Properties of reticulum cell sarcomas in SJL/J mice

While T cells from SJL and from F₁ hybrids of SJL that do not express I-E antigens give strong proliferative responses to RCS, T cells from F₁ hybrids expressing surface I-E do not. The nature of the stimulating antigen on the RCS cell surface was examined using monoclonal antibodies. Complete inhibition of the T-cell proliferative response was obtained with antibodies to I-A antigens, whereas antibodies to I-E antigens did not inhibit at all. This inhibition was mediated via an effect of the antibodies on the stimulating cells. Biochemical characterization of immunoprecipitated ¹²⁵I- and 's S-labeled RCS antigens was performed using two-dimensional gel electrophoresis. Using this technique, I-A antigens were readily detected. However, neither Ia.7-specific antibodies nor antibodies specific for E_α : E _β complexes precipitated any E alpha or E beta chains. Comparison of I-A antigens from RCS and normal SJL spleen cells revealed minor mobility differences in the gels, possibly due to differences in glycosylation, the significance of which needs to be further evaluated. Examination of RNA extracted from RCS, using E alpha and A alpha cDNA probes showed that RCS cells do not transcribe the E alpha gene as has been shown previously for normal H-2 ^s cells. Furthermore, DNA from RCS cells showed a defect in the E alpha gene similar to that known to exist in normal H-2 ^s cells. Our findings exclude the presence of E alpha on RCS cells and suggest a major role for I-A, either alone or in conjunction with another as yet unidentified cell surface antigen, in the stimulation of T cells.     

Characterization of T cell lines and clones from SJL/J and (BALB/c x SJL/J)F1 mice specific for myelin basic protein

Lines of thymus-derived lymphocytes reactive against bovine myelin basic protein (BP) were established in vitro from SJL/J mice. These lines are stable in long-term culture and mediate inflammatory central nervous system (CNS) lesions and a low incidence of clinical experimental allergic encephalomyelitis (EAE) when injected into recipient SJL/J mice. The line cells proliferate in response to BP of bovine, rat, or mouse origin. Clones were derived from these lines, and the characteristics of these clones were analyzed. The clones express Thy-1, Ly-1, and L3T4 antigens and are negative for Ly-T2. The clones all proliferate in response to bovine BP, with different clones showing varying degrees of cross-reactivity between bovine, rat, and mouse BP. The proliferative response is MHC-restricted; antigen-presenting cells from I-As strains are required. Compatible with their phenotype as helper cells, some of the clones will provide help to primed B cells stimulating antibody production in an in vitro assay. When injected into recipients pretreated with pertussis and irradiation, clones that showed proliferation to mouse BP induced the development of inflammatory lesions in the CNS, with mortality of 28% of the recipients. T cell lines were also established in (BALB/c x SJL/J)F1 mice. In contrast to the homozygous SJL/J lines, these lines were highly encephalitogenic, inducing a high incidence of clinical and histologic EAE when injected in vivo.     

Cellular differences in the regeneration of murine skeletal muscle: a quantitative histological study in SJL/J and BALB/c mice

Summary Skeletal muscle regeneration in SJL/J and BALB/c mice subjected to identical crush injuries is markedly different: in SJL/J mice myotubes almost completely replace damaged myofibres, whereas BALB/c mice develop fibrotic scar tissue and few myotubes. To determine the cellular changes which contribute to these differential responses to injury, samples of crushed tibialis anterior muscles taken from SJL/J and BALB/c mice between 1 and 10 days after injury were analysed by light and electron microscopy, and by autoradiography. Longitudinal muscle sections revealed about a 2-fold greater total mononuclear cell density in SJL/J than BALB/c mice at 2 to 3 days after injury. Electron micrographs identified a similar proportion of cell types at 3 days after injury. Autoradiographic studies showed that the proportions of replicating mononuclear cells in both strains were similar: therefore greater absolute numbers of cells (including muscle precursors and macrophages) were proliferating in SJL/J muscle. Removal of necrotic muscle debris in SJL/J mice was rapid and extensive, and by 6 to 8 days multinucleated myotubes occupied a large part of the lesion. By contrast, phagocytosis was less effective in BALB/c mice, myotube formation was minimal, and fibrotic tissue conspicuous. These data indicate that the increased mononuclear cell density, more efficient removal of necrotic muscle, together with a greater capacity for myotube formation in SJL/J mice, contribute to the more successful muscle regeneration seen after injury.     

