Quantification of ventricular stress in univentricular hearts during early childhood using age-independent zlog-NT-proBNP

BACKGROUND

Children with univentricular hearts (UVH) undergo up to three palliative surgical procedures to achieve complete circulatory separation (Fontan circulation). As a marker of cardiac wall stress, NT-proBNP is a promising tool to assess systemic ventricular load in these patients. However, different reference intervals (RI) apply to each stage, as NT-proBNP is highly age-dependent.

METHODS

Children undergoing systemic-to-pulmonary (SP) shunt placement (stage 1), bidirectional cavopulmonary shunt (BCPS, stage 2) or total cavopulmonary connection (TCPC, stage 3) between 2011 and 2021 with NT-proBNP measurement within 7 days before surgery were included. Furthermore, outpatients after TCPC with NT-proBNP measurement were enrolled. Biomarker levels were evaluated using its age-adjusted z-score ("zlog-NT-proBNP"; age-independent RI, -1.96 to +1.96), allowing comparison between different stages and revealing changes in systemic ventricular load independent of the marked physiological decline in RI with age.

RESULTS

Overall, 289 children (227 before, 62 after TCPC) met the eligibility criteria. Median time between blood sampling and surgery (SP shunt/BCPS/TCPC) was 2 [1-3] days and 3.2 [2.0-4.5] years after TCPC. Age-adjusted zlog-NT-proBNP levels were 3.47 [2.79-3.93] in children with native UVH (before SP shunt), 3.10 [1.89-3.58] at stage 1 (before BCPS), 1.08 [0.51-1.88] at stage 2 (before TCPC), and 1.09 [0.72-1.75] at stage 3 (after TCPC/Fontan completion). Consequently, BCPS revealed the strongest decrease (median - 2.02 logarithmized standard deviations, p < 0.001).

CONCLUSIONS

In children with UVH undergoing staged Fontan palliation, zlog-NT-proBNP is a highly promising tool for course assessment of systemic ventricular load, independent of the age-related decline in physiological NT-proBNP concentration.

Bioactive adrenomedullin (bio-ADM) is associated with endothelial dysfunction in infants and children with complex congenital heart disease undergoing open-heart surgery on cardiopulmonary bypass

OBJECTIVES

Children with congenital heart disease (CHD) undergoing cardiac surgery on cardiopulmonary bypass (CPB) are at risk for systemic inflammation leading to endothelial dysfunction associated with increased morbidity. Bioactive adrenomedullin (bio-ADM) is a peptide regulating vascular tone and endothelial permeability. The aim of this study was to evaluate the dynamics of plasma bio-ADM in this patient cohort and its role in capillary leak.

METHODS

Plasma samples from 73 pediatric CHD patients were collected for bio-ADM measurement at five different timepoints (TP) in the pre-, intra-, and post-operative period. The primary endpoint was a net increase in bio-ADM levels after surgery on CPB. Secondary endpoints included association of bio-ADM levels with clinical signs for endothelial dysfunction.

RESULTS

Bio-ADM levels increased after surgery on CPB from pre-operative median of 12 pg/mL (IQR [interquartile range] 12.0-14.8 pg/mL) to a maximum post-operative median of 48.8 pg/mL (IQR 34.5-69.6 pg/mL, p<0.001). Bio-ADM concentrations correlated positively with post-operative volume balance, (r=0.341; p=0.005), increased demand for vasoactive medication (duration: r=0.415; p<0.001; quantity: TP3: r=0.415, p<0.001; TP4: r=0.414, p<0.001), and hydrocortisone treatment for vasoplegia (bio-ADM median [IQR]:129.1 [55.4-139.2] pg/mL vs. 37.9 [25.2-64.6] pg/mL; p=0.034). Patients who required pleural effusion drainage revealed higher bio-ADM levels compared to those who did not (median [IQR]: 66.4 [55.4-90.9] pg/mL vs. 40.2 [28.2-57.0] pg/mL; p<0.001).

CONCLUSIONS

Bio-ADM is elevated in children after cardiac surgery and higher levels correlate with clinical signs of capillary leakage. The peptide should be considered as biomarker for endothelial dysfunction and as potential therapeutic target in this indication.

