Genetic linkage between the AH locus and a major gene that inhibits susceptibility to audiogenic seizures in mice

Mice of the DBA/2 (D2) strain are highly susceptible to sound-induced seizures at 21 days of age; whereas, mice of the C57BL/6 (B6) strain are resistant to these seizures. Although the difference in susceptibility to audiogenic seizures (ASs) between these two strains is inherited as a multiple-factor trait, an association was observed between susceptibility to ASs and the Ah locus. The Ah locus controls the inducibility of aryl hydrocarbon hydroxylase (AHH) activity by a number of aromatic hydrocarbons. B6 mice carry the Ahb allele and have inducible AHH activity; whereas, D2 mice carry the Ahd allele and have noninducible activity. Inducibility is inherited as a Mendelian dominant trait in crosses between these strains. Mice carrying the Ahb allele are generally less susceptible to ASs sat 21 days of age than are mice carrying the Ahd allele. The combined results from B6 X D2 recombinant inbred strains, congenic strains (where the Ahb allele was placed into the D2 genome and the Ahd allele placed into the B6 genome), the B6D2F1 X D2 backcross generation, and a random survey of various inbred strains, suggest that the association between these two traits is due to genetic linkage, rather than to pleiotrophy or to chance. A major gene that inhibits susceptibility to ASs appears to be closely linked to the Ah locus. This gene has been designated Ias, for inhibition of ASs. A large portion of the genetic variability of AS susceptibility may be due to the segregation of Ias.     

Cdkn2a, the cyclin-dependent kinase inhibitor encoding p16INK4a and p19ARF, is a candidate for the plasmacytoma susceptibility locus, Pctr1

Plasma cell tumor induction in mice by pristane is under multigenic control. BALB/c mice are susceptible to tumor development; whereas DBA/2 mice are resistant. Restriction fragment length polymorphisms between BALB/c and DBA/2 for Cdkn2a(p16) and Cdkn2b(p15), and between BALB/c and Mus spretus for Cdkn2c(p18(INK4c)) were used to position these loci with respect to the Pctr1 locus. These cyclin-dependent kinase (CDK) inhibitors mapped to a 6 cM interval of chromosome 4 between Ifna and Tal1. C.D2-Chr 4 congenic strains harboring DBA/2 alleles associated with the Pctr1 locus contained DBA/2 "resistant" alleles of the CDK4/CDK6 inhibitors p16 and p15. On sequencing p16 and p18 cDNAs, two different allelic variants within ankyrin repeat regions of p16 were found between BALB/c and DBA/2 mice. By using an assay involving PCR amplification and restriction enzyme digestion, allelic variants were typed among several inbred strains of mice. One of the variants, G232A, was specific to two inbred strains, BALB/cAn and ABP/Le, of mice and occurred in a highly conserved amino acid in both human and rat p16. When tested with wild-type (DBA/2) p16, both A134C and G232A BALB/c-specific variants of p16 were inefficient in their ability to inhibit the activity of cyclin D2/CDK4 in kinase assays with retinoblastoma protein, suggesting this defective, inherited allele plays an important role in the genetic susceptibility of BALB/c mice for plasmacytoma induction and that p16(INK4a) is a strong candidate for the Pctr1 locus.     

A novel V beta 2-specific endogenous mouse mammary tumor virus which is capable of producing a milk-borne exogenous virus

We have previously reported new Mtv loci, Mtv-48 and -51, in the Japanese laboratory mouse strains CS and NC. Here we show by backcross analysis that both Mtv-48 and -51 cosegregate with very slow deletion of T cells bearing V beta 2. The nucleotide sequences of the open reading frames in the 3' long terminal repeats of Mtv-48 and -51 were very similar to those of Mtv-DDO, mouse mammary tumor virus C4 [MMTV(C4)], and MMTV(BALB/cV), which encode V beta 2-specific superantigens. Furthermore, backcross female mice carrying Mtv-48 but not Mtv-51 were found to be able to produce milk-borne MMTV(CS), which can vigorously stimulate V beta 2-expressing T cells after local injection in vivo in an I-E-dependent manner. On the other hand, mice carrying Mtv-51 but not Mtv-48 could not produce such an MMTV in milk. The nucleotide sequences of MMTV(CS) open reading frame were completely matched with those of Mtv-48. These results indicate that the provirus Mtv-48 but not Mtv-51 is capable of producing a milk-borne virus of which the superantigen stimulates V beta 2-expressing T cells.     

Efficient presentation of endogenous superantigen by H-2Aq

Endogenous superantigens encoded by mouse mammary tumor viruses associate with MHC class II and interact with T cells bearing particular V beta gene segments. H-2E is more efficient at presentation than H-2A, indeed Aq has not been shown to be capable of presenting endogenous superantigens. Atypically, the superantigen vSAG-3 encoded by Mtv-3 is presented efficiently in non-obese diabetic (H-2g7) mice by H-2A; we have examined the independent contributions of vSAG-3 and Ag7 to this process. Ag7 was not found to have a more general ability to efficiently present endogenous superantigens other than Mtv-3. Examination of Mtv-3-mediated thymic deletion of V beta 3+ thymocytes in the presence of H-2q additionally demonstrated the efficient presentation of vSAG-3 by Aq. Interaction of vSAG-3 with Aq and Ag7 is likely to reflect the unique sequence of Mtv-3 within the second polymorphic region previously implicated in MHC class II binding. The demonstration that mouse endogenous superantigens can be presented by a wider range of MHC haplotypes than previously thought is further evidence for their immunological impact on the mouse population.     

Resistance to polyoma virus-induced tumors correlates with CTL recognition of an immunodominant H-2Dk-restricted epitope in the middle T protein

The natural mouse pathogen polyoma virus is highly oncogenic in H-2k mice carrying the endogenous superantigen encoded by the mouse mammary tumor provirus Mtv-7. This superantigen results in deletion of Vbeta6 TCR-expressing polyoma-specific CD8+ CTL, which appear to be critical effectors against polyoma tumorigenesis. Here we have isolated cloned lines of CD8+ T cells from resistant (i.e., Mtv-7-) H-2k mice that specifically lyse syngeneic polyoma virus-infected cells and polyoma tumor cells. Nearly all these CTL clones express Vbeta6 and are restricted in their recognition of virus-infected cells by H-2Dk. Screening a panel of synthetic peptides predicted to bind to Dk, for which no consensus peptide binding motif is known, we identified a peptide corresponding to a nine-amino acid sequence in the carboxyl-terminus of the middle T (MT) protein (amino acids 389-397) that was recognized by all the Vbeta6+ CD8+ CTL clones. The inability of MT(389-397)-reactive CTL to recognize cells infected with a mutant polyoma virus encoding a MT truncated just proximal to this sequence indicates that MT(389-397) is a naturally processed peptide. The frequencies of precursor CTL specific for polyoma virus and MT(389-397) peptide were similar, indicating that MT(389-397) is the immunodominant epitope in H-2k mice. In addition, polyoma-infected resistant mice possess a 10- to 20-fold higher MT(389-397)-specific precursor CTL frequency than susceptible mice. This highly focused CTL response to polyoma virus provides a valuable animal model to investigate the in vivo activity of CTL against virus-induced neoplasia.     