Opsonization of tumor-reactive T cells in SJL/J mice bearing syngeneic tumors

Summary The role of antigen-reactive cell opsonization (ARCO) in a syngeneic tumor system and its effect on tumor progression was investigated. Thus, anti-tumor reactive T cells were prepared in vivo by immunization of normal SJL/J mice with mitomycin C-inactivated tumor cells of the syngeneic transplantable reticulum cell sarcoma (RCS) line LA-6. Dividing cells were subsequently labeled by injecting iodo-2-deoxyuridine (¹²⁵IUdR) into the same animals 3 days later. Antigen-reactive cells (*ARC) present in the radiolabeled, nylon wool-fractionated spleen cell population taken from these mice on day 4 and injected IV into syngeneic SJL/J mice bearing LA-6 tumors were diverted to the liver and away from the spleen. The effect was maximal by 8 days following inoculation of tumor cells, and was specific inasmuch as ¹²⁵IUdR-labeled cells prepared by immunization with allogeneic spleen or tumor cells which were not opsonized in day-8 LA-6 tumor-bearing mice. Opsonization of *ARC in day-8 LA-6 tumor-bearing mice was completely abrogated by either prior injection of heat-aggregated immunoglobulin into the mice or preincubation of the *ARC in solubilized tumor antigen before injection into tumor-bearing mice, demonstrating the involvement of Fc receptors in the host and antigen-specific receptors on the *ARC, respectively, in the opsonizing process. When anti-LA-6 reactive T cells were incubated in serum from LA-6 tumor-bearing mice and then injected IV into normal syngeneic SJL/J mice, a similar liver diversion was observed. Serum from cyclophosphamide-pretreated mice injected with LA-6 or serum from mice given mitomycin C-inactivated LA-6 cells did not cause opsonization of tumor-reactive T cells, while a mixture of these two sera did have some *ARC opsonizing activity. Further experiments with SJL/J mice bearing spontaneous RCS tumor indicate that tumor-reactive T cells are also opsonized in these mice. The above studies and others suggested that ARCO may play an important role in vivo in the survival of tumors. Abbreviations used in this paper are: ARC, antigen-reactive cells; ARC, radiolabeled antigen-reactive cells; ARCO, antigen-reactive cell opsonization; LA-6 tumor line derived in our laboratory; L.I., localization index; PEG, polyethylene glycol; RCS, reticulum cell sarcoma; STA, soluble tumor antigen; TBS, tumor-bearer serum     

An age dependent decline in suppressor capacity of SJL/J mice.

Age dependent changes in immune regulation of SJL/J mice have been described by us, in terms of tolerance inducibility. We have now found evidence of the same type of change in the response to sheep erythrocytes. Thymus cells from young donors interfere in a reconstitution system with the plaque forming response of lymph node cells. This suppressive capacity disappears at the age of about 4 months and is gradually replaced by an enhancing effect of thymus cells. Similarly, low molecular suppressive factors are found in the serum of very young SJL/J mice and enhancing factors in the serum of older mice.     

Administration of dehydroepiandrosterone suppresses experimental allergic encephalomyelitis in SJL/J mice.

Experimental allergic encephalomyelitis (EAE) is a Th1-mediated inflammatory demyelinating disease in the CNS, an animal model of multiple sclerosis. We have examined the effect of dehydroepiandrosterone (DHEA) on the development of EAE in mice. The addition of DHEA to cultures of myelin basic protein-primed splenocytes resulted in a significant decrease in T cell proliferation and secretion of (pro)inflammatory cytokines (IFN-gamma, IL-12 p40, and TNF-alpha) and NO in response to myelin basic protein. These effects were associated with a decrease in activation and translocation of NF-kappaB. In vivo administration of DHEA significantly reduced the severity and incidence of acute EAE, along with a decrease in demyelination/inflammation and expressions of (pro)inflammatory cytokines in the CNS. These studies suggest that DHEA has potent anti-inflammatory properties, which at least are in part mediated by its inhibition of NF-kappaB activation.     