Influence of Shunt Type on Survival and Right Heart Function after the Norwood Procedure for Aortic Atresia

The study objective was to compare the results after Norwood procedure between modified Blalock-Taussig shunt (MBTS) and right ventricle-to-pulmonary artery conduit (RVPAC) according to Sano in patients with hypoplastic left heart syndrome (HLHS) and aortic atresia (AA). A total of 146 neonates with HLHS and AA who underwent the Norwood procedure at our institution between 2001 and 2020 were divided into 2 groups according to shunt type (MBTS or RVPAC). Survival after the Norwood procedure was compared between the groups. Longitudinal right ventricular and tricuspid valve function in each group were evaluated using cubic splines method. RVPAC was performed in 103 patients and MBTS in 43 according to surgeon preference. There were no differences in the 30-day mortality rates (16.5% vs 16.3%, P  = 0.973). Survival at 0.5, 1 and 3 years was 79.6%, 74.6%, and 68.9% in RVPAC and 66.8%, 64.3%, and 58.5% in MBTS (P  =  0.293). Among 23 patients undergoing tricuspid valve procedure, different mechanisms of tricuspid regurgitation were observed between the groups. Longitudinal analysis revealed greater prevalence of late right ventricular dysfunction in RVPAC patients. In 77 patients who completed Fontan procedure, the postoperative N-terminal pro B-type natriuretic peptide value was significantly higher in RVPAC vs MBTS (554 vs 276 ng/L, P  =  0.007). No survival advantage of RVPAC over MBTS was observed in neonates with HLHS and AA undergoing the Norwood procedure. Longitudinal analysis demonstrated a greater prevalence of right ventricular dysfunction and higher N-terminal pro B-type natriuretic peptide values during late follow-up in patients with RVPAC.

Predicting Major Adverse Cardiovascular Events in Children With Age-Adjusted NT-proBNP

BACKGROUND

N-terminal pro-B-type natriuretic peptide (NT-proBNP) is frequently used as a valuable prognostic biomarker in cardiac diseases. In children, however, it has not been established because of its strong age dependency. To overcome this obstacle, we recently introduced the zlog value of N-terminal pro-B-type natriuretic peptide (zlog-proBNP) as an age-adjusted reference.

OBJECTIVES

This study evaluates the prognostic power of zlog-proBNP for the occurrence of major adverse cardiovascular events (MACE) throughout childhood in patients with congenital heart diseases (CHD).

METHODS

A total of 910 children with CHD (median age 5 months; range 0.0-18.0 years) were included. MACE was defined as death, resuscitation, mechanical circulatory support, or hospitalization caused by cardiac decompensation. Because the physiological NT-proBNP concentration decreases significantly during childhood, zlog values were applied for an age-independent evaluation.

RESULTS

MACE occurred in 138 children during a median follow-up of 6 months (range 1 day to 7.6 years). High zlog-proBNP values (>+3.0) were most strongly associated with adverse events (n = 93; adjusted HR: 21.1; 95% CI: 2.9-154.2; P < 0.001). Among all evaluated indicators, zlog-proBNP was the best predictor for MACE (adjusted HR: 1.52; 95% CI: 1.31-1.76; P < 0.001) along with age and predictively superior to absolute NT-proBNP values. A cutoff value of +1.96 (age-independent upper limit of the physiological NT-proBNP concentration) achieved a negative predictive value of >96%.

CONCLUSIONS

Zlog-proBNP overcomes the strong age dependency of NT-proBNP and is a powerful prognostic marker for age-independent exclusion and prediction of MACE in children with CHD. We therefore expect zlog-proBNP to play a pivotal role in the future management of children with heart diseases.

Continuous, complete and comparable NT-proBNP reference ranges in healthy children

Background

NT-proBNP is one of the most important biomarkers for the diagnosis and risk assessment of heart failure in adults. Age- and gender-independent reference intervals (RIs) have been reported. In contrast, RIs in children are strongly age-dependent, do not exist for all ages and reveal a right-skewed distribution. Accordingly, no common Z-score can be formed and a cross-age interpretive method, so far, is missing.

Methods

Within the paper on hand, new evaluation techniques are applied to already published NT-proBNP study results and additionally to newly gained data. Upper limits (ULs), lower limits (LLs) and 50th percentiles are tested for power-like behavior as a function of age using linear regression analysis. Functions for continuous RIs are derived and reference limits are calculated on a per day basis. A corresponding Zlog formula is deduced and its usefulness is stated in two clinical examples.

Results

The power-like behavior of NT-proBNP concentration from birth to 18 years is demonstrated. With age in days t and measured NT-proBNP value x in pg/mL, an age-specific Zlog value may directly be calculated using the equation:

Zlog NT-proBNP = log   x + 0.512 ⋅ log   t − 3.417 1.489 + 0.014 ⋅ log   t ⋅ 3.92 ${\rm{Zlo}}{{\rm{g}}_{{\rm{NT - proBNP}}}} = {{\log \;x + 0.512 \cdot \log \;t - 3.417} \over {1.489 + 0.014 \cdot \log \;t}} \cdot 3.92$

Conclusions

Using formulas for UL and LL, continuous RIs from 0 to 18 years may be obtained. Continuity corresponds to physiological changes in the body much better than discrete RIs. With the advent of an NT-proBNP-specific Zlog value, a cross-age Z-score equivalent is providing an easy interpretation aid in everyday pediatric practice. This new approach allows to identify clinical worsening much better, sooner and more clearly than previous absolute values.

Assessment of efficacy and safety of the herbal medicinal product BNO 1016 in chronic rhinosinusitis

BACKGROUND

The objective of this clinical trial (CRS-02) was to assess the efficacy, safety and tolerability of two dosages of the herbal medicinal product BNO 1016 (Sinupret extract) in patients with chronic rhinosinusitis (CRS).

METHODOLOGY

929 patients suffering from CRS were enrolled in this randomised placebo-controlled trial with a treatment period of 12 weeks. The primary endpoint was the mean Major Symptom Score (MSS) in week 8 and week 12 compared to placebo. Secondary endpoints included further MSS related parameters and responder rates over time. Pharmacoeconomic endpoints were also analysed. Finally, safety and tolerability were evaluated.

RESULTS

Sinupret extract was not superior over placebo regarding the primary endpoint. However, the results of the secondary endpoints showed a clear trend towards superior efficacy. Therefore, additional post-hoc sensitivity analyses were performed in patients with a baseline MSS over 9 and persistence of disease more than 1 year diagnosed by specialists in otorhinolaryngology. Those patients significantly benefited from Sinupret extract. Therapy was superior for the primary endpoint analysis. Patients were less impaired with respect to work and daily activities. A good safety and tolerability of Sinupret extract was assured in all patients.

CONCLUSIONS

Sinupret extract can safely be administered in patients with CRS. Although the primary endpoint of the study was not significant, a post-hoc subgroup analysis in patients whose disease was diagnosed by a specialist revealed a pronounced treatment effect. Effects in that subgroup were even stronger with longer disease persistence and stronger severity.

Erbium Doped Silicon for Light Emitting Devices

We report on the excitation and de-excitation processes of erbium implanted in silicon and the integration of Si:Er light emitting devices (LED) with standard CMOS technology. We find two deexcitation processes, an Auger process below 100 K and a phonon mediated energy backtransfer above 100 K. We present the first optical voice link with a silicon LED as the emitter. Optical transmission system performance with our LED is possible below 200 K.

Where are We going? Overview of Major Collaborative Conservation Research Projects and Implications for the Future Preservation of Collections

In this paper I will tell you about some research and strategic projects, some of them at the end of their time and some just started. Although digitisation seems to have been a major topic in archives and libraries since the mid 1990s the vast majority of the collections are still based on traditional, i.e. analogue, media. The preservation problems much discussed prior to this still exist and still present some major hazards. What differs today from yesterday is that the technological progress has given us new means within reasonable costs to perform research and develop new tools as well as improve the monitoring of decay.

Exhaled NO and plasma cGMP increase after endotoxin infusion in healthy volunteers

Nitric oxide (NO) is believed to be involved in the pathophysiology of sepsis. This study evaluated the activity of the NO pathway in a human endotoxin model. At baseline and after endotoxin, on-line measurements of exhaled NO (eNO) were made using a chemiluminescence technique with a single-breath method. NO-free air was inhaled prior to exhalation against a resistance. NO in orally and nasally exhaled air and in rectal gas was investigated. Plasma nitrite, nitrate, and guanosine 3', 5'-monophosphate (cGMP) and the events after diclophenac administration were also studied. Endotoxin infusion resulted in tachycardia and fever. An early increase in oral eNO concentration was observed and oral eNO decreased after diclophenac administration. NO exhaled nasally, NO in rectum gas and nitrite/nitrate levels remained unchanged over the study period, cGMP increased after 4 h. These findings suggest an early increase in nitric oxide production from the lungs, probably due to increased activity of the constitutive nitric oxide synthase upon endotoxin stimulation. In contrast, nitric oxide production in the upper airways, measured as nasally exhaled nitric oxide and nitric oxide in rectal gas, remained unchanged. Further studies will elucidate if exhaled nitric oxide is a valuable marker of sepsis-induced lung injury and if monitoring of treatment is possible.

