Kinetics of ectromelia virus (mousepox) transmission and clinical response in C57BL/6j, BALB/cByj and AKR/J inbred mice

Research was undertaken to answer basic questions on susceptibility, clinical response and transmission of ectromelia virus in selected strains of inbred mice. C57BL/6J and AKR/J were found to be markedly more resistant to a virulent strain of ectromelia virus (isolated during the 1979-80 outbreak at the National Institutes of Health) than C57LJ, BALB/cByJ, DBA/2J, A.By/SNJ and C3H/HeJ when infected by footpad inoculation. In C57BL/6J and AKR/J the LD50 was about 7 logs higher than the ID50. With one exception, C57LJ, the LD50 and ID50 titers in the other strains were about equal. In C57LJ the LD50 titer was intermediate. Following intragastric inoculation, virus was isolated from feces of C57BL/6J mice for as long as 46 days and up to 29 days from BALB/cByJ mice. Transmission to cage mates from intragastrically infected C57BL/6J and BALB/cByJ occurred up to 36 and 30 days respectively after infection. Virus was isolated from the spleen in 2 of 5 BALB/cByJ mice and 1 of 7 C57BL/6J mice tested 95 days after gastric inoculation. Following footpad inoculation, BALB/cByJ mice consistently transmitted virus to cage mates before death at 10-12 days. C57BL/6J mice transmitted between days 8 and 17, but not beyond. Virus was maintained in C57BL/6J mice by exposure to infected cage mates for seven passages, which was the most attempted. Clinical signs in infected C57BL/6J mice were usually subtle or inapparent.     

Resistance/susceptibility to lethal Sendai virus infection genetically linked to a mucociliary transport polymorphism.

Linkage was tested between a mucociliary transport polymorphism and resistance/susceptibility to lethal Sendai virus infection in segregant hybrid mice of C57BL/6J and DBA/2J parents. The distribution of paired phenotypes for tracheal mucociliary transport rates and susceptibility to lethal Sendai virus infection in 171 F1 X DBA/2J mice showed strong interaction of the parental phenotypes.     

Alteration of viral respiratory infections of mice by prior infection with mouse hepatitis virus

Pre-infection with mouse hepatitis virus (MHV) strains S, 3, or JHM reduced the ability of mice to seroconvert to PVM. Geometric mean antibody titers to PVM among MHV pre-infected mice were lower than those for control mice given only PVM, and dually infected mice seroconverted to PVM later than mice given PVM alone. PVM was not recovered from normally permissive respiratory tract tissues of MHV-S pre-infected mice. Pre-infection of DBA/2 mice with MHV-S compromised the susceptibility of these mice to lethal Sendai virus infection but did not substantially reduce the titers of infectious Sendai virus recovered from the lungs. Serologic responses to Sendai virus and lung Sendai virus titers were similar in Sendai virus-resistant C57BL/6 mice pre-infected or not with MHV-S.     

Differential antigen burden modulates the gamma interferon but not the immunoglobulin response in mice that vary in susceptibility to Sendai virus pneumonia.

Sendai virus, a paramyxovirus which causes murine pneumonia, grew to approximately 10-fold higher titers and was cleared less rapidly from the lungs of 129/J (129) than H-2b-compatible C57BL/6J (B6) mice. The more susceptible 129 mice also made higher titers of gamma interferon (IFN-gamma) and immunoglobulin G2a (IgG2a) virus-specific antibody. Analysis with acutely irradiated (950 rads) mice and immunologically reconstituted bone marrow (BM) radiation chimeras indicated that the enhanced virus growth was a function of the radiation-resistant respiratory epithelium. Prolonged exposure to more virus in turn influenced the magnitude of IFN-gamma production, most of which was made by CD4+ T lymphocytes. Somewhat surprisingly, however, the 129 pattern of a higher virus-specific serum Ig response skewed towards IgG2a mapped to the reconstituting BM. Thus, the characteristics of the humoral response are at least partly dissociated from both the antigen load, resulting from viral replication, and the level of IFN-gamma production. Further analysis of double chimeras (B6+129 BM-->B6 recipients) confirmed that the divergent humoral immune response to Sendai virus in B6 and 129 mice is largely determined by the inherent characteristics of the lymphoid cells.     

Effects of maternal strain on ethanol responses in reciprocal F1 C57BL/6J and DBA/2J hybrid mice

Variations in maternal behavior, either occurring naturally or in response to experimental manipulations, have been shown to exert long-lasting consequences on offspring behavior and physiology. Despite previous research examining the effects of developmental manipulations on drug-related phenotypes, few studies have specifically investigated the influence of strain-based differences in maternal behavior on drug responses in mice. The current experiments used reciprocal F1 hybrids of two inbred mouse strains (i.e. DBA/2J and C57BL/6J) that differ in both ethanol (EtOH) responses and maternal behavior to assess the effects of maternal environment on EtOH-related phenotypes. Male and female DBA/2J and C57BL/6J mice and their reciprocal F1 hybrids reared by either DBA/2J or C57BL/6J dams were tested in adulthood for EtOH intake (choice, forced), EtOH-induced hypothermia, EtOH-induced activity and EtOH-induced conditioned place preference (CPP). C57BL/6J and DBA/2J mice showed differences on all EtOH responses. Consistent with previous reports that maternal strain can influence EtOH intake, F1 hybrids reared by C57BL/6J dams consumed more EtOH during forced exposure than did F1 hybrids reared by DBA/2J dams. Maternal strain also influenced EtOH-induced hypothermic responses in F1 hybrids, producing differences in hybrid mice that paralleled those of the inbred strains. In contrast, maternal strain did not influence EtOH-induced activity or CPP in hybrid mice. The current findings indicate that maternal environment may contribute to variance in EtOH-induced hypothermia and EtOH intake, although effects on EtOH intake appear to be dependent upon the type of EtOH exposure.     

Latent inhibition and extinction of passive avoidance in mice C57BL/6J AND DBA/2J

The study was carried out in mice C57BL/6J and DBA/2J for comparative analysis of two interference processes: latent inhibition and extinction of passive avoidance produced with an unconditioned aversive stimulus of different parameters (0.5 and 0.25 mA). With a strong training to new stimulus, impairment of extinction has been detected only in mice DBA/2J. Reduction in the strength of punishment during training was accompanied by acceleration of extinction in mice C57BL/6J and its appearance in mice DBA/2J. The learning of passive avoidance in strong and weak reinforcement was the same for both strains of mice. Interline differences were found also in the analysis of latent inhibition. With strong and weak training to conditional stimulus, lost of novelty by repeated an 8-fold pre-exposures to the experimental chamber, in DBA/2J mice, in contrast to C57BL/6J, latent inhibition was disrupted. In addition, DBA/2J mice showed impairment of extinction with weak training to non-relevant stimulus.     

Streptobacillus moniliformis epizootic in barrier-maintained C57BL/6J mice and susceptibility to infection of different strains of mice

We report a Streptobacillus moniliformis epizootic in barrier-maintained SPF mice. Although various inbred and F1 hybrid strains of mice have been kept in this animal facility, only C57BL/6J Han [corrected] mice showed clinical signs of disease. During the course of the epizootic, 825 breeding animals (approximately 36% of the breeders) died or had to be killed because of severe clinical signs. Although sequential treatment with ampicillin and chlortetracycline gave good therapeutic results, the animal facility was vacated in order to exclude any risk of cross-contamination of the other rodent colonies in our institute. The source and route of transmission of S. moniliformis could not be elucidated. To investigate strain dependent differences experimental infection of different strains of mice with our S. moniliformis isolate was performed. After oral infection only C57BL/6J showed the typical signs of a cervical lymphadenitis and gave an immunological response. BALB/cJ, C3H/He, DBA/2J, CB6F1 and B6D2F1 mice were not affected except in two cases of DBA/2J and B6D2F1 mice where seroconversion was observed. After intravenous infection of C57BL/6J, DBA/2J [corrected] and BALB/cJ all animals showed positive titers in the indirect immunofluorescence test (IIF). One hundred percent of the C57BL/6J, forty percent of the DBA/2J, and none of the BALB/cJ mice developed severe symptoms. The results demonstrate that the susceptibility to streptobacillosis is predominantly influenced by genetic factors.     

