MicroCT Imaging of Heart Valve Tissue in Fluid.

BACKGROUND: Heart valve computational models require high quality geometric input data, commonly obtained using micro-computed tomography. Whether in the open or closed configuration, most studies utilize dry valves, which poses significant challenges including gravitational and surface tension effects along with desiccation induced mechanical changes. OBJECTIVE: These challenges are overcome by scanning in a stress-free configuration in fluid. Utilizing fluid backgrounds however reduces overall contrast due to the similar density of fluid and tissue. METHODS: The work presented here demonstrates imaging of the mitral valve by utilizing an iodine-based staining solution to improve the contrast of valve tissue against a fluid background and investigates the role of stain time and concentration. RESULTS: It is determined that an Olea europaea oil bath with a relatively high concentration, short stain time approach produces high quality imagery suitable for creating accurate 3D renderings. CONCLUSIONS: Micro-CT scanning of heart valves in fluid is shown to be feasible using iodine staining techniques.

Occurrence of restricted suppressor T-cell activity in man.

Blood leukocytes from an immunologically hyporesponsive patient with urinary bladder carcinoma were found to be deficient in their ability to stimulate 3 of 27 responder leukocyte preparations from normal individuals in one-way mixed leukocyte culture (MLC). The patient's T-depleted leukocytes, however, functioned adequately as stimulator cells. T-enriched lymphocytes from this patient suppressed the MLC responsiveness of those three normals but not the responsiveness of other normals. The patient's cells suppressed the MLC responsiveness of only one of each of the parents of two of the normals who could be suppressed by the patient's leukocytes suggesting a possible genetic restriction to this suppressor cell activity.

Ly phenotype of cytotoxic T cells for syngeneic tumor.

Our present and previous findings may be summarized as follows: The phenotype of C57BL/6 (B6) cytotoxic cells for allogeneic target cells is Thy-1+, Ly-1- Ly-2/3+, MSLA+, and Ig-. the phenotype of B6 cytotoxic cells for syngeneic tumor cells is Thy-1+, Ly-1+, Ly-2/3+, MSLA+, and Ig-. The phenotype of B6 cytotoxic cells for syngeneic tumor cells is Thy-1+, Ly-1+, Ly-2/3+, MSLA+, AND Ig-. Thus, differences in Ly phenotype appear to be exhibited not only by cytotoxic T cells as opposed to helper T cells, but also within subcategories of cytotoxic T cells.

Expression of T-cell differentiation antigens on effector cells in cell-mediated cytotoxicity in vitro. Evidence for functional heterogeneity related to the surface phenotype of T cells.

The cell-mediated cytotoxicity (CMC) of nonadherent cells from the peritoneal cavity (NAPC) of alloimmunized mice can be measured by the [3H]proline microassay. The exhibition of thymus-derived (T) cell antigens on these killer cells was studied by incubating them with the relevant T-cell antisera and complement (C), under optimal conditions for lysis, before performance of the CMC assay. Under these conditions, the following T-cell antigens were demonstrable on the killer population in terms of percent reduction in CMC by the respective antisera: (a) Thy-1.1 (83%) and Thy-1.2 (100%), (b) MSLA (86%), (c) NTA-RA (a T-cell antigen recognized by naturally occurring autoantibody of NZB mice) (62%), (d) Ly1.1 )58%, (e) Ly-2.1 (11%; considered a marginal result) and Ly-2.2 (63%), and (f) Ly-3.2 (77%). The following were not demonstrable: (g) TL, and (h) Ly-1.2. (i) The antigen Ly-3.1 was not studied. Omission of C deprived all T-cell antisera tested of their capacity to suppress CMC, indicating that the cell components recognized by such antisera may perform no direct function in CMC. On the assumption that all Ly+ cells are Thy-1+, it is clear that the T-cell members of the immune NAPC population must be heterogenous. This follows from the fact that the proportions of T cells lysed by different Ly antisera did not correspond with ensuing degree of loss of CMC capacity. The extremes were represented by anti-Ly-1.2 (74% Thy-1+ cells lysed, but no reduction in CMC) and Ly-3.2 (54% Thy-1+ cells lysed, with 77% reduction in CMC). From this initial survey it appears that the C57BL/6 mice killer T-cell population active in CMC in vitro is relatively rich in surface antigens of the Ly-2/Ly-3 category and relatively poor in representation of the Ly-1 surface antigens. It remains to be seen whether this killer cell phenotype, poor in Ly-1 and rich in Ly-2/Ly-3, is characteristic of the mouse generally. From these results it appears that subsets of T cells with different immunological functions may exhibit qualitative or quantitative differences in surface antigens specified by different Ly loci; this will be easier to assess in the future when the results of experiments with the same Ly antisera but dealing with T-cell functions other than CMC become available.