Listeria monocytogenes-infected human umbilical vein endothelial cells: internalin-independent invasion, intracellular growth, movement, and host cell responses

Tissue concentrations of mercury were determined by cold vapor atomic absorption spectrometry in different inbred mouse strains after continuous treatment with HgCl2 (3 weekly sc injections of 0.5 mg/kg bw) for up to 12 weeks. Except for the thymus, in which steadily increasing mercury concentrations were found, in steady state levels of mercury were reached in blood and liver after 4 weeks and in spleen and kidney after 8 weeks. In the closely related strains C57BL/6, B10.D2, and B10.S, which differ only or primarily at the major histocompatibility complex, mercury concentrations in blood and liver were about twofold lower and renal concentrations were about three- to fivefold lower than those detected in strains A.SW and DBA/2. Another strain difference was observed in the spleen: after 8 and 12 weeks of continuous HgCl2 treatment, mercury concentrations in the spleen of strains A.SW, C57BL/6, and B10.S were significantly higher than those in strains DBA/2 and B10.D2. The strain difference in the spleen, an organ of the immune system, correlates with the susceptibility to the HgCl2-induced systemic autoimmune syndrome in mice in that the strains showing a higher mercury accumulation in the spleen are susceptible to this form of chemically induced autoimmunity, whereas the strains with lower mercury concentrations in the spleen are resistant.     

The plasmacytoma resistance gene, Pctr2, delays the onset of tumorigenesis and resides in the telomeric region of chromosome 4

Mouse plasmacytomas share pathogenetic features in common with both multiple myeloma and Burkitt's lymphoma in humans. Susceptibility to plasmacytoma induction by intraperitoneal pristane in mice is controlled by multiple genes. At least two of these genes reside on mouse chromosome 4 in regions of the genome sharing linkage homology with human chromosomes 9p21, 1p32, and 1p36. A series of congenic strains recombinant for regions of mouse chromosome 4 in the vicinity of the Pctr2 predisposition locus were created and typed for their tumor susceptibility/resistance phenotypes. These strains were derived by introgressively backcrossing alleles from resistant DBA/2 mice onto the susceptible BALB/cAnPt background. Six resistant and two susceptible strains were allelotyped for 10 genes and 49 random DNA markers to identify the smallest region of overlap in the resistant strains. These studies have determined that the Pctr2 locus resides in either a 500-kb interval proximal to Nppa, or in a 1- to 2-centiMorgan (cM) interval distal to Nppa. In these congenic strain analyses, the Nppa and Fv1 loci, in addition to genes within about 1 cM of these loci, have been excluded as candidates for the Pctr2 locus. A relevant locus that may reside in this interval is Rep2; it is associated with the efficiency of repairing X-ray induced DNA damage sustained during the G2 phase of the mitotic cycle. The Pctr2 locus acts in a codominant fashion. F1 hybrids between resistant and susceptible congenic strains exhibit a reduced tumor incidence and a significant delay in the onset of tumorigenesis. Identification and eventual cloning of the Pctr2 locus may assist in the identification of genes involved in many types of cancer showing aberrations in human chromosome 1p36.     

Intrinsic and extrinsic control of hemopoietic stem cell numbers: mapping of a stem cell gene

We evaluated in vivo interactions between extrinsic (growth factor induced) and intrinsic (genetically determined) effectors of mouse primitive hemopoietic stem cell proliferation and numbers. Accordingly, stem cell frequency and cell cycle kinetics were assessed in eight strains of inbred mice using the cobblestone area-forming cell (CAFC) assay. A strong inverse correlation was observed between mouse lifespan and the number of autonomously cycling progenitors (CAFC day 7) in the femur. The population size of primitive stem cells (CAFC day 35) varied widely (up to sevenfold) among strains, unlike total CAFC day 7 numbers (cycling and quiescent), which were similar. Administration of the early acting cytokine flt-3 ligand to these strains resulted in activation of quiescent primitive stem cells exclusively in strains with high endogenous stem cell numbers (DBA and AKR), but was unrelated to strain-specific progenitor cell cycling. To map loci affecting stem cell frequency, we quantified stem cells in BXD recombinant inbred mice (offspring of C57BL/6 and DBA/2). The resulting strain distribution pattern showed high concordance with a marker that mapped to chromosome 18 (19 cM). Linkage with this genomic interval was associated with a likelihood of odds score of 3.3, surpassing the level required for significance. Interestingly, this segment, containing the EGR-1 gene, shows synteny with human chromosome 5q, a region strongly associated with various hematological malignancies. Our findings indicate that a gene mapping to this region is mutated in either C57BL/6 or DBA/2 (and possibly AKR) mice. These studies in apparently healthy mice may facilitate the identification of a gene implicated in human 5q-syndromes.     