Differential expression and regulation of myristoylated alanine-rich C kinase substrate (MARCKS) in the hippocampus of C57/BL6J and DBA/2J mice

The myristoylated alanine-rich C kinase substrate (MARCKS) is a major protein kinase C (PKC) substrate in brain that binds the inner surface of the plasma membrane, calmodulin, and cross-links filamentous actin, all in a PKC phosphorylation-reversible manner. MARCKS has been implicated in hippocampal-dependent learning and long-term potentiation (LTP). Previous studies have shown DBA/2 mice to exhibit poor spatial/contextual learning, impaired hippocampal LTP, and hippocampal mossy fiber hypoplasia, as well as reduced hippocampal PKC activity and expression relative to C57BL/6 mice. In the present study, we assessed the expression (mRNA and protein) and subcellular distribution (membrane and cytolsol) of MARCKS in the hippocampus and frontal cortex of C57BL/6 and DBA/2 mice using quantitative western blotting. In the hippocampus, total MARCKS mRNA and protein levels in C57BL/6J mice were significantly lower ( approximately 45%) compared with DBA/2J mice, and MARCKS protein was observed predominantly in the cytosolic fraction. MARCKS expression in frontal cortex did not differ significantly between strains. To examine the dynamic regulation of MARCKS subcellular distribution, mice from each strain were subjected to 60 min restraint stress and MARCKS subcellular distribution was determined 24 h later. Restraint stress resulted in a significant reduction in membrane MARCKS expression in C57BL/6J hippocampus but not in the DBA/2J hippocampus despite similar stress-induced increases in serum corticosterone. Restraint stress did not affect cytosolic or total MARCKS levels in either strain. Similarly, restraint stress (30 min) in rats also induced a significant reduction in membrane MARCKS, but not total or cytosolic MARCKS, in the hippocampus but not in frontal cortex. In rats, chronic lithium treatment prior to stress exposure reduced hippocampal MARCKS expression but did not affect the stress-induced reduction in membrane MARCKS. Collectively these data demonstrate higher resting levels of MARCKS in the hippocampus of DBA/2J mice compared to C57BL/6J mice, and that acute stress leads to a long-term reduction in membrane MARCKS expression in C57BL/6J mice and rats but not in DBA/2J mice. These strain differences in hippocampal MARCKS expression and subcellular translocation following stress may contribute to the differences in behaviors requiring hippocampal plasticity observed between these strains.     

Distinctive and critical roles for cellular immunity and immune-inflammatory response in the immunopathology of Sendai virus infection in mice

Respiratory viral infections result in severe pulmonary injury, to which host immune response may be a significant contributor. At present, it is not entirely clear the extent to which lung injury is a necessary consequence of host defense. In this report, we use functional genomics approach to characterize the key roles of cellular immunity and immune-inflammatory response in the immunopathology of Sendai virus infection in resistant C57BL/6J and susceptible DBA/2J mice. Infected mice manifested an immune-inflammatory response characterized by the pulmonary influx of neutrophils and mononuclear cells. DBA/2J mice mounted a vigorous immune response, with significant up-regulation of cytokine/chemokine genes in two successive waves through the course of infection. Whereas, C57BL/6J mice displayed an efficient immune response with less severe pathology and clusters of immune-inflammatory responsive genes were exclusively up-regulated on day 4 in this strain. Overall, DBA/2J mice exhibited a dysregulated hyper-inflammatory cytokine/chemokine cascades that does not limit viral spread resulting in a predisposition to severe lung pathology. This response is similar to severe human respiratory paramyxovirus infections, which will serve as a model for the elucidation of hyper-immune inflammatory response that result to severe immunopathology in respiratory viral infections.     

Genetic determinants of resistance to ectromelia (mousepox) virus-induced mortality.

Resistance to ectromelia (mousepox) virus-induced mortality was examined in crosses between susceptible DBA/2J, A/J, and BALB/cByJ mice and resistant C57BL/6J and AKR/J mice. Depending on the cross, resistance to mousepox virus was shown to be determined by one or more independently assorting autosomal loci with dominant alleles for resistance in AKR/J and C57BL/6J mice and recessive alleles in A/J, BALB/cByJ, and DBA/2J mice. A sexual dimorphism in resistance to disease was also observed.     

Abnormal metal levels in the primary visual pathway of the DBA/2J mouse model of glaucoma

The purpose of this study was to determine metal ion levels in central visual system structures of the DBA/2J mouse model of glaucoma. We used inductively coupled plasma mass spectrometry (ICP-MS) to measure levels of iron (Fe), copper (Cu), zinc (Zn), magnesium (Mg), manganese (Mn), and calcium (Ca) in the retina and retinal projection of 5-month (pre-glaucomatous) and 10-month (glaucomatous) old DBA/2J mice and age-matched C57BL/6J controls. We used microbeam X-ray fluorescence (μ-XRF) spectrometry to determine the spatial distribution of Fe, Zn, and Cu in the superior colliculus (SC), which is the major retinal target in rodents and one of the earliest sites of pathology in the DBA/2J mouse. Our ICP-MS experiments showed that glaucomatous DBA/2J had lower retinal Fe concentrations than pre-glaucomatous DBA/2J and age-matched C57BL/6J mice. Pre-glaucomatous DBA/2J retina had greater Mg, Ca, and Zn concentrations than glaucomatous DBA/2J and greater Mg and Ca than age-matched controls. Retinal Mn levels were significantly deficient in glaucomatous DBA/2J mice compared to aged-matched C57BL/6J and pre-glaucomatous DBA/2J mice. Regardless of age, the SC of C57BL/6J mice contained greater Fe, Mg, Mn, and Zn concentrations than the SC of DBA/2J mice. Greater Fe concentrations were measured by μ-XRF in both the superficial and deep SC of C57BL/6J mice than in DBA/2J mice. For the first time, we show direct measurement of metal concentrations in central visual system structures affected in glaucoma and present evidence for strain-related differences in metal content that may be specific to glaucomatous pathology.     

The genetics of aryl hydrocarbon hydroxylase induction in mice: A single gene difference between C57BL/6J and DBA/2J

Twenty-one inbred strains of mice were surveyed for inducibility of hepatic aryl hydrocarbon hydroxylase (AHH) activity by the carcinogen 3-methylcholanthrene (MC). In 11 strains given MC, AHH activity increased 1.3- to 5-fold (inducible), whereas ten strains responded with a less than 0.5-fold increase (noninducible). Neither the inducible nor the noninducible class was homogeneous, and in each considerable variation was found in both the basal activity of AHH and the response to MC. Strains DBA/2J and C57BL/6J were chosen to represent the noninducible and inducible classes, respectively. In the crosses (C57BL/6 × DBA/2)F₁ × DBA/2 and (C57BL/6 × DBA/2)F₂, inducibility segregated as a single autosomal dominant gene. The gene symbols Ahh ⁱ and Ahh ⁿ are proposed for the alleles present in C57BL/6J and DBA/2J, respectively. No genetic linkage was found between the Ahh locus and the following loci: b, d, Es-1, Es-3, Gpd-1, Hbb, Id-1, Pgm-1, and sex. Some implications of this work in the study of mammalian enzyme induction and chemically induced carcinogenesis are discussed. There is a positive correlation between AHH inducibility and the development of an inflammatory response to the topical application of the carcinogen 7,12-dimethylbenzanthracene.     

Gene expression of the repulsive guidance molecules/neogenin in the developing and mature mouse visual system: C57BL/6J vs. the glaucoma model DBA/2J

We used in-situ hybridization to analyze the expression patterns of three known members (a, b and c) of the RGM (“repulsive guidance molecule”) gene family and of the RGMa receptor neogenin in a glaucoma mouse model (DBA/2J strain) and the C57BL/6J strain, which served as a control. In order to understand the role of the RGMs and neogenin in glaucoma, we characterized their expression patterns in the developing and mature mouse retina and in the optic nerve. In all investigated stages from post-natal day (P) 0 to 15 months (M) RGMa, RGMb and neogenin expression was detected in the ganglion cell layer (GCL). From P10 to 15 M, we found RGMa, RGMb and neogenin expression in the inner nuclear layer (INL) and the outer nuclear layer (ONL). In P10- and older mice, the expression patterns of RGMa and its receptor neogenin were similar, while that of RGMb differed from both. As expected, no specific retinal expression of RGMc was detected in any of the age groups investigated. C57BL/6J mice and DBA/2J mice displayed no differences in the expression pattern of RGMa, RGMb, RGMc and neogenin in the developing retina (gestational age 14.5 days (E14.5), P0 & P10). Interestingly, we found a higher expression of RGMa, RGMb and neogenin in the retinas of all glaucoma-affected mice than in the age-matched control strain. Furthermore, we detected a higher RGMa and RGMb expression in the optic nerves of glaucoma-affected DBA/2J-mice older than 11 M than in C57BL/6J mice of the same age.     