Evidence for increased somatic cell mutations at the glycophorin A locus in atomic bomb survivors.

A recently developed assay for somatic cell mutations was used to study survivors of the atomic bomb at Hiroshima. This assay measures the frequency of variant erythrocytes produced by erythroid precursor cells with mutations that result in a loss of gene expression at the polymorphic glycophorin A (GPA) locus. Significant linear relations between variant frequency (VF) and radiation exposure were observed for three different variant cell phenotypes. The spontaneous and induced VFs agree with previous measurements of radiation-induced mutagenesis in other systems; this evidence supports a mutational origin for variant cells characterized by a loss of GPA expression and suggests that the GPA assay system may provide a cumulative dosimeter of past radiation exposures. VFs for some survivors differ dramatically from the calculated dose response, and these deviations appear to result primarily from statistical fluctuations in the number of mutations in the stem-cell pool. These fluctuations allow one to estimate the number of long-lived hemopoietic stem cells in humans.

Impact of motivational interviewing on engagement in a parent-exclusive paediatric obesity intervention: randomized controlled trial of NOURISH+MI.

BACKGROUND: Attrition and treatment adherence are notorious challenges in paediatric obesity interventions. OBJECTIVE: To evaluate if brief, pretreatment motivational interviewing (MI) can improve retention (at baseline, post-assessment and follow-up assessment) and adherence (i.e. attendance) in a parent-exclusive paediatric obesity intervention. METHODS: MI was implemented with parents as an adjunct to a larger randomized controlled trial of Nourishing Our Understanding of Role-modeling to Improve Support and Health (NOURISH+ ), a parent intervention for children with overweight ages 5-11 years. Parents (N = 112) were randomized to receive two MI sessions (one telephone and one in person) or reminder calls. RESULTS: Parents (91% women; 52% African American) who completed one telephone MI session were more likely to attend baseline (74%) compared with parents who received reminder calls only (53%, p < .001). After a second MI session, there were no group differences in treatment initiation (p > .05). Treatment attendance, post or 4-month follow-up assessment completion did not differ between conditions (p > .05). CONCLUSION: One MI session implemented prior to treatment can improve baseline attendance; a second MI session did not enhance these effects. A single-session telephone-based MI pretreatment might be a cost and time-effective strategy to enhance recruitment efforts. Further strategies to address retention and treatment attendance are needed.

Measurement and modelling of radioxenon plumes in the Ottawa Valley.

Since 2001 a real-time radiation monitoring network of Canadian nuclear facilities and major population centres has been implemented for response to nuclear incidents including a possible terrorist attack. Unshielded NaI(Tl) spectroscopic detectors are employed to measure gamma radiation from airborne radioactivity and radioactivity deposited on the ground. These detectors are composed of a standard 3''x3'' cylindrical NaI(Tl) spectrometers with data storage and integrated telemetry. Some of the detectors have been deployed in the Ottawa Valley near Chalk River Laboratories and Ottawa, which has a complex radioxenon environment due to the proximity of nuclear power reactors, and medical isotope facilities. Although not a health threat, these releases have provided an opportunity for the Canadian Meteorological Centre and the Commissariat à l'Energie Atomique to validate their meteorological models. The meteorological models of the two organizations are in good agreement on the origin and the source terms of these releases.

Impact of motivational interviewing on outcomes of an adolescent obesity treatment: results from the MI Values randomized controlled pilot trial.

The aim of this study is to examine outcomes from MI Values, a motivational interviewing (MI) intervention implemented adjunctive to obesity treatment. Adolescents (n = 99; 73% African American; 74% female; mean body mass index [BMI] percentile = 98.9 ± 1.2) were randomized to receive two MI sessions or education control. All adolescents participated in structured behavioural weight management treatment. Baseline, 3- and 6-month assessments of anthropometrics, dietary intake and physical activity were obtained. Both groups had significant reductions in BMI z-scores and energy intake and increased physical activity at 3 and 6 months (P < 0.05). MI participants reported greater reductions in 3-month energy intake compared with controls. Participation in MI is associated with reduction in energy intake, consistent with better adherence to dietitian visits previously reported from MI Values. MI might be an effective adjunct to adolescent obesity treatment; future research is needed to determine if motivational interviewing can enhance BMI outcomes, via greater adherence to behavioural intervention.

