with Rfp-Y, encompassing two MHC class I and three MHC class II genes, separated from the B system by a region containing the NOR and exhibiting highly frequent recombination.