Induction of cell-mediated cytotoxic immunity to sperm-specific lactate dehydrogenase-C4 in SJL/J female mice

SJL/J female mice were tested for a cell-mediated cytotoxic response to sperm-specific lactate dehydrogenase C4 (LDH-C4). We demonstrated this response with a 51chromium release assay. Mouse LDH-C4 was coupled to EL-4 tumor cells. These cells were then labeled with 51Cr and mixed with splenocytes from LDH-C4-immune and -nonimmune mice. Specific lysis of the tumor cells by splenocytes from LDH-C4-immune mice was detected at 7 days and 14 days following a single footpad immunization. Since LDH-C4 is present on the surface of sperm, these results support the suggestion that cytotoxic removal of sperm from the female reproductive tract is one of the mechanisms whereby fertility is reduced following immunization with this enzyme.     

A novel class II-binding motif selects peptides that mediate organ-specific autoimmune disease in SWXJ,SJL/J,and SWR/J mice

Idiopathic dilated cardiomyopathy (DCM) is responsible for approximately 25% of all cases of congestive heart failure. We have recently shown that immunization of autoimmune-susceptible SWXJ mice with whole cardiac myosin leads to T cell-mediated experimental autoimmune myocarditis (EAMC) and DCM. We have now identified two disease-inducing peptides from cardiac alpha-myosin heavy chain (CAMHC). Our approach involved the use of a novel MHC class II-binding motif contained in several peptides known to be immunogenic in SWXJ (H-2(q,s)) mice or in the parental SJL/J (H-2(s)) or SWR/J (H-2(q)) mouse strains. Two of four CAMHC peptides containing the -KXXS- peptide motif were found to be immunogenic. Immunization of SWXJ or parental SJL/J and SWR/J mice with CAMHC peptides palpha406-425 or palpha1631-1650 resulted in EAMC and DCM, characterized by inflammation, fibrosis, and decompensated right-sided ventricular dilatation. Despite mediating high incidences of severe disease, both peptides were found to be cryptic determinants, thereby providing further evidence for the importance and perhaps predominance of self crypticity in autoimmunity. Both peptides showed dual parental I-A(q) and I-A(s) restriction and mediated passive transfer of disease with activated CD4(+) T cells. An intact motif was necessary for antigenicity because loss of activity occurred in peptides containing nonconservative substitutions at the motif's terminal lysine and serine residues. Our studies provide a new model for EAMC and DCM in strains of mice widely used in autoimmune studies. Moreover, the -KXXS- motif may be particularly useful in implicating previously overlooked proteins as autoimmune targets and in facilitating the development of new organ-specific autoimmune mouse models for human diseases.     

Role of the immune response in Sindbis virus-induced paralysis of SJL/J mice

The pathologic role of the specific immune and inflammatory responses to viral infections of the CNS was investigated by using mice which are susceptible (SJL/J) and resistant (C57Bl6 and BALB/c) to the development of experimental autoimmune encephalomyelitis (EAE). Intracerebral inoculation of 10(4) PFU of Sindbis virus (SV) into 6- to 8-wk-old SJL/J mice resulted in a severe and sometimes fatal encephalomyelitis. A mild to severe hind leg paralysis was observed around days 6 to 7 postinfection (pi) which closely resembled EAE stages and persisted for up to 8 wk pi. Immunosuppression with cyclophosphamide on day 4 alleviated the severity of this disease. Significant perivascular and parenchymal infiltration was present in the brains and spinal cords of SV-infected SJL/J mice for up to 1 mo. This apparent immunopathologic reaction was found to be a characteristic of SJL/J mice, because infection of 6- to 8-wk-old BALB/c and C57Bl6 mice with SV did not cause paralytic disease. These mice also exhibited a significantly milder cellular infiltrate which was mostly resolved on day 12 to 14 pi. Titers of virus in the brain and spinal cords of mice were comparable with clearance by day 7 pi. SV-specific lymphoproliferation and serum antibody responses were also comparable in all mice. SV-infected SJL/J mice developed antibodies to myelin components as demonstrated in Western blots and responded to myelin basic protein by lymphoproliferation. Lymph node cells from these mice, after in vitro challenge with myelin basic protein, transferred a mild EAE-like disease to naive recipients and potentiated subclinical EAE into a severe disease.     