Cytotoxic reactions of murine lymphoid cells studied with a tritiated proline microcytotoxicity test.

A lymphocyte cytotoxicity (CTX) test with 3-H-proline-prelabeled target cells was used to detect the immune response of murine lymphoid cells to H-2 and tumor antigens. The specificity of the reaction was determined by simultaneous tests on unrelated target cells and, for reactions directed against H-2 antigens, by blocking experiments with alloantiserum directed against the H-2 antigens of the target cells. After a single intraperitoneal (ip) injection of allogeneic spleen cells, CTX of unfractionated peritoneal cellswas strong, with a sharp peak on day 5. Repeated ip immunization markedly increased the CTX of unfractionated peritoneal cells. The reaction was strongest when the test was done at 37 degrees C. Sometimes CTX should be detected after as little as 6 hours' incubation. CTX depended primarily on the absolute number of effector or target cells per area rather than on the ratio of effector to target cells. Both nonadherent and adherent peritoneal cells destroyed target cells specifically. The CTX of nonadherent peritoneal cells was increased by 2-mercaptoethanol. The CTX reaction depended on effector cells bearing Tyl-1. Destruction of "innocent bystander" target cells was seen with one of four combinations of unfractionated and nonadherent peritoneal cells from hyperimmune animals.

Some immunological considerations relevant to the study of human bladder cancer.

The likelihood that immunosurveillance, concomitant immunity, and immunodepression play a role in the development and spread of neoplasms of the urinary bladder is discussed. The circumstantial evidence for the existence of concomitant immunity to bladder cancer-associated antigens is briefly reviewed, and the implications of the hypothesis of Zinkernagel and Dougherty of a genetic restriction to the cytotoxicity of T-cells for virally determined target cell antigens and of the concept of immunoregulatory cells for our understanding of the immunology of bladder carcinoma are discussed.

Decreased ability of blood leukocytes from patients with tumors of the urinary bladder to act as stimulator cells in mixed leukocyte culture.

Blood leukocytes from patients with active neoplasms of the urinary bladder were found to have a decreased ability to stimulate in one-way mixed leukocyte culture (MLC). The ability of the patients' leukocytes to act as stimulator cells in one-way MLC was assessed by simultaneous comparison to the ability of leukocytes from normal individuals to stimulate. In addition, the ability of the patients' leukocytes to act as responder cells in the one-way MLC was evaluated. Cells from 31 (56%) of 55 patients with active disease exhibited subnormal stimulatory activity in the MLC while 26 of these 31 patients (84%) had normal responsiveness. Cells from 9 of the 55 failed to respond normally. Poor stimulation occurred with both early and advanced disease, and the stimulatory activity increased after tumor removal in 12 of 15 patients who had previously shown subnormal stimulation. Six patients without active disease at the time of testing, in addition to the 55, exhibited normal levels of stimulation and responsiveness. This defective stimulatory activity is suggestive of an acquired, disease-related phenomenon and is not necessarily associated with decreased blood leukocyte responsiveness.

Detection of somatic mutations at the glycophorin A locus in erythrocytes of atomic bomb survivors using a single beam flow sorter.

A modified method was developed for measuring the frequency of variant erythrocytes at the glycophorin A locus using a single beam cell sorter (SBS). Fluorescein- or phycoerythrin-labeled monoclonal antibodies specific for the M or N glycophorin A alleles were used for the SBS assay. To prevent contamination of nucleated cells in the sorting windows, the nucleated cells in the fixed erythrocyte sample were stained with propidium iodide before flow sorting. Blood samples were obtained from atomic bomb survivors who were heterozygous for the MN blood type, and the frequencies of the hemizygous and homozygous variant of the M or N glycophorin A allele were measured by the SBS. For the three types of variants, hemizygotes for M and N allele (Nø and Mø) and homozygotes for M allele (MM), the variant frequency measured by the SBS correlated well with that previously determined by a dual beam cell sorter. Variant frequencies of the Nø, Mø, and MM cell types in atomic bomb survivors determined by SBS measurements were found to increase with radiation dose (DS86, kerma) as well as with the frequency of chromosome aberrations in lymphocytes.