Genetic and phenotypic analysis of seizure susceptibility in PL/J mice

Epilepsy is one of the most common but genetically complex neurological disorders in humans. Identifying animal models that recapitulate human epilepsies is important for pharmacological studies of anticonvulsants, dissection of molecular and biochemical pathogenesis of epilepsy, and discovery of epilepsy susceptibility genes. We discovered that the PL/J inbred mouse strain is susceptible to handling- and rhythmic tossing–induced seizure. The tonic–clonic and generalized seizures observed after induction were accompanied by abnormal EEGs, similar to seizures observed in EL and SWXL-4 mice. PL/J mice also had an extremely low threshold to electroconvulsive seizures compared to other strains and showed variable sensitivity to pentylenetetrazole-induced seizures. Gross neurostructural abnormalities were not found in PL/J mice. Crosses with the seizure-resistant C57BL/6 J strain revealed semidominant inheritance of the rhythmic tossing seizure trait with low penetrance. F2 progeny indicated that the genetic inheritance of seizure susceptibility in PL/J is non-Mendelian. We crossed DBA/2 J mice, which are resistant to rhythmic tossing seizure but susceptible to audiogenic seizures, to PL/J. We found that seizure penetrance in (DBA/2 J × PL/J)F1 mice was similar to the penetrance in (C57BL/6 J × PL/J)F1 mice but the severity and frequency of seizure were higher in (DBA/2 J × PL/J)F1 mice. The PL/J strain serves as an interesting new model for studying the genetics, neurobiology, and pharmacology of epilepsy.     

Genetic control of sex-chromosomal univalency in the spermatocytes of C57BL/6J and DBA/2J mice

The genetic control of sex-chromosomal univalency was examined in the primary spermatocytes of the mouse. The C57BL/6J strain expresses 3% X-Y univalency and DBA/2J expresses 37% univalency. The reciprocal F1 and the eight types of reciprocal backcross males were examined. In the C57BL/6J--DBA/2J strain pair, X--Y univalency is controlled by three genetic systems. Autosomal factors of unknown number that are dominant in DBA/2J increase the probability of univalency from 3% in C57BL/6J to 12%. The DBA/2J-Y chromosome, in place of the C57BL/6J-Y chromosome, has an additive effect to increase the probability of univalency from 12 to 37% in the DBA/2J strain. Two X-chromosome factors that differ between C57BL/6J and DBA/2J regulate the probability of univalency. The X-chromosome factors appear to be separated by sufficient distance so that, with the DBA/2J-Y chromosome and dominant DBA/2J autosomal factors, there are two recombinant classes of X--Y univalency at 20 and 60%. The genetic factors in the univalency trait may be involved in the regulation or structure of the terminal attachment sites between the X and Y chromosomes.     

Effects of an early handling-like procedure and individual housing on anxiety-like behavior in adult C57BL/6J and DBA/2J mice

Manipulations of rearing conditions have been used to examine the effects of early experience on adult behavior with varying results. Evidence suggests that postnatal days (PND) 15-21 are a time of particular susceptibility to environmental influences on anxiety-like behavior in mice. To examine this, we subjected C57BL/6J and DBA/2J mice to an early handling-like procedure. Pups were separated from dams from PND 12-20 for 30 minutes daily or received standard care. On PND 21, pups were weaned and either individually- or group-housed. On PND 60, anxiety-like behavior was examined on the elevated zero-maze. Although individually-housed animals took longer to enter an open quadrant of the maze, they spent more time in the open than group-housed animals. Additionally, we observed a trend of reduced anxiety-like behavior in C57BL/6J, but not DBA/2J mice that underwent the handling-like procedure.     

Epstein-Barr virus nuclear antigen 1 does not cause lymphoma in C57BL/6J mice

To test whether transgenic Epstein-Barr virus nuclear antigen 1 (EBNA1) expression in C57BL/6 mouse lymphocytes causes lymphoma, EBNA1 expressed in three FVB lineages at two or three times the level of latent infection was crossed up to six successive times into C57BL/6J mice. After five or six crosses, 14/36, (38%) EBNA1 transgenic mice, 11/31 (36%) littermate EBNA1-negative controls, and 9/25 (36%) inbred C57BL/6J mice housed in the same facility had lymphoma. These data indicate that EBNA1 does not significantly increase lymphoma prevalence in C57BL/6J mice.     