Heterogeneity of the T cell response to immunodominant determinants within hen eggwhite lysozyme of individual syngeneic hybrid F1 mice: implications for autoimmunity and infection

Hybrid F1 mice derived from inbred parental mouse strains are extensively used as animal models of human autoimmune diseases and transplantation. It is generally believed that with regard to immunologic studies, hybrid F1 mice behave in a consistent manner, equivalent to any other inbred mouse strain. In this study, we report that in comparison to inbred parental strains, individual hybrid F1 mice revealed a broad heterogeneity of proliferative response to the immunodominant determinants within hen eggwhite lysozyme (HEL). Of five parental strains tested, individual mice of three strains responding to only a few dominant HEL determinants (B6, BALB/c, and B10.PL) showed quite homogeneous patterns of response, whereas two mouse strains responsive to several determinants of HEL revealed either relative homogeneity (CBA/J mice) or heterogeneity (SJL mice) of response. However, in SJL mice, responses to major, dominant determinants of HEL were quite consistent. On the contrary, regardless of the consistency of response of parental strains, all three of F1 mice [[B6 x BALB/c]F1, [B6 x CBA/J]F1, and [SJL x B10.PL]F1] revealed significantly greater heterogeneity of response, which even involved the major, dominant determinants of HEL. We attribute the above heterogeneity of response to the competitive as well as aleatory nature of the interaction between various factors, including the coexistence of different MHC (parental as well as hybrid MHC) molecules, determinant capture, and the T cell repertoire. These results have important implications for studies on autoimmunity, infection, and vaccine design in human populations, where heterozygosity is the norm rather than the exception.     

T helper 2-dominant antilymphoma immune response is associated with fatal outcome

The precise role of the endogenous immune system in modulating cancer development remains unclear. Tumor cells are generally thought to be nonimmunogenic because they are of 'self' origin. However, tumor-reactive lymphocytes can be isolated from patients with many types of cancer. It is unclear what role these lymphocytes play and why they fail to protect the host. Using a murine B-cell leukemia/lymphoma (BCL1) model, we showed the development of a vigorous antitumor T-cell response in the tumor-susceptible host. Specific T-cell responses against BCL1 developed as early as day 4. However, the nature of this nonprotective response is different from the protective response produced in a major histocompatibility complex-matched tumor-resistant host. Susceptible hosts developed a T helper 2 (Th2)-dominant response, whereas resistant hosts developed a Th1-dominant response to BCL1. Cytolytic activity against BCL1 developed in both resistant and susceptible hosts, but in the susceptible host, this response was weaker and delayed compared with that in the resistant host. Thus, tumor susceptibility does not necessarily mean the absence of an antitumor immune response. Rather, the nature of the antitumor immune response is critical in determining clinical outcome.     

Effects of alcohol on acquisition and retention of passive-avoidance conditioning in different mouse strains.

270 male Ss of the C57BL/6 and DBA/2 inbred mouse strains and of the F1 hybrid of these 2 were trained and tested in a passive-avoidance task under 0-3 gm/kg doses of ethanol. The C57 Ss performed better in acquisition at higher alcohol doses than either the DBA or hybrid Ss. The hybrids showed retention the following day at higher doses than either of the parental strains. The DBA and C57 Ss showed evidence of state-dependent learning at some alcohol doses while the hybrid mice did not. Low doses markedly disinhibited DBA mice in initial exploratory behavior, so that they became identical in this parameter to the other strains which were not so affected. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detection of immunoglobulin/c-myc recombinations in mice that are resistant to plasmacytoma induction