A NEW SEMI-EMPIRICAL AMBIENT TO EFFECTIVE DOSE CONVERSION MODEL FOR THE PREDICTIVE CODE FOR AIRCREW RADIATION EXPOSURE (PCAIRE).

The Predictive Code for Aircrew Radiation Exposure (PCAIRE) is a semi-empirical code that estimates both ambient dose equivalent, based on years of on-board measurements, and effective dose to aircrew. Currently, PCAIRE estimates effective dose by converting the ambient dose equivalent to effective dose (E/H) using a model that is based on radiation transport calculations and on the radiation weighting factors recommended in International Commission on Radiological Protection (ICRP) 60. In this study, a new semi-empirical E/H model is proposed to replace the existing transport calculation models. The new model is based on flight data measured using a tissue-equivalent proportional counter (TEPC). The measured flight TEPC data are separated into a low- and a high-lineal-energy spectrum using an amplitude-weighted 137Cs TEPC spectrum. The high-lineal-energy spectrum is determined by subtracting the low-lineal-energy spectrum from the measured flight TEPC spectrum. With knowledge of E/H for the low- and high-lineal-energy spectra, the total E/H is estimated for a given flight altitude and geographic location. The semi-empirical E/H model also uses new radiation weighting factors to align the model with the most recent ICRP 103 recommendations. The ICRP 103-based semi-empirical effective dose model predicts that there is a ∼30 % reduction in dose in comparison with the ICRP 60-based model. Furthermore, the ambient dose equivalent is now a more conservative dose estimate for jet aircraft altitudes in the range of 7-13 km (FL230-430). This new semi-empirical E/H model is validated against E/H predicted from a Monte Carlo N-Particle transport code simulation of cosmic ray propagation through the Earth's atmosphere. Its implementation allows PCAIRE to provide an accurate semi-empirical estimate of the effective dose.

Inhibition of collagen synthesis with prolyl 4-hydroxylase inhibitor improves left ventricular function and alters the pattern of left ventricular dilatation after myocardial infarction.

Background- Left ventricular (LV) remodeling after myocardial infarction (MI) is associated with fibrosis, dilatation, and dysfunction. We postulated that prevention of fibrosis after MI with a prolyl 4-hydroxylase inhibitor (P4HI) would preserve LV function and attenuate LV enlargement. Methods and Results- Adult female rats (200 to 250 g) had experimental MI and were then randomized to treatment with P4HI (MI-FG041, n=29) or vehicle (MI-control, n=29) 48 hours after MI for 4 weeks in 2 phases. Echocardiograms were performed weekly with a 15-MHz linear transducer, and at 4 weeks, collagen isoform determinations and in vivo hemodynamics were performed. At randomization, the infarct size and LV function and size were similar in MI-FG041 and MI-control but significantly different from shams (n=9). At week 4, the LV function in MI-FG041 was significantly better than in MI-controls (fractional shortening 21% versus 16%, P=0.01; fractional area change 30% versus 19%, P=0.002; ejection fraction 35% versus 23%, P=0.001). In the FG041 group, LV area in systole was less (P<0.05), the dP/dt(max) after isoproterenol was higher (P<0.05), and types I and III collagen in noninfarcted LV were less than in MI-control. The hydroxyproline/proline ratio was increased by 64% in MI-control and reduced to the sham value in MI-FG041 rats. In the scar tissue, it was reduced by 24% in MI-FG041. Conclusions- This study demonstrates that prevention of interstitial fibrosis with a P4H inhibitor alters the pattern of LV enlargement and produces partial recovery of LV function after MI.

Automated radioxenon monitoring for the comprehensive nuclear-test-ban treaty in two distinctive locations: Ottawa and Tahiti.