Characterization of the molecules on SJL/J lymphomas which stimulate syngeneic T cells

I-A antigens isolated from SJL reticulum cell sarcoma (RCS) cells show greater heterogeneity with respect to charge and size of the A alpha chains than do I-A antigens isolated from normal SJL spleen cells. The relevance of these structural changes in RCS I-A to the previously shown syngeneic T cell stimulatory properties of RCS was investigated. It was shown that RCS cells expressed acidic forms of the A alpha chain on their cell surface which were not present on SJL spleen cells, peritoneal cells, or dendritic cells. The only normal cells which showed A alpha chain heterogeneity approaching that of RCS cells were LPS-induced B cell blasts. Treatment with tunicamycin completely abolished the RCS A alpha chain heterogeneity, whereas exposure to neuraminidase removed the charge heterogeneity, but not the size heterogeneity. Parallel studies of the syngeneic T cell proliferative response to RCS showed that tunicamycin abolished, while neuraminidase enhanced, the ability of RCS cells to stimulate syngeneic T cells. It is suggested that polysaccharide chains on RCS I-A molecules are particularly important for the biologic properties of these lymphoma cells. The possibility that highly glycosylated I-A antigens on normal B cell blasts are also involved in the stimulation of syngeneic T cells is discussed.     

T-helper-cell-specific monoclonal antibody inhibits growth of B-cell lymphomas in syngeneic SJL/J mice

Transplantable follicular center cell lymphomas of SJL/J mice are B-cell tumors that stimulate proliferation of host T-helper (TH) cells and which grow progressively in the peripheral lymphoid tissues of immunocompetent recipients. However, tumor growth is compromised in immunosuppressed syngeneic recipients, suggesting that the host response to SJL follicular center cell (SJL/FCC) lymphoma cells is required for optimal tumor growth. In vitro studies indicate that the host TH cells (Lyt-1+, 2-, L3T4a+) which respond to the major histocompatibility complex (MHC) class II (I-As) surface determinants on the SJL/FCC lymphoma cells produce a variety of lymphokines, some of which may promote tumor growth in vivo. The results of this study demonstrate that treatment of lymphoma-injected mice with L3T4a-specific mAb inhibits the growth of the SJL/FCC lymphoma cells, despite the fact that these tumor cells do not express L3T4a determinants. Thus, in this model, mAb therapy targeting host immune cells rather than the tumor cells is an effective means to control tumor growth. Long-term observation of SJL/FCC lymphoma-injected, anti-L3T4a mAb-treated mice reveals prolonged survival of the majority of these animals with periodic recurrence of tumor growth. During periods of remission, LN cells from these long-term surviving animals were unable to mount the characteristic in vitro host response to irradiated SJL/FCC lymphoma cells. These results provide direct evidence that SJL/FCC lymphoma cells fail to retain their characteristic neoplastic properties in a microenvironment that is initially devoid of tumor-responsive TH cells.     

Adoptively transferred experimental autoimmune encephalomyelitis in SJL/J, PL/J, and (SJL/J x PL/J)F1 mice. Influence of I-A haplotype on encephalitogenic epitope of myelin basic protein

Guinea pig basic protein (GPBP)-immune lymph node cells (LNC) from SJL, PL, and SJL x PL (F1) mice proliferated to whole GPBP and GPBP fragments 1-37, 43-88, and 89-169. All three strains of mice developed experimental allergic encephalomyelitis (EAE) by active immunization with whole GPBP or by passive transfer of LNC cultured with whole GPBP. SJL (H-2s) and PL (H-2u) mice developed EAE by active immunization with fragments 89-169 or 1-37, respectively, or by passive transfer of LNC cultured with the same Ag. F1 mice developed EAE by active immunization only with fragment 1-37 or by passive transfer of LNC cultured with either of the above fragments. Removal of macrophages (MO) from immune-F1 LNC resulted in the loss of a proliferative response and the ability to transfer EAE. Reconstitution of MO-depleted immune F1 T cells with either F1-, SJL-, or PL-MO restored the proliferative responses to whole GPBP and the three fragments. Cultures of immune F1 T cells reconstituted with any of the three MO populations and incubated with whole GPBP passively transferred EAE into naive F1 mice. Immune F1 T cells cultured with F1 MO in the presence of either fragment 1-37 or 89-169 transferred EAE. F1 T cells cultured with SJL MO were able to transfer EAE only if the Ag was fragment 89-169, whereas F1 T cells cultured with PL MO were able to transfer disease only if incubated in the presence of fragment 1-37. F1 mice are passively susceptible to EAE induced by adoptive transfer of cells reactive to either the N-terminal or C-terminal fragment and that the encephalitogenic determinant of GPBP is related to the genome of MO present in vitro.     

Quantitative trait loci that harbor genes regulating muscle size in (MRL/MPJ x SJL/J) F(2) mice

The genetic mechanisms that determine muscle size have not been elucidated, even though it is a key musculoskeletal parameter that reflects muscle strength. In this study, we performed a high-density genome-wide scan using 633 (MRL/MPJ × SJL/J) F₂ intercross 7-week-old mice to identify quantitative trait loci (QTL) involved in the determination of muscle size. Significant QTL were identified for muscle size and body length. Muscle size (adjusted by body length) QTL were identified on chromosomes 7, 9, 11, 14 (two QTL) and 17, which together explained 19.2% of phenotypic variance in F₂ mice, while body length QTL were located on chromosome 2 (two QTL), 9, 11 and 17 which accounted for 28.3% of phenotypic variance in F₂ mice. Three significant epistatic interactions between different QTL positions from muscle size and body length were identified (P <0.01) on chromosomes 2, 9, 14 and 17, which explained 16.1% of the variance in F₂ mice. Electronic Publication     

Murine resistance to street rabies virus: genetic analysis by testing second-backcross progeny and verification of allelic resistance genes in SJL/J and CBA/J mice

Intraperitoneal challenge with street rabies virus of second-backcross offspring produced from susceptible females mated with either randomly selected or rabies-resistant first-backcross males indicated that murine resistance is under the influence of the concurrent presence of each of two segregating genes. Furthermore, the greater than or equal to 96% resistance of offspring produced from (SJL X CBA)F1 and (CBA X SJL)F1 hybrids crossed to susceptible A.SW or A/WySn mice demonstrated that resistance genes of SJL/J and CBA/J mice are allelic.     

The genotype of bone marrow-derived inflammatory cells does not account for differences in skeletal muscle regeneration between SJL/J and BALB/c mice

This study determined whether the genotype of bone marrow-derived inflammatory cells contributes to the more pronounced leukocytic exudation and extensive new muscle formation seen in SJL/J compared with BALB/c mice after a crush-injury (Mitchell et al. 1992). Female SJL/J mice were whole-body irradiated and reconstituted with male bone marrow from the BALB/c strain, and irradiated BALB/c females reconstituted with male SJL/J bone marrow. The mice were allowed to recover for 3 weeks and the tibialis anterior muscle (in a leg which had been protected from irradiation) was injured by crushing. At 3 and 10 days after injury the extent of necrotic debris, mononuclear leukocytic infiltration and new muscle formation was assessed in the muscles. The SJL/J mice reconstituted with BALB/c bone marrow showed extensive mononuclear leukocytic infiltration and clearance of necrotic debris when compared with BALB/c mice reconstituted with SJL/J bone marrow, and these strain-specific differences mirrored those seen with control bone marrow reconstituted hosts and non-irradiated hosts. The results show that the genotype of the bone marrow-derived macrophages is not responsible for the superior regeneration of crush-injured skeletal muscle in SJL/J mice, and it appears that factors intrinsic to the muscle tissue may be of central importance.     

Effects of FVB/NJ and C57Bl/6J strain backgrounds on mammary tumor phenotype in inducible nitric oxide synthase deficient mice

The ability to genetically manipulate mice has led to rapid progress in our understanding of the roles of different gene products in human disease. Transgenic mice have often been created in the FVB/NJ (FVB) strain due to its high fecundity, while gene-targeted mice have been developed in the 129/SvJ-C57Bl/6J strains due to the capacity of 129/SvJ embryonic stem cells to facilitate germline transmission. Gene-targeted mice are commonly backcrossed into the C57Bl/6J (B6) background for comparison with existing data. Genetic modifiers have been shown to modulate mammary tumor latency in mouse models of breast cancer and it is commonly known that the FVB strain is susceptible to mammary tumors while the B6 strain is more resistant. Since gene-targeted mice in the B6 background are frequently bred into the polyomavirus middle T (PyMT) mouse model of breast cancer in the FVB strain, we have sought to understand the impact of the different genetic backgrounds on the resulting phenotype. We bred mice deficient in the inducible nitric oxide synthase (iNOS) until they were congenic in the PyMT model in the FVB and B6 strains. Our results reveal that the large difference in mean tumor latencies in the two backgrounds of 53 and 92 days respectively affect the ability to discern smaller differences in latency due to the Nos2 genetic mutation. Furthermore, the longer latency in the B6 strain enables a more detailed analysis of tumor formation indicating that individual tumor development is not stoichastic, but is initiated in the #1 glands and proceeds in early and late phases. NO production affects tumors that develop early suggesting an association of iNOS-induced NO with a more aggressive tumor phenotype, consistent with human clinical data positively correlating iNOS expression with breast cancer progression. An examination of lung metastases, which are significantly reduced in PyMT/iNOS^−/− mice compared with PyMT/iNOS^+/+ mice only in the B6 background, is concordant with these findings. Our data suggest that PyMT in the B6 background provides a useful model for the study of inflammation-induced breast cancer.     

Natural killer cell activity in reticulum cell sarcomas (RCS) of SJL/J mice.

Two transplantable reticulum cell sarcomas (RCS) of SJL mice expressed marked levels of natural killer (NK) activity when tested against susceptible ⁵¹Cr-labeled tumor targets. In contrast, normal SJL lymph node and spleen cells demonstrated low levels of NK activity. Neither depletion of macrophages nor pretreatment with anti-Thy-1.2 sera and complement reduced the capacity of RCS cells to express NK activity. Systemic injection of irradiated RCS cells into SJL mice induced a transient increase in NK activity at 3 and 7 days after injection. However, the NK activity observed in recipients of irradiated RCS cells never reached levels comparable to those of control mice injected with viable tumor cells. These data suggest that the transplantable reticulum cell sarcomas of SJL mice may represent a tumor of natural killer cells and thus provide an enriched source of these effectors that may be useful for further characterization of natural cytotoxicity.     

Sodium phenylacetate inhibits adoptive transfer of experimental allergic encephalomyelitis in SJL/J mice at multiple steps

Experimental allergic encephalomyelitis (EAE) is the animal model for multiple sclerosis. The present study underlines the importance of sodium phenylacetate (NaPA), a drug approved for urea cycle disorders, in inhibiting the disease process of adoptively transferred EAE in female SJL/J mice at multiple steps. Myelin basic protein (MBP)-primed T cells alone induced the expression of NO synthase (iNOS) and the activation of NF-kappaB in mouse microglial cells through cell-cell contact. However, pretreatment of MBP-primed T cells with NaPA markedly inhibited its ability to induce microglial expression of iNOS and activation of NF-kappaB. Consistently, adoptive transfer of MBP-primed T cells, but not that of NaPA-pretreated MBP-primed T cells, induced the clinical symptoms of EAE in female SJL/J mice. Furthermore, MBP-primed T cells isolated from NaPA-treated donor mice were also less efficient than MBP-primed T cells isolated from normal donor mice in inducing iNOS in microglial cells and transferring EAE to recipient mice. Interestingly, clinical symptoms of EAE were much less in mice receiving NaPA through drinking water than those without NaPA. Similar to NaPA, sodium phenylbutyrate, a chemically synthesized precursor of NaPA, also inhibited the disease process of EAE. Histological and immunocytochemical analysis showed that NaPA inhibited EAE-induced spinal cord mononuclear cell invasion and normalized iNOS, nitrotyrosine, and p65 (the RelA subunit of NF-kappaB) expression within the spinal cord. Taken together, our results raise the possibility that NaPA or sodium phenylbutyrate taken through drinking water or milk may reduce the observed neuroinflammation and disease process in multiple sclerosis patients.     

Glutathione deficient C57BL/6J mice are not sensitized to ozone-induced lung injury

In this study we examined the role of the antioxidant glutathione (GSH) in pulmonary susceptibility to ozone toxicity, utilizing GSH deficient C57BL/6J mice that lack the expression of glutamate-cysteine ligase modifier subunit (GCLM). Gclm(−/−) knockout mice had 70% GSH depletion in the lung. Gclm(+/+) wild-type and Gclm(−/−) mice were exposed to either 0.3 ppm ozone or filtered air for 48 h. Ozone-induced lung hyperpermeability, as measured by total protein concentration in bronchoalveolar lavage fluid, was surprisingly lower in Gclm(−/−) mice than in wild-type mice. Lung hyperpermeability did not correlate with the degree of neutrophilia or with inflammatory gene expression. Pulmonary antioxidant response to ozone, assessed by increased mRNA levels of metallothionein 1 and 2, α-tocopherol transporter protein, and solute carrier family 23 member 2 (sodium-dependent vitamin C transporter) was greater in Gclm(−/−) mice than in Gclm(+/+) mice. These results suggest that compensatory augmentation of antioxidant defenses in Gclm(−/−) mice may confer increased resistance to ozone-induced lung injury.