Nitric oxide but not carbon monoxide is continuously released in the human nasal airways

Results from different laboratories indicate that nitric oxide (NO) and carbon monoxide (CO) coexist in the human airways both in health and disease. These gases are present in exhaled human breath and high concentrations of NO as well as CO have been reported in the nasal airways. In addition, exhaled CO and NO are increased in patients with airways inflammation. NO and CO were measured simultaneously in orally exhaled air and in air sampled from the nose in 18 healthy subjects using chemiluminescence (for NO) and infrared (for CO) techniques at different fixed flow rates. The acute effects of smoking on airway release of NO and CO were also studied. Nasal NO was detected in all subjects and the concentrations were highly flow-dependent (mean+/-SEM: 236+/-23 and 527+/-49 parts per billion (ppb), at 2 and 0.5 L x min(-1), respectively). In contrast, no evidence of CO release in the nasal airways regardless of sample flow rate was found. In fact, additional experiments indicated a net absorption of CO when low levels of this gas were flushed through the nasal cavity. Nasal CO also remained undetectable after smoking. Both NO (22+/-2 ppb) and CO (1.1+/-0.1 parts per million) were consistently found in orally exhaled air. CO, but not NO, levels increased acutely after smoking a cigarette. The authors conclude that the patterns of nitric oxide and carbon monoxide release in the airways seem to differ profoundly in healthy subjects. Orally exhaled air contains both nitric oxide and carbon dioxide whereas nasal air contains nitric oxide only.

Nasal nitric oxide is reduced in patients with HIV

The gas nitric oxide (NO) is present in high concentrations in human nasal airways. Since NO is known to inhibit the growth of bacteria and viruses, it has been suggested that airborne NO represents the first line of defence against pathogens in the upper airways. Low nasal NO levels have been reported previously in patients susceptible to upper airway infection. Since HIV-positive patients are at risk for respiratory tract infections, including sinusitis, we studied the levels of NO in the upper and lower airways of these patients. A cross-sectional study with age-matched HIV patients and controls was carried out. Nasal and orally exhaled NO were measured in 31 HIV patients and 26 controls using a well-established chemiluminescence method developed for measurements of gaseous NO in the airways. Nasal NO was 21%, lower (p < 0.05, Student's t-test) in HIV patients than in controls, whereas orally exhaled NO did not differ between the two groups. We conclude that nasal NO is reduced in patients with HIV infection. The reduction in nasal NO may contribute to the decreased resistance to airway infections in these patients.

Effects of sustained-release oral phenylpropanolamine on the nasal mucosa of healthy subjects

Phenylpropanolamine (PPA) is widely used as a nasal decongestant administered orally in sustained release preparations and, in Sweden, the recommended dose nowadays is 50 mg twice daily for adults. The aim of this placebo-controlled, cross-over study was to determine the onset and duration of the decongestive effect of 50 and 100 mg PPA in 15 healthy subjects. All subjects arrived at the laboratory at 07.30 h. After an acclimatisation, the nasal mucosal baseline was established with rhinostereometry and the minimal cross-sectional area was measured using acoustic rhinometry. The systolic and diastolic blood pressures were also determined. Then all subjects were given their study drugs for the day and the measurements were repeated every hour for 8 h. This procedure was repeated for 3 days at 48 h intervals between the days. For purposes of comparison, the decongestive effect of oxymetazoline nasal spray was studied on a separate day. The decongestive effect of 100 mg PPA was similar to that of topical oxymetazoline. It develops after 1 h and lasts for approximately 6 h. The decongestive effect of oxymetazoline was significantly greater than that of 50 mg PPA and that of 100 mg PPA was significantly greater than that of 50 mg PPA using rhinostereometry, but not when using acoustic rhinometry. However, 50 mg PPA had no significant decongestive effect, compared with placebo, with rhinostereometry or acoustic rhinometry. In the first 3 h after administration of PPA, there was a dose-response increase in the systolic and diastolic blood pressures, which then returned to baseline. In conclusion, this study shows that PPA in double the recommended dose, i.e. 100 mg, has a significant decongestive effect on the nasal mucosa in healthy subjects. However, when the dose of PPA is increased the systolic and diastolic blood pressures also increase.

Adenoma of the papillae of Vater. Report of eleven cases

Eleven patients with a preoperative diagnosis of adenoma of the papillae of Vater were followed up during the fifteen-year period from 1984 till 1998 in the Oulu University Hospital. Seven patients were treated primarily by transduodenal excision without any recurrences so far. One of these seven patients was found to have adenocarcinoma in a histological examination. Active surgery for adenoma of the papillae of Vater is recommended because of the precancerous nature of the lesion, and because malignancy cannot always be detected by endoscopic biopsies. Transduodenal excision could be recommend for patients at high operative risk, especially in cases with small adenomas and low-grade dysplasia, where histologically free resection margins can be achieved, but pancreaticoduodenectomy should still be performed on patients at low operative risk.

The value of herniography in the diagnosis of unexplained groin pain

Herniographies were performed on 106 outpatients with obscure groin pain. A total of 39 hernias were found in 38 patients (36%) and the 46 patients either operated on (40 patients) or who had undergone laparoscopy (six patients), included one false positive and two false negative ones. All three cases were inpatients who had earlier undergone surgery for inguinal hernia 27% of the patients with a normal clinical finding (19/70), 67% of those with previous inguinal herniotomy (8/12) and 50% of those with symptoms suggestive of hernia (12/24) had diagnostic findings on herniography. Thirteen out of the 48 women (27%) and 25 of the 58 men (43%) had positive finding at herniography. The valve of herniography was that 56 patients were spared subsequent surgical exploration because of normal herniographic finding. Our results indicate that herniography is a useful tool for the examination of patients with unexplained groin pain.

A structure-activity study of four dopamine D-1 and D-2 receptor antagonists, representing the phenylindan, -indene, and -indole structural classes of compounds

Representatives of the phenylindan, -indene, and -indole classes of compounds (3-6) have been tested for affinity for the dopamine D-1 and D-2 receptors. The compounds all display high affinities for these receptors. Conformational analysis using MM2(87) and subsequent molecular least-squares superimpositions have been performed in order to determine if the affinities of the compounds can be rationalized by a recently proposed dopamine D-2 receptor-interaction model. In spite of the different geometric and conformational properties, the compounds can be well accommodated into the model in their calculated lowest energy conformations. The molecular superimpositions allow the absolute configurations of the active enantiomers of 4 and 5 to be predicted. The present structure-activity study extends the receptor-interaction model by suggesting that the receptor is not very sensitive to the orientation of the p-fluorophenyl ring in 1 and 3-6 or to the exact spatial location of the associated fluoro substituent.

A study on the contribution of the 1-phenyl substituent to the molecular electrostatic potentials of some benzazepines in relation to selective dopamine D-1 receptor activity

The molecular electrostatic potentials for a selective dopamine D-1 receptor antagonist, 7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-methylbenzazepine (SCH 23390 (1], and a selective dopamine D-1 receptor agonist, 7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SK&F 38393 (2], have been calculated in order to obtain an understanding of the nature of the interactions between the phenyl ring and the receptor. Analogues of 1 with conformationally constrained phenyl rings have also been studied. Based on this study, the conclusion is drawn that an important part of the interaction between the phenyl ring in the benzazepines and the receptor is due to electrostatic forces, and that the phenyl ring interacts with the same receptor site as the oxygen atom of the 8-hydroxy group.

Reactivity of rat placental cells with alloantisera

The nature of the protection afforded the placental structure against the immunologic consequences that could result from maternal exposure to paternal alloantigens remains obscure. One problem has been difficulty in antigenically defining the individual cellular components of the intact placenta. These studies were designed to examine serologically, with specific antisera, five cell types isolated from the rat placenta. The results indicate that non-Ag-B antigens are present on the cytotrophoblast cells, while Ag-G antigens are absent on all the cells except an undefined population of fibroblasts. Of particular significance is the obvious absence of detectable surface antigens on the cells directly in contact with the maternal tissues, the trophoblast mononuclear giant cells.

Fuzzy, a hypotrichotic mutant in linkage group I of the Norway rat

A new recessive hypotrichosis gene in the rat designated fuzzy (fz) is described. Fuzzy is linked to albino (c) in linkage group I with a 18.13 +/- 3.05 percent recombination. After an initial sparse hair coat, the fuzzy animals rapidly become devoid of hair. Histologically the skin of these animals has poorly developed, and often cystic hair follicles that contain accumulations of keratinacious material.