Gene expression of the repulsive guidance molecules/neogenin in the developing and mature mouse visual system: C57BL/6J vs. the glaucoma model DBA/2J

We used in-situ hybridization to analyze the expression patterns of three known members (a, b and c) of the RGM ("repulsive guidance molecule") gene family and of the RGMa receptor neogenin in a glaucoma mouse model (DBA/2J strain) and the C57BL/6J strain, which served as a control. In order to understand the role of the RGMs and neogenin in glaucoma, we characterized their expression patterns in the developing and mature mouse retina and in the optic nerve. In all investigated stages from post-natal day (P) 0 to 15 months (M) RGMa, RGMb and neogenin expression was detected in the ganglion cell layer (GCL). From P10 to 15M, we found RGMa, RGMb and neogenin expression in the inner nuclear layer (INL) and the outer nuclear layer (ONL). In P10- and older mice, the expression patterns of RGMa and its receptor neogenin were similar, while that of RGMb differed from both. As expected, no specific retinal expression of RGMc was detected in any of the age groups investigated. C57BL/6J mice and DBA/2J mice displayed no differences in the expression pattern of RGMa, RGMb, RGMc and neogenin in the developing retina (gestational age 14.5 days (E14.5), P0 & P10). Interestingly, we found a higher expression of RGMa, RGMb and neogenin in the retinas of all glaucoma-affected mice than in the age-matched control strain. Furthermore, we detected a higher RGMa and RGMb expression in the optic nerves of glaucoma-affected DBA/2J-mice older than 11M than in C57BL/6J mice of the same age.     

GABA(A) receptor beta(2) subunit mRNA content is differentially regulated in ethanol-dependent DBA/2J and C57BL/6J mice

Chronic ethanol treatment is known to alter gene expression and function of γ-aminobutyric acid type-A (GABA_A) receptors. Here we focus on the β₂ subunit which is widely expressed in the mammalian brain, and plays a key role in the GABA binding site. Previous studies using rodent models of ethanol dependence show either increased or no change of β₂ subunit mRNA and peptide content following chronic ethanol administration. In humans, polymorphism at the β₂ subunit is associated with ethanol dependence in some, but not all, populations. In the present study we measured mRNA content in the cerebellum and cerebral cortex using ethanol-naive and ethanol-dependent DBA/2J and C57BL/6J mice. The DBA/2J strain displays severe ethanol withdrawal severity, while the C57BL/6J strain shows milder withdrawal reactions. RNase protection analysis demonstrated that the DBA/2J strain is more sensitive to ethanol-induced increases in β₂ subunit mRNA content in the cerebellum, showing significant increases at lower blood ethanol concentrations than C57BL/6J mice. The ethanol-induced regulation in C57BL/6J mice appears to be more complex, with decreases in β₂ subunit mRNA content at low blood ethanol concentrations, and increases at higher concentrations. These data suggest that differences between C57BL/6J and DBA/2J mice in the degree of physical dependence (withdrawal) on ethanol may be related to differential sensitivity to ethanol regulation of β₂ subunit expression.     

Development of in vivo somatic mutation system using antibody against hemoglobin Preparation and use of an anti-hemoglobin antibody for identifying C57BL/6 red cells in artificial mixture of DBA/2 and C57BL/6 red cells

A cellular specific-locus mutation test is described for detecting mutant cells in mammals. The test is based upon the use of specific anti-C57BL/6J mouse hemoglobin antibody that binds hemoglobin “single” (hemoglobin s, present in C57BL/6J mouse) and not hemoglobin “diffuse” (hemoglobin d, present in DBA/2J mouse). Attempts to purify such antibody from pony and rabbit antisera through cross-absorption were unsuccessful. Immunization of LP/J mouse with C57BL/6J hemoglobin produced antiserum that reacted with s hemoglobin but not with d hemoglobin. In a fluorescent antibody technique, this antibody was found to label fixed red blood cells from C57BL/6J mice but not from DBA/2J mice. In a mixture of C57BL/6J and DBA/2J red cells, the C57BL/6J cells could be differentiated by their bright fluorescence from the non-fluorescent DBA/2J cells. Reconstruction experiment with artificial mixtures of DBA/2J and C57BL/6J cells showed that s hemoglobin bearing cells could be detected in DBA/2J red cells at frequencies as small as 0.4×10^?6. Thus, the system is sensitive enough to detect d → s mutation in DBA/2J mice. Amino acid comparison of the globin chains of s and d hemoglobins shows that our antibody can probably detect mutations leading to a substitution of serine or proline by alanine at β²⁰ position and/or a substitution of threonine by alanine at β¹³⁹ position.