Effects of non-MHC loci on resistance to retrovirus-induced immunodeficiency in mice

Transformation of (sup14)C-Lignin-Labeled Cell Walls of Wheat by Syntrophococcus sucromutans, Eubacterium oxidoreducens, and Neocallimastix frontalis

Wheat cell walls, saponified or not, labeled with [U-(sup14)C]phenylalanine or [O-methyl-(sup14)C]sinapate were fermented by Neocallimastix frontalis or Syntrophococcus sucromutans plus Eubacterium oxidoreducens or a mixed culture. Phenolics were less solubilized but more transformed by bacteria than by the fungus, and mineralization was slight. S. sucromutans O-demethylated [O-methyl-(sup14)C]syringyl lignins, yielding labeled acetate.

alpha-Glucuronidase and Other Hemicellulase Activities of Fibrobacter succinogenes S85 Grown on Crystalline Cellulose or Ball-Milled Barley Straw

Fibrobacter succinogenes produces an alpha-glucuronidase which cleaves 4-O-methyl-alpha-d-glucuronic acid from birch wood 4-O-methyl-alpha-d-glucuronoxylan. Very low levels of alpha-glucuronidase activity were detected in extracellular enzyme preparations of F. succinogenes on birch wood xylan substrate. The release of 4-O-methyl-alpha-d-glucuronic acid was enhanced when the birch wood xylan substrate was predigested by either a purified Schizophyllum commune xylanase or a cloned F. succinogenes S85 xylanase. These data suggest that the alpha-glucuronidase is unable to cleave 4-O-methyl-alpha-d-glucuronic acid from intact xylan but can act on unique low-molecular-weight glucuronoxylan fragments created by the cloned F. succinogenes xylanase. The cloned xylanase presumably must account for a small proportion of the indigenous xylanase activity of F. succinogenes cultures, since this xylanase source does not support high glucuronidase activity. The alpha-glucuronidase and associated hemicellulolytic enzymes exhibited higher activities in culture fluid from cells grown on ball-milled barley straw than in that of cellulose-grown cells. The profile of xylanases separated by isoelectric focusing (zymogram) of culture filtrate from cells grown on barley straw was more complex than that of culture filtrates from cells grown on cellulose. These data demonstrate that F. succinogenes produces an alpha-glucuronidase with an exacting substrate specificity which enables extensive cleavage of glucuronic acid residues from xylan as a consequence of synergistic xylanase action.

Degradation of Perennial Ryegrass Leaf and Stem Cell Walls by the Anaerobic Fungus Neocallimastix sp. Strain CS3b

The degradation of cell walls isolated from stems and leaves of perennial ryegrass by the anaerobic fungus Neocallimastix sp. strain CS3b was studied in a defined medium. The combined cellulose and hemicellulose fraction represented 53.1 (wt/wt) and 63.3% (wt/wt) of the dry weight of control grass leaf and stem cell walls, respectively. In both leaf and stem cell walls, glucose was the major neutral monosaccharide, followed by xylose, arabinose, and galactose. After 2 days of fermentation with Neocallimastix sp. strain CS3b, treated cell walls contained smaller amounts of neutral sugars compared with those of undigested cell walls. These results were more evident for glucose, xylose, and arabinose than for galactose. Furthermore, the sugar content of leaf cell walls decreased before a decline in the sugar content of stem cell walls was observed. Data from formate and hydrogen production indicated that the growth of Neocallimastix sp. strain CS3b was completed in 4 days in the culture system used. During this period, the fungus liberated about 95% of the fermentable sugars in untreated material. On a percentage basis, no significant differences were found in final extent of degradation of glucose, xylose, and arabinose. Galactose, however, was degraded to a lesser extent.

Anti-Gag cytolytic T lymphocytes specific for an alternative translational reading frame-derived epitope and resistance versus susceptibility to retrovirus-induced murine AIDS in F(1) mice

Murine AIDS (MAIDS) develops in susceptible mouse strains after infection with the LP-BM5 murine leukemia virus complex that contains causative defective, and ecotropic helper, retroviruses. We previously demonstrated that the MAIDS-resistant H-2(d) strains BALB/cByJ and C57BL/KsJ generate MHC class I (K(d)) restricted virus-specific CD8(+) cytolytic T lymphocytes (CTLs) that lyse cells expressing either defective or ecotropic gag proteins. In contrast, the congenic BALB.B and closely related C57BL/6J MAIDS-susceptible H-2(b) strains were unable to serve as a source of gag-specific CTLs (Schwarz and Green, 1994), suggesting that anti-gag CTLs might provide a basis for resistance to MAIDS. Although its susceptibility to MAIDS was unknown, the (BALB/c x C57BL/6J) F(1) (CBY6F(1)) strain could also produce H-2(d)-, but not H-2(b)-, restricted, anti-gag CTLs (Schwarz and Green, 1994). Because of this correlation between anti-gag CTLs and resistance to MAIDS, it was important to provide more direct evidence in support of CTL-mediated protection and to determine both the fine specificity of CByB6F(1) anti-gag CTLs, in comparison with the resistant C57BL/Ks and BALB/c strains, and the susceptibility of this F(1) strain to LP-BM5-induced MAIDS. We report here that no symptoms of MAIDS were observed in CBY6F(1) (H-2(dxb)) mice. For F(2) mice, in contrast to the high susceptibility of H-2(b/b) mice, 77% of H-2(d/d) and 81% of H-2(b/d) F(2) mice did not exhibit MAIDS after LP-BM5 infection. These results are in contrast to other published studies that concluded that susceptibility, rather than resistance, is dominant in F(1) (resistant x susceptible or susceptible x resistant) mice. We also show that CBY6F(1) anti-gag CTLs exhibit a fine specificity shared by the MAIDS-resistant BALB/c and C57BL/Ks strains, that is, the immunodominant gag epitope, SYNTGRFPPL, encoded by an alternative open reading frame. Together with our direct demonstration here that in vivo monoclonal antibody (mAb) depletion of CD8(+) T cells converts genetically resistