An improved technique for tail-cuff blood pressure measurements with dark-tailed mice.

Study of the genetics of hypertension has been facilitated greatly by the use of mice with modified genes that affect blood pressure. A current successful method for measuring blood pressure in mice relies on detection of light passing through the tail to determine the pressure in a tail-cuff necessary to stop pulsed flow. Success in obtaining reliable blood pressure measurements in light-tailed strains of mice (e.g., C57BL/6J) has been excellent. However, in our and others' experience, mice having highly pigmented tails (e.g., 129S6/SvEvTac) have yielded less consistent measurements. We report here that simple modifications to the channel containing the pulse detection sensor can greatly improve the pulse detection of dark-tailed mice. The first modification--lining the sensor channel with four layers of clear plastic wrap--increased the frequency of successful blood pressure measurements of 129S6/SvEvTac mice twofold and reduced variability by one-third. The second modification--lining the sides of the channel with reflective foil--also improved the success rate with dark-tailed mice. Mean blood pressures were unaffected by these modifications, which enhance detection of the pulse wave and likely will be helpful in diverse applications in which blood pressure is measured in rodent strains with pigmented tails.     

Innate immune response in Th1- and Th2-dominant mouse strains

C57BL/6 and BALB/c mice are prototypical Th1- and Th2-type mouse strains, respectively. In the present study, we attempted to characterize the innate immune response of macrophages from these mouse strains. Macrophages from C57BL/6 mice produced higher levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-12 than those from BALB/c mice after stimulation with macrophage-activating lipopeptide-2 (MALP-2, a synthetic TLR-2 ligand) or lipopolysaccharide (LPS, a TLR-4 ligand). The augmented IL-12 production by C57BL/6 macrophages increased interferon-gamma and, in contrast, decreased IL-13 production by CD4+ T cells. On stimulation with MALP-2 or LPS, C57BL/6 macrophages produced lysosomal enzyme and nitric oxide, effector molecules for bacterial killing, whereas BALB/c macrophages did not. Bactericidal activity of BALB/c macrophages was impaired relative to C57BL/6 macrophages when cells were infected with live bacteria in vitro. In a murine model of septic peritonitis induced by cecal ligation and puncture (CLP), BALB/c mice failed to facilitate bacterial clearance relative to C57BL/6 mice despite an augmented peritoneal leukocyte infiltration that was associated with increased peritoneal levels of cytokines/chemokines. BALB/c mice exhibited increased plasma and hepatic levels of cytokines/chemokines, resulting in an exaggerated systemic inflammation as determined by acute-phase proteins. Finally, BALB/c mice were vulnerable to CLP-induced lethality relative to C57BL/6 mice. Altogether, innate immune response of macrophages is different between these mouse strains, which may affect the development of Th1 and Th2 adaptive immunity in these strains. Reduced systemic inflammatory response in C57BL/6 mice that may result from an eminent local response appears to be beneficial during sepsis.     

Cmv-1, a genetic locus that controls murine cytomegalovirus replication in the spleen

The genetic basis of the control of acute splenic MCMV infection was studied after intraperitoneal inoculation of the virus. Classical Mendelian analyses using C57BL/6 (resistant) and BALB/c (susceptible) parental strains disclosed an autosomal dominant non-H-2 gene that regulates splenic virus replication. The probable location of this gene, to which we have assigned the symbol Cmv-1, is on chromosome 6 as defined by the strain distribution pattern of splenic MCMV replication in CXB recombinant inbred mice. Although there is a similar hierarchy of resistance to MCMV and HSV-1 with respect to the C57BL and BALB genetic backgrounds, the strain distribution pattern of HSV-1 replication in recombinant inbred mice suggests that Cmv-1 is not involved in restricting the spread of this virus. This is the first clear identification of a non-H-2 gene regulating the magnitude of MCMV infection. Elucidation of the function of this gene may be a fundamental step towards understanding the control of systemic CMV infection.     

Comparison of cigarette smoke-induced acute inflammation in multiple strains of mice and the effect of a matrix metalloproteinase inhibitor on these responses

The activities of proteases in the lung, specifically matrix metalloproteinases (MMPs), have been implicated in driving the inflammation and lung destruction observed in smokers with chronic obstructive pulmonary disease. Here, our aims were to compare the acute response with cigarette smoke exposure (CSE) in four mouse strains to identify common and distinguishing features and to assess the effect of an MMP inhibitor on this response. To do this, we exposed mice (BALB/C, C57BL/6, A/J, or 129/Sv) to whole-body CSE (1 h/day) for 3 days. CSE induced dose- and time-dependent increases in neutrophils and keratinocyte chemoattractant levels in the airways of all strains; however, the proportion of the neutrophilia differed among strains. In the two most contrasting strains, BALB/C and C57BL/6, we examined MMP gene expression and found only small changes apart from MMP-12, which was highly expressed in both strains. Both strains were then treated with a broad-spectrum MMP inhibitor, PKF242-484 [(2S,3R)-N(4)-((S)-2,2-dimethyl-1-methylcarbamoyl-propyl)-N(1)-hydroxy-2-hydroxymethyl-3-(4-methoxy-phenyl)-succinimide] (0.5-10 mg/kg) either orally or intranasally 1 h before and 5 h after CSE for 3 days. PKF242-484 dose-dependently reduced neutrophilia in BALB/C mice when dosed orally (p < 0.01) or intranasally (p < 0.01) but had no clear effect in C57BL/6 by either route. PKF242-484 reduced BAL macrophages when dosed intranasally (p < 0.05) but had no dose-dependent effect when dosed orally in both strains. These data suggest the inflammation induced by CSE is similar, but not identical, in different mouse strains. In addition, the ability of broad-spectrum MMP inhibitors to inhibit smoke-induced acute neutrophil inflammation is strain-dependent, whereas its ability to limit macrophage infiltration may be route dependent.     

Strain differences in basal and cocaine-evoked dopamine dynamics in mouse striatum

In vivo microdialysis was used to characterize basal dopamine (DA) dynamics and cocaine-evoked DA levels in the striatum of 129/Sv-ter, C57BL/6J, DBA/2J, and Swiss-Webster mice. Basal dialysate levels of DA did not differ in the four strains tested. Similarly, the no net flux method of quantitative microdialysis revealed no difference in extracellular levels between strains. However, the in vivo extraction fraction of DA was significantly less in 129/Sv-ter (53%) mice compared with C57BL/6J (68%), DBA/2J (69%), and Swiss-Webster (67%) mice, indicating a lower rate of basal DA uptake in the 129/Sv-ter strain. Perfusion of K(+) (60 and 100 mM) through the microdialysis probe significantly increased dialysate DA levels and there was no difference between strains in the magnitude of this effect. The acute administration of cocaine (5-20 mg/kg i.p.) increased DA levels in the four strains tested. Cocaine-evoked DA levels (in nanomoles) were significantly greater in 129/Sv-ter compared with C57BL/6J, DBA/2J, or Swiss-Webster mice after administration of either 5, 10, or 20 mg/kg cocaine. However, the percentage increase in DA did not differ across strains. These data demonstrate that there are strain-related differences in basal DA dynamics in the striatum of the mouse. Basal DA uptake was reduced in striatum of 129/Sv-ter mice compared with C57BL/6J, DBA/2J, or Swiss-Webster mice. In addition, the response of DA levels to cocaine may be enhanced in 129/Sv-ter compared with C57BL/6J, DBA/2J, or Swiss-Webster mice.     

Bacillus anthracis lethal toxin induces TNF-alpha-independent hypoxia-mediated toxicity in mice

Bacillus anthracis lethal toxin (LT) is the major virulence factor of anthrax and reproduces most of the laboratory manifestations of the disease in animals. We studied LT toxicity in BALB/cJ and C57BL/6J mice. BALB/cJ mice became terminally ill earlier and with higher frequency than C57BL/6J mice. Timed histopathological analysis identified bone marrow, spleen, and liver as major affected organs in both mouse strains. LT induced extensive hypoxia. Crisis was due to extensive liver necrosis accompanied by pleural edema. There was no evidence of disseminated intravascular coagulation or renal dysfunction. Instead, analyses revealed hepatic dysfunction, hypoalbuminemia, and vascular/oxygenation insufficiency. Of 50 cytokines analyzed, BALB/cJ mice showed rapid but transitory increases in specific factors including KC, MCP-1/JE, IL-6, MIP-2, G-CSF, GM-CSF, eotaxin, FasL, and IL-1beta. No changes in TNF-alpha occurred. The C57BL/6J mice did not mount a similar cytokine response. These factors were not induced in vitro by LT treatment of toxin-sensitive macrophages. The evidence presented shows that LT kills mice through a TNF-alpha-independent, FasL-independent, noninflammatory mechanism that involves hypoxic tissue injury but does not require macrophage sensitivity to toxin.     

Nociceptive and morphine antinociceptive sensitivity of 129 and C57BL/6 inbred mouse strains: implications for transgenic knock-out studies

Gene-targeting studies of pain, using transgenic 'knock-out' mice possessing null mutations of pain-relevant genes, are becoming increasingly common. This approach is a potentially powerful tool for the molecular dissection of complex traits such as pain modulation, but is subject to several theoretical drawbacks. One problem arises from the fact that the genetic background of knock-out mice is virtually always a mixture of alleles from two different strains; commonly 129 and C57BL/6. A more general caveat to knock-out findings derives from the demonstration that null mutations interact with genetic background to produce phenotypic changes. The present study investigated basal' nociceptive sensitivity (on the 49 degrees C tail-immersion/withdrawal test) and sensitivity to morphine antinociception in 129 and C57BL/6 mice (129/J, 129/Sv-+(p)+(Tyr-c)+(Mgf-SIJ), and C57BL/6J substrains). C57BL/6 mice displayed almost two-fold greater initial sensitivity to thermal stimulation than 129 mice, and three-fold reduced sensitivity to morphine inhibition of that noxious stimulus. These findings suggest that gene targeting studies of pain are particularly subject to the aforementioned concerns, and that C57BL/6 mice represent a suboptimal background strain for such efforts.     

GENETICS OF A NEW IgVH (T15 IDIOTYPE) MARKER IN THE MOUSE REGULATING NATURAL ANTIBODY TO PHOSPHORYLCHOLINE

The idiotype present on the Fab of a phosphorylcholine-binding IgA myeloma protein TEPC 15 (T15) of BALB/c origin was found in normal serum of BALB/c mice. Molecules carrying the T15 idiotype in normal serum could be adsorbed with Sepharose phosphorylcholine beads and R36A pneumococci. The T15 idiotype is absent in germ-free BALB/c but appears when the mice are conventionalized. A survey of normal sera of inbred strains for the T15 idiotype showed it to be present in BALB/c, 129, C57L, C58, and ST and absent or in low levels in CBA, C3H, C57BL/6, C57BL/Ka, C57BL/10, SJL, B10.D2, DBA/2, RIII, A, AL, AKR, NZB, and NH inbred strains of mice. The T15 idiotype is associated with some but not all strains carrying the IgC_H allotypes found in BALB/c. Linkage of genes controlling the T15 idiotype in normal serum to the IgC_H locus of BALB/c was demonstrated in F₂ progeny of a BALB/c and C57BL cross, Bailey's recombinant inbred strains, C x BD, C x BE, C x BG, C x BH, C x BI, C x BJ, C x BK, and CB20 congenic strains. Among these strains, only those possessing the IgC_H locus of BALB/c including the F₂ progeny consisting of BALB/c homozygotes and BALB/c/C57BL heterozygotes and C x BG and C x BJ recombinants showed the T15 idiotype.     

Immunological regulation of experimental cutaneous leishmaniasis. III. Nature and significance of specific suppression of cell-mediated immunity in mice highly susceptible to Leishmania tropica

BALB/c mice have been an exceptional susceptibility to Leishmania tropica infection such that cutaneous lesions grow without restraint in all cases leading to fatal metastasis and visceralization in normal and x-irradiated, bone-marrow reconstituted (XBM) animals. Adult thymectomized, x-irradiated, bone marrow-reconstituted (ATxXBM) BALB/c mice, however, show pronounced retardation of lesion growth leading to some survival and even cures. A similar trend was also found in moderately susceptible (BALB/c X C57BL/6)F1 mice, in contrast with the "resistant" CBA strain, in which, as previously known, ATxXBM animals showed impairment of normal, spontaneous self-healing. These convere effects are paralleled by respective leishmania-specific delayed-type hypersensitivity (DTH) reactivities, prior thymectomy leading to diminution in CBA and augmentation in BALB/c and (BALB/c X C57BL/6)F1. Anti-leishmanial DTH responses, amplfiable by cyclophosphamide pretreatment, can be detected in BALB/c mice within 10 d of infection with 2 X 10(7) promastigotes, but becomes near-totally suppressed by day 25-35. No such suppressin is found in CBA, C57BL/6, or (BALB/c X C57BL/6)F1 mice together with varying degrees of immune control of lesion development or regression. Suppression of DTH in BALB/c mice is leishmania specific and does not extent to 2,4-dinitrofluorobenzene (DNFB) or sheep erythrocytes specificities. Spleen cells from suppressed L. tropica-infected mice when transferred to normal BALB/c mice impaired the induction of DTH to leishmanial antigen. This property resided in the T cell-enriched fraction and not in the T cell- depleted fraction. It is concluded that a major component of the striking inability of BALB/c mice to control L. tropica infection involves profound impairment of a potentially curative cell-mediated immune response by suppressor T cell generation. The possibility is discussed that this may be secondary to rapid amastigote (antigen) accumulation in macrophages expressing the primary genetic "defect."     

Incidence and specificities of IgA and IgM anti-AgG autoantibodies in various mouse strains and colonies

Mice, greater than 20 wk old, were tested for the presence of anti-IgG autoantibodies by agglutination and radioimmunoassay. IgA and IgM anti- IgG were found in the 129/Sv, C57BL/6, and DBA/2 strains from the local colony at the International Institute of Cellular and Molecular Pathology (ICP), at the Institut Pasteur de Paris (IP), and in the endotoxin-resistant C3H/He strain of ICP. These strains were negative at Iffa Credo (IC), and at The Jackson Laboratory (JL). Among 33 strains from the latter colony, 129/J, AKR/J, CBA/J, C57L/J, and NZB/BinJ were positive. All were specific pathogen-free and, excepting the NZB/BinJ, are not known to develop systemic autoimmune disorders. These differences between colonies suggest an influence of the environment on the production of anti-IgG. Evidence for the role of an infectious agent was provided by the fact that germ-free DBA/2 were negative in contrast to their SPF relatives. Strains which were positive at ICP and IP for anti-IgG had four-times higher serum levels of total IgA and two-times higher levels of total IgG than the corresponding negative strains from IC and JL. The anti-IgG titers differed markedly from one strain to the other in the same environment; e.g., in mice from ICP, BALB/c mice produced 40-times less anti-IgG than 129/Sv. IgA anti-IgG occurred only in high producers of anti-IgG. In these animals, the proportion of IgA vs. IgM anti-IgG was very different from one group to the other; C57BL/6 had mainly IgM anti-IgG, DBA/2 mainly IgA anti-IgG, and 129/Sv both IgM and IgA anti-IgG. The IgA anti-IgG from 129/Sv, 129/J, NZB/BinJ, C57L/J, DBA/2, and C3H/He had restricted hetero-, iso-, and allotypic specificities. It reacted only with mouse IgGa2, but not with the Ig-1b allotype. C57BL/6 also had IgA anti-IgG with a narrow specificity, but directed against IgG1 without allotypic restriction. In contrast to the specificity of IgA anti-IgG, the antibody activity of IgM anti-IgG was much broader, except in the 129/Sv and 129/J strains where IgM anti-IgG shared the same narrow specificity with IgA.     

Strain-specific effects of amphetamine on prepulse inhibition and patterns of locomotor behavior in mice.

Several reports describe substantive behavioral differences between strains of mice both at baseline and in response to pharmacological manipulations. For example, mouse strain differences have been reported in prepulse inhibition (PPI) and patterns of locomotor activity, two behavioral processes that are altered by dopamine (DA) agonists such as amphetamine. Here, we characterized acoustic and tactile startle reactivity, acoustic PPI, and both the amounts and spatial patterns of locomotor activity in C57BL/6J, 129SvEv (129S6), and 129SvJ (129X1) mice at baseline and in amphetamine dose-response studies. Because hearing loss is common in numerous strains of mice, we also assessed cross-modal PPI using a light prepulse with an airpuff startle stimulus. The results establish that these three inbred strains of mice display both intra- and cross-modal PPI, and that amphetamine decreases PPI and startle reactivity in a dose-, sensory modality-, and strain-specific manner. Furthermore, the amount of locomotor activity and the spatial pattern of motor sequences are altered differentially after treatment with amphetamine in C57BL/6J and 129X1 mice, but not in 129S6 mice. Given that amphetamine releases presynaptic DA, these findings are consistent with the role of DA in the modulation of PPI and motor patterns in mice. These findings highlight the importance of selecting appropriate strains of mice for behavioral, pharmacological, and genetic studies.     

Susceptibility to Friend helper virus leukemias in CXB recombinant inbred mice

The seven CXB recombinant inbred strains were tested for susceptibility to Friend helper virus (F-MuLV) hematopoietic neoplasms. BALB/c and CXB- H mice develop erythroblastosis after neonatal inoculation with F-MuLV, while C57BL/6 and the six other RI strains develop lymphoma and myelogenous leukemia. This strain distribution pattern is different from that for H-2, Gpd-1 (linked to Fv-1), Fv-2, Rfv-3, and Cv (linked to Rmcf) but the same as that for Bv, the endogenous ecotropic virus of C57BL/6. However, analysis of crosses segregating Bv show that resistance to F-MuLV erythroblastosis is not linked to Bv. Disease-free survival is shortest for BALB/c mice, intermediate for CXB-H and CXB-J, and longest for C57BL/6 and the other RI strains. We conclude: (a) the major C57BL/6 gene for resistance to F-MuLV erythroblastosis is different from previously identified Friend virus restriction loci; (b) latency for F-MuLV leukemias is controlled by more than one gene; and (c) latency and susceptibility to F-MuLV erythroblastosis are not inherited concordantly in the CXB-RI strains.     

Cutaneous leishmaniasis. The defect in T cell influx in BALB/c mice

Local cellular responses to cutaneous infection with Leishmania mexicana amazonensis were examined in susceptible (BALB/c) and resistant (C57BL/6) mouse strains by immunocytochemical and electron microscopic studies. Infection during the first 8 wk in both animal strains was characterized by progressively enlarging lesions, epidermal thickening and ulceration, and accumulation of eosinophils and Ia+ infected macrophages. Healing of C57BL/6 mouse lesions began after 12 wk of infection and was associated with local influx of both Th (L3T4+) and T cytotoxic/suppressor (Lyt-2+) cells into the dermis, and Ia antigen expression on epidermal keratinocytes. T lymphocyte infiltration was marked and intracellular parasites were scarce by 21 wk of C57BL/6 infection. Similarly, granulomas in C57BL/6 livers contained L3T4+ and Lyt-2+ T lymphocytes and no visible intracellular parasites by 21 wk of infection. In contrast, BALB/c mouse lesions continued to enlarge and never healed. Throughout the entire course of infection, T lymphocyte influx into the heavily infected dermis was minimal. Keratinocyte Ia expression was absent in BALB/c lesions. BALB/c livers were heavily infected by 18 wk of cutaneous infection, with few demonstrable T lymphocytes. A systemic absence of T cells could not be demonstrated in BALB/c mice. Both L3T4+ and Lyt-2+ T cells were found in the peripheral blood in normal numbers in both mouse strains. Our results support the role of T cells as important local effector cells in the healing response of murine cutaneous leishmaniasis. We suggest that local T lymphocyte infiltration may provide lymphokines, particularly IFN-gamma, that can activate infected macrophages to destroy the intracellular parasites. Alternatively, T cells may play a cytotoxic role, killing infected macrophages and allowing local humoral factors to destroy released extracellular parasites.     

Genetically determined susceptibility and resistance to diet-induced atherosclerosis in inbred strains of mice

To determine whether recombinant inbred strains derived from C57BL/6J and A/J mice would provide a good model in which to study the genetics of diet-induced atherosclerosis, male mice of the parent strains were compared in a number of experiments designed to correlate various biochemical changes with susceptibility or resistance to the disease. In both strains fed an atherogenic diet containing 27% coconut oil and 4.5% cholesterol, there was a significant rise in serum very low-density plus low-density lipoprotein cholesterol levels, but only C57BL/6J mice developed discernible fatty lesions in the aortic wall. In A/J mice a significant rise in high-density lipoprotein cholesterol was also observed, which corresponded to the appearance of a second species of high-density lipoprotein in the serum, but in C57BL/6J mice there was a fall. In susceptible C57BL/6J mice, free cholesterol is secreted into bile, which becomes supersaturated, leading to the formation of gallstones. In the resistant strain, however, dietary cholesterol accumulates in the liver. A difference in hepatic cholesterol metabolism between the two strains may thus be a factor in determining their different susceptibilities to diet-induced atherosclerosis.     

Increased atherosclerosis in streptozotocin-induced diabetic mice.

Premature and extensive atheroscleroses involving renal, peripheral, and cardiovascular sites remain major complications of diabetes mellitus. Controversy exists as to the contribution of hyperglycemia versus elevated local or systemic concentrations of insulin to atherosclerosis risk. In this report, we developed the first murine model susceptible to both atherosclerosis and diabetes to determine which diabetogenic factors contribute to vascular disease. C57BL/6 and BALB/c mice were treated with multiple low-dose streptozotocin (STZ) or control citrate buffer and fed rodent chow or an atherogenic-promoting (Ath) diet for 12-20 wk. STZ treatment resulted in sustained hyperglycemia (250-420 mg/dl) and a modest reduction in plasma insulin levels for both strains regardless of diet. Citrate-treated C57BL/6 mice fed the Ath diet showed extensive oil red O-staining fatty streak aortic sinus lesions (20,537+/-2,957 micron2), the size of which did not differ for Ath-fed mice treated with STZ (16,836+/-2,136 micron2). In contrast, hyperglycemic BALB/c mice fed the Ath diet showed a 17-fold increase in atherosclerotic lesion area (7,922+/-2,096 micron2) as compared with citrate-treated mice fed the Ath diet (467+/-318 micron2). Correlations between lesion size and plasma glucose levels were significant for BALB/c (r = 0.741, P < 0.009), but not C57BL/6 (r = 0.314, P<0.3) mice. Lesion size correlated significantly with plasma cholesterol for C57BL/6 (r = 0.612, P<0.03) but not BALB/c (r = 0.630, P<0.1) mice. Immunohistochemistry showed that aortic sinus lesions from both strains contained macrophages, but smooth muscle cells were clearly present in lesions of BALB/c mice. In summary, we present the first small animal model showing accelerated atherosclerosis in response to hyperglycemia. Fatty streaks resembled those of human type II lesions in that both macrophages and smooth muscle cells were evident. In addition, our results support the concept that hyperglycemia as opposed to hyperinsulinemia contributes heavily to risk of atherosclerosis.     

Genetic heterogeneity in the toxicity to systemic adenoviral gene transfer of interleukin-12

Despite the efficacy of IL-12 in cancer experimental models, clinical trials with systemic recombinant IL-12 showed unacceptable toxicity related to endogenous IFNgamma production. We report that systemic administration of a recombinant adenovirus encoding IL-12 (AdCMVmIL-12) has a dramatically different survival outcome in a number of mouse pure strains over a wide range of doses. For instance at 2.5 x 10(9) p.f.u., systemic AdCMVmIL-12 killed all C57BL/6 mice but spared all BALB/c mice. Much higher IFNgamma concentrations in serum samples of C57BL/6 than in those from identically treated BALB/c were found. Causes for heterogeneous toxicity can be traced to differences among murine strains in the levels of gene transduction achieved in the liver, as assessed with adenovirus coding for reporter genes. In accordance, IL-12 serum concentrations are higher in susceptible mice. In addition, sera from C57BL/6 mice treated with AdCMVmIL-12 showed higher levels of IL-18, a well-known IFNgamma inducer. Interestingly, lethal toxicity in C57BL/6 mice was abolished by administration of blocking anti-IFNgamma mAbs and also by simultaneous depletion of T cells, NK cells, and macrophages. These observations together with the great dispersion of IFNgamma produced by human PBMCs upon in vitro stimulation with IL-12, or infection with recombinant adenovirus encoding IL-12, suggest that patients might also show heterogeneous degrees of toxicity in response to IL-12 gene transfer.     