Histologic characteristics of cells cultured from rat placental tissue

Laboratory animals, especially rats, have provided a comparative model for extensive research on maternal-fetal relationships. To identify individual placental cells for subsequent immunologic analysis, cultures of rat placentas were studied. Five cell types were observed, including: two histologically distinct giant cells, mononucleate and multinucleate, apparently formed by amitosis and fusion, respectively; small round cells; polygonal cells, probably cytotrophoblasts. Of particular interest are the small round cells which are phagocytic and morphologically similar to macrophages, cells known to be important in the immune response.

Genetic control of susceptibility to experimental allergic encephalomyelitis and the Ag-B locus of rats

Injection of guinea pig spinal cord with complete Freund's adjuvant induces EAE in Lewis (Ag-B1) and DA (Ag-B4) rats, but not in rats of the BN (Ag-B3) strain. When BN is crossed with Lewis, susceptibility is determined by a gene linked to the Ag-B histocompatibility locus, but a much more complex mode of inheritance is involved when BN and DA rats are crossed. Six inbred strains possessing the Ag-B1 histocompatibility allele have been found to be susceptible to EAE. Evidence for recombination between the Ag-B locus and the gene determining susceptibility to EAE has not yet been obtained.

Genetic control of susceptibility to experimental allergic encephalomyelitis in rats

Rats of the inbred strains Lewis and DA are highly susceptible to the induction of experimental allergic encephalomyelitis (EAE) while Brown Norway rats are resistant to this disease. Evidence has been obtained which suggests that a single dominant gene is associated with susceptibility to EAE. The locus controlling EAE susceptibility is closely linked to the Ag-B histocompatibility locus but is not identical to it.

Differential immunofluorescence of fertilized mouse eggs with H-2 and non-H-2 antibody

Mouse embryos at the two-cell and blastocyst stages, as well as unfertilized eggs, have been studied by indirect immunofluorescence for the expression of H-2 and non-H-2 histocompatibility antigens on surface membranes. Serologically-specific reactivity to non-H-2 antibody (H-3 and H-6) was observed as diffuse, patchy staining over the entire surface of the blastomeres at the two-cell stage. In contrast, no reactivity of two-cell or unfertilized egg embryos of four inbred strains was observed when antisera containing only multispecific H-2 cytolytic antibody were used. Antisera containing H-2 along with non-H-2 antibody of unknown specificity showed varying degrees of reactivity, which could be shown by absorption studies to be due to the non-H-2 content of the serum. The results suggest that the initial expression of histocompatibility genes varies and support the hypothesis that the appearance of these cell components may relate to specific stages of differentiation.

Gene control of hematopoiesis. I. Erythrocyte mosaicism and permanent immunological tolerance in allophenic mice

Erythropoietic cells of two unrelated strains, C3H (or C3Hf) and C57BL/6, can coexist throughout hematopoiesis in allophenic mice experimentally produced from aggregated, undifferentiated blastomeres of separate genotypes. The presence of two red cell genotypes in these circumstances signifies that the erythroid population must normally be multiclonal, i.e., derived mitotically from at least two genetically determined cells. The two strains were detected by hemagglutination and absorption tests of erythrocytes for the specific histocompatibility antigens dictated by the H-2(k) and H-2(b) alleles. Of 34 C3H(f) <--> C57BL/6 allophenics tested, 16 had both red cell types; the remaining 18 showed only C3H or C57 red cells and included 12 mice with both cell strains present in some other tissues. All animals with evidence of two H-2 phenotypes among circulating erythrocytes were permanently immunologically tolerant of both antigenic types and remained free of runt disease. They lived a full lifespan, up to 2 yr 7(1/2) months of age. The data suggest a possible specific selective advantage of C57BL/6 over C3H erythropoietic tissue. There is considerable individual variability, not only in proportions of antigenically distinct erythrocytes, but also in strain composition of other tissues in the same animals. A broad spectrum of distinctive situations is found, in which parameters are varied within or outside of the circulatory system. Allophenic mice can therefore serve as investigative tools for entirely new kinds of experimental studies of gene control mechanisms and blood physiology in normal hematopoiesis and in a number of hereditary blood diseases.