Interchromosomal recombinations between c-myc and immunoglobulin sequences can be found in preneoplastic lesions (oil granulomata) during pristane-induced plasmacytoma development in susceptible BALB/cAn mice. In this study we used a more sensitive approach, hybridization-enriched templates with nested PCR, to detect microclones with Ig alpha/c-myc recombinations in oil granulomata of susceptible and resistant mice. Recombinations were detected in as many as 73% (32/44) of plasmacytoma-susceptible BALB/cAn mice 30 days after an injection of pristane. Mice that are resistant to plasmacytoma induction can also harbor recombination-positive cells, but these are less frequent [2/20 DBA/2N, 8/20 (BALB/cAn x DBA/2N)F1, hereafter called CD2F1]. The clones in DBA/2N mice were small (< 400 cells), whereas in BALB/cAn, the oil granuloma harbored up to several thousand of these cells. We conclude that the molecular machinery for generating characteristic interchromosomal recombinations can be found in all strains of mice. Both the frequency of generating Ig alpha/c-myc recombinations and the expansion of recombination-positive cells are greater in susceptible mice than in resistant strains.     

Immunosuppressive effects of 3-methylcholanthrene given intratracheally in various inbred strains of mice

The immunosuppressive effects of 3-methylcholanthrene (MCA) given intratracheally have been shown to correlate with susceptibility of some inbred strains of mice to MCA-induced carcinogenesis. In susceptible strains of mice, C3Hf and C57BL/6, intratracheal administration of MCA resulted in profound systemic immunodepression. This effect was not observed in resistant DBA/2 mice. This immunodepressive effect correlated with the inducibility of the aryl hydrocarbon hydroxylase enzyme complex and the inducibility of pulmonary tumors by MCA.     

Sex-restricted non-Mendelian inheritance of mouse chromosome 11 in the offspring of crosses between C57BL/6J and (C57BL/6J x DBA/2J)F1 mice

We report on the observation of sex-restricted, non-Mendelian inheritance over a region of mouse Chromosome (Chr) 11, occurring in the offspring of crosses between two commonly used Mus musculus-derived inbred strains, C57BL/6J and DBA/2J. In the surviving backcross progeny of reciprocal matings between (C57BL/6J x DBA/2J)F1 hybrids and the C57BL/6J parental strain, we observed the preferential appearance of C57BL/6J alleles along a region of Chr 11. The deviation from Mendelian predictions was observed only in female offspring from both reciprocal backcrosses, and not in males from either cross. The sex-specificity of the observed non-Mendelian inheritance points to an explanation based on embryonic or neonatal lethality. Our data add to previously obtained evidence for a Chr 11 locus or loci with sex-specific and allele-specific effects on viability.     

Painful neuropathies

Mercury can induce systemic autoimmunity in susceptible mouse strains characterized by a T-cell-dependent polyclonal B-cell activation, increased serum levels of IgG1 and IgE antibodies, production of autoantibodies, and the formation of immune complexes in the kidneys. However, certain resistant mouse strains do not show any of the autoimmune manifestations after mercury injection. Th1/Th2 dichotomy has been proposed to be responsible for resistance and susceptibility, respectively. Immunosuppression has also been suggested in resistant animals after mercury injection. To test whether immunosuppression or a biased Th1-type response was induced by mercury in resistant DBA/2 mice, we injected DBA/2 mice with mercury for 1 or 3 weeks and then immunized the mice with horse red blood cells (HRBCs) to study whether the subsequent humoral response to HRBCs was inhibited or skewed to the production of antibodies of IgG2a isotype switched by Th1-type cytokines. We found that there was no reduction of the number of splenic antibody-producing cells in the subsequent response to HRBCs compared with saline-treated mice. By haemagglutination tests, the titers of HRBC-specific antibodies were the same after HRBCs injection in both mercury- and saline-treated DBA/2 mice. There was no increase in total serum IgG2a antibody. Sera of both mercury- and saline-treated mice immunized with HRBCs showed high titres of specific IgM, IgG1 and IgG2a anti-HRBCs antibodies. Surprisingly, 3-week treatment with mercury induced a reduction in the titres of specific IgG2a anti-HRBCs antibodies in DBA/2 mice after immunization with HRBCs. Our results demonstrated that mercury did not induce a general immunosuppression or a biased Th 1-type immune response in resistant DBA/2 mice. The nonresponsiveness in mice resistant to mercury-induced autoimmunity must be due to some other unknown mechanism(s).     