In preparation for verification of the Comprehensive Nuclear-Test-Ban-Treaty, automated radioxenon monitoring is performed in two distinctive environments: Ottawa and Tahiti. These sites are monitored with SPALAX (Systeme de Prelevement d'air Automatique en Ligne avec l'Analyse des radioXenons) technology, which automatically extracts radioxenon from the atmosphere and measures the activity concentrations of (131m,133m,133,135)Xe. The resulting isotopic concentrations can be useful to discern nuclear explosions from nuclear industry xenon emissions. Ambient radon background, which may adversely impact analyser sensitivity, is discussed. Upper concentration limits are reported for the apparently radioxenon free Tahiti environment. Ottawa has a complex radioxenon background due to proximity to nuclear reactors and medical isotope facilities. Meteorological models suggest that, depending on the wind direction, the radioxenon detected in Ottawa can be characteristic of the normal radioxenon background in the Eastern United States, Europe, and Japan or distinctive due to medical isotope production.

Motivational interviewing targeting diet and physical activity improves adherence to paediatric obesity treatment: results from the MI†Values randomized controlled trial.

BACKGROUND: Adherence is a challenge in obesity treatment. Motivational interviewing (MI) may promote patient adherence. MI Values is a randomized controlled trial of MI implemented as an adjunct to an adolescent obesity treatment [Teaching Encouragement Exercise Nutrition Support (T.E.E.N.S.)]. OBJECTIVE: Assess effects of MI Values on T.E.E.N.S. attrition and adherence. METHODS: Participants were randomized to MI (n = 58) or control (n = 41). At weeks 1 and 10, MI participants had brief MI sessions; controls viewed health education videos. All participants continued with T.E.E.N.S. (biweekly dietitian and behavioural support visits; 3 times per week supervised physical activity). Assessments were repeated at baseline, 3 and 6 months. T-tests and chi-square analyses examined T.E.E.N.S. attrition and adherence by group. RESULTS: Adolescents (N = 99) were primarily African-American (73%) females (74%); age = 13.8 ± 1.8 years, body mass index percentile = 98.0 ± 1.2. Compared with controls, MI participants had greater 3-month adherence overall (89.2% vs. 81.0%, P = 0.040), and to dietitian (91.3% vs. 84.0%; P = 0.046) and behavioural support (92.9% vs. 85.2%; P = 0.041) visits, and greater 6-month adherence overall (84.4% vs. 76.2%, P = 0.026) and to behavioural support visits (87.5% vs. 78.8%, P = 0.011). CONCLUSIONS: MI enhanced adherence to this obesity intervention. MI Values is the first study to examine the impact of MI on treatment adherence among obese, primarily African-American adolescents.

Selective identification and differentiation of N- and O-linked oligosaccharides in glycoproteins by liquid chromatography-mass spectrometry.

A mass spectrometry method has been developed for selective detection of glycopeptides at the low (< or = 25) picomole level during chromatography of glycoprotein digests and for differentiation of O-linked from N-linked oligosaccharides. The technique involves observation of diagnostic sugar oxonium-ion fragments, particularly the HexNAc+ fragment at m/z 204, from collisionally excited glycopeptides. Collision-induced fragmentation can be accomplished in either of two regions of a triple quadrupole mass spectrometer equipped with an atmospheric pressure, electrospray (ES) ionization source. If collisions before the first quadrupole are chosen, it is possible to enhance formation of carbohydrate-related fragment ions without distorting the distribution of peptide and glycopeptide signals by increasing the collisional excitation potential only during that portion of each scan in which the low mass carbohydrate-related ions are being detected. This procedure, requiring only a single quadrupole instrument, identifies putative glycopeptide-containing fractions in the chromatogram but suffers from a lack of specificity in the case of co-eluting peptides. Increased specificity is obtained by selectively detecting only those parent ions that fragment in Q2, the second collision region of the triple quadrupole, to produce an ion at m/z 204 (HexNAc+). Only (M + H)+ ions of glycopeptides are observed in these liquid chromatography-electrospray tandem mass spectrometry (LC-ESMS/MS) "parent-scan" spectra. N-linked carbohydrates are differentiated from O-linked by LC-ESMS/MS analysis of the digested glycoprotein prior to and after selective removal of N-linked carbohydrates by peptide N:glycosidase F. These methods, which constitute the first liquid chromatography-mass spectrometry (LC-MS)-based strategies for selective identification of glycopeptides in complex mixtures, facilitate location and preparative fractionation of glycopeptides for further structural characterization. In addition, these techniques may be used to assess the compositional heterogeneity at specific attachment sites, and to define the sequence context of the attachment site in proteins of known sequence. The strategy is demonstrated for bovine fetuin, a 42-kDa glycoprotein containing three N-linked, and at least three O-linked carbohydrates. Over 90% of the fetuin protein sequence was also corroborated by these LC-ESMS studies.