GRAFT-VS.-HOST REACTIONS IN RECIPROCAL HYBRID MICE : I. DISSOCIATION OF T-CELL ACTIVITIES IN THE MIXED LYMPHOCYTE REACTION AND TWO GRAFT-VS.-HOST ASSAYS

Spleen cells from BALB/c and C57BL/6 mice were tested for their reactivity against reciprocal hybrid tissues ((BALB/c x C57BL/6) F₁ and (C57BL/6 x BALB/c) F₁) in three assay systems: the mixed lymphocyte reaction (MLR); the Simonsen spleen-weight graft-vs.-host (GVH) assay; and a GVH mortality assay. It was shown that both F₁'s serve as equally effective stimulators of parental cells in the MLR. In the spleen-weight assay, BALB/c and C57BL/6 cells were equally active in a given host, but greater splenomegaly was observed in (BALB/c x C57BL/6) F₁ hosts regardless of the donor strain. By contrast, BALB/c cells were much less lethal than C57BL/6 cells in (BALB/c x C57BL/6) F₁ hosts than in (C57BL/6 x BALB/c) F₁ hosts, and to a lesser degree C57BL/6 cells were less lethal than BALB/c cells in (C57BL/6 x BALB/c) F₁ hosts. The possibility that modifying substances may differentially alter reactivity of parental lymphocytes and that considerations other than genotype determine the outcome of a GVH reaction are discussed in detail.     

Differential expression of an equivalent clonotype among BALB/c and C57BL/6 mice

The primary anti-phosphorylcholine (PC) response in BALB/c, C57BL/6, and congenic and recombinant inbred strains of these parental types has been examined in the splenic focus system. The frequencies of PC-specific precursors were shown to vary among these strains from 2 to 20 precursors per 10(6) splenic B cells. The distribution of these frequencies suggests that elements closely linked to or within the major histocompatibility complex may play a role in the determination of this parameter, although additional experiments are necessary to adequately assess this possibility. Moreover, all strains tested, regardless of immunoglobulin allotype, expressed monoclonal antibodies indistinguishable from the TEPC 15 myeloma protein (T15) clonotype. Further, the frequency of this clonotype in a given strain did not appear related to allotype, since both high and low T15 frequencies were found among strains of either the BALB/c (a(1)) or C57BL/6 (a(2)) allotype. The examination of normal serum for the T15 idiotype, however, revealed that only mice of the BALB/c allotype (a(1)) expressed the T15 idiotype in detectable quantities. After immunization with Diplococcus pneumoniae, sera from mice of the a(1) allotype consistently contained large quantities of the T15 idiotype, whereas sera from mice of the a(2) allotype exhibited various degrees of cross-reactivity with anti-T15 antibody. These results suggest that: (a) the allotype of an individual, although closely related to serum levels of an idiotype, is unrelated to the proportion of the precursor population which expresses that idiotype and; (b) the serum expression of a given idiotype may reflect regulatory processes, which act either during or before antigenic stimulation, rather than the actual clonotype representation in the repertoire. These findings indicate that distinctions must be made between the expression of idiotypic determinants within precursor B-cell populations and elements which regulate the subsequent appearance of those idiotypes in serum antibodies.     

GENETICS OF RESTRICTED ANTIBODIES TO STREPTOCOCCAL GROUP POLYSACCHARIDES IN MICE : I. STRAIN DIFFERENCES OF ISOELECTRIC FOCUSING SPECTRA OF GROUP A HYPERIMMUNE ANTISERA

The immune response of nine inbred and one outbred strain of mice to the streptococcal group A polysaccharide was investigated with respect to magnitude and restriction. Analytical isoelectric focusing served as a tool to estimate the degree of restriction of Group A polysaccharide-specific antibodies. It proved feasible to distinguish low and intermediate from high responder strains, and to delineate strain-specificity of isoelectric focusing spectra of the immune sera. For example, immune sera of BALB/c mice, restricted high responders, and of C57BL/6 mice, heterogeneous low responders, had distinct focusing properties. Responsiveness was a dominant autosomal genetic trait in C57BL/6 x BALB/c F₁ hybrid mice, irrespective of the maternal and the paternal genotype; the immune sera of these mice had their own, rather uniform isoelectric focusing spectra whereby structural genes of the low responder strain were expressed to predominant levels in 81% of the hybrids. Responsiveness in C57BL/6 x BALB/c F₂ progeny segregated into 79% high and 21% low responders, and showed no genetic linkage to the following characteristics: hair color, sex, H-2 type, and Ig allotype of the heavy chain. The isoelectric focusing properties of these immune sera indicated segregation into patterns like BALB/c mice (40%), F₁ hybrids (48%), and C57BL/6 mice (12%). Since this segregation is independent of any of the above criteria in these F₂ mice a regulatory gene(s) is postulated that controls the clonal pattern of the immune response.