Bone marrow cell response following induction of acute inflammation in different strains of mice

The magnitude of the macrophage inflammatory response differs among inbred mouse strains. Mice of the A/J strain respond poorly to sterile inflammatory stimuli while those of the C57BL/6 strain show a strong response. Inflammatory macrophages found at the site of inflammation are the product of bone marrow (BM) myeloid stem cells. Mice of the A/J strain were found to have half the number of BM nucleated cells per femur than those of the C57BL/6 strain. The lower BM cellularity may be one reason for the poor macrophage inflammatory response observed in A/J mouse strain. Using A x B/B x A recombinant inbred mouse strains, we determined that the number of nucleated cells per femur found in normal mice was not a determining factor of the magnitude of the macrophage inflammatory response. One additional explanation for the poor macrophage inflammatory response in mice of the A/J strain is their deficiency in the C5 component of complement. Using a C5-sufficient A/J.C5 congenic strain, we have previously shown that the presence of C5 on the A/J background improved their inflammatory response. We compared A/J and A/J.C5 mouse strains to determine whether or not C5 had an impact on the BM cell response to inflammatory stimulus. The presence of C5 on the A/J background could contribute to the improvement of the inflammatory response in mice of the A/J.C5 strain by inducing a greater number of nucleated cells to exit the BM compartment early following induction of inflammation.     

Activation of natural killer cells in arthritis-susceptible but not arthritis-resistant mouse strains following Borrelia burgdorferi infection

Infection of susceptible mouse strains with Borrelia burgdorferi, the agent of Lyme disease, results in the development of arthritis. Components of the innate immune system may be important mediators of this pathology. To investigate the potential role of NK cells in development of experimental Lyme arthritis, we examined their activation in vivo in both resistant and susceptible mouse strains. Following inoculation of B. burgdorferi into the footpad, lymph node NK cells from susceptible C3H/HeJ (C3H) mice produced more gamma interferon than NK cells from resistant DBA/2J mice. Lymph node cells from susceptible C3H and AKR mice also had increased ability to lyse YAC-1 target cells 2 days following infection. Antibody depletion of NK cells from susceptible mice, however, did not alter the development of arthritis following B. burgdorferi challenge. In addition, NK cell depletion had little effect on spirochete burden. Thus, there is a marked activation of NK cells in susceptible mouse strains following infection. Although NK cells are not absolutely required for arthritis, events occurring prior to NK cell activation might be important in mediating pathology in experimental Lyme disease.     

A locus on chromosome 7 determines myocardial cell necrosis and calcification (dystrophic cardiac calcinosis) in mice

Dystrophic cardiac calcinosis, an age-related cardiomyopathy that occurs among certain inbred strains of mice, involves myocardial injury, necrosis, and calcification. Using a complete linkage map approach and quantitative trait locus analysis, we sought to identify genetic loci determining dystrophic cardiac calcinosis in an F2 intercross of resistant C57BL/6J and susceptible C3H/HeJ inbred strains. We identified a single major locus, designated Dyscalc, located on proximal chromosome 7 in a region syntenic with human chromosomes 19q13 and 11p15. The statistical significance of Dyscalc (logarithm of odds score 14.6) was tested by analysis of permuted trait data. Analysis of BxH recombinant inbred strains confirmed the mapping position. The inheritance pattern indicated that this locus influences susceptibility of cells both to enter necrosis and to subsequently undergo calcification.