The inophyllums, novel inhibitors of HIV-1 reverse transcriptase isolated from the Malaysian tree, Calophyllum inophyllum Linn.

As part of a search for novel inhibitors of HIV-1 reverse transcriptase, the acetone extract of the giant African snail, Achatina fulica, was shown to be active. Fractionation of the extract yielded inophyllums A, B, C, and E and calophyllolide (1a, 2a, 3a, 3b, and 6), previously isolated from Calophyllum inophyllum Linn., a known source of nutrition for A. fulica. From a methanol/methylene chloride extract of C. inophyllum, the same natural products in considerably greater yield were isolated in addition to a novel enantiomer of soulattrolide (4), inophyllum P (2b), and two other novel compounds, inophyllums G-1 (7) and G-2 (8). The absolute stereochemistry of inophyllum A (1a) was determined to be 10(R), 11(S), 12(S) from a single-crystal X-ray analysis of its 4-bromobenzoate derivative, and the relative stereochemistries of the other inophyllums isolated from C. inophyllum were established by a comparison of their 1H NMR NOE values and coupling constants to those of inophyllum A (1a). Inophyllums B and P (2a and 2b) inhibited HIV reverse transcriptase with IC50 values of 38 and 130 nM, respectively, and both were active against HIV-1 in cell culture (IC50 of 1.4 and 1.6 microM). Closely related inophyllums A, C, D, and E, including calophyllic acids, were significantly less active or totally inactive, indicating certain structural requirements in the chromanol ring. Altogether, 11 compounds of the inophyllum class were isolated from C. inophyllum and are described together with the SAR of these novel anti-HIV compounds.

Suppressed antidonor MLC responses in renal transplant candidates conditioned with donor-specific transfusions that carry the recipient's noninherited maternal HLA haplotype.

Forty-seven patients with end-stage renal disease were entered into a donor-specific transfusion protocol consisting of three infusions of whole blood every two weeks prior to transplantation. Fourteen of the patients became sensitized following transfusion and were not transplanted. Thirty-one patients received a transplant from the DST donor and have an estimated two-year graft survival of 97%, three-year survival of 88%, and four-year survival of 69%. Cells of eleven of the 36 recipients tested in one-way MLC before and two weeks after completion of DST exhibited a significantly decreased antidonor MLC response. Deletion of CD8+ positive lymphocytes from suppressed MLCs resulted in restoration of antidonor MLC reactivity in four of six patients. An analysis of the family HLA profile in patients exhibiting a decreased donor-directed MLC response revealed a significant (P less than 0.02) association between decreased MLC reactivity following DST and the expression of noninherited maternal HLA antigens by cells of the transfusion donor. These alterations in cellular immune responses noted in some patients following DST are consistent with the appearance of specific antidonor T suppressor cells as a result of donor-specific transfusion.

In vitro recall of proliferative and cytolytic responses to minor histocompatibility antigens by dendritic cell enriched canine peripheral blood mononuclear cells.

It is difficult in vitro to demonstrate existent in vivo sensitization of dogs and humans to minor histocompatibility antigens. Using conventional one-way mixed leukocyte culture, when sensitized blood cells are stimulated with MHC antigen-matched sibling PBMC bearing the minor histocompatibility antigens, there is usually no proliferative or cytotoxic response detected. We reported previously that 0 of 17 dogs sensitized by transfusion of dog leukocyte antigen-identical littermate blood had proliferative responses in mixed leukocyte culture when unfractionated sibling PBMC were used as stimulator cells. We reasoned that this result might be due to the inability of unfractionated PBMC to efficiently present minor histocompatibility antigens to the in vivo-primed T cells, a function thought best performed by dendritic cells. When we used a low buoyant density Percoll fraction of canine PBMC, shown previously to be enriched in dendritic cells, as stimulator cells, we were able to generate cytotoxic and/or proliferative responses in mixed leukocyte culture in all 5 dogs that had been sensitized to minor histocompatibility antigens by transfusions of dog leukocyte antigen-identical sibling littermate blood. By contrast, using unfractionated PBMC as stimulator cells, we found evidence of sensitization in only 1 of the 5 dogs. These data support the concept that the presentation of minor histocompatibility antigens, in contrast to major histocompatibility antigens, to the immune system may be restricted to a subpopulation of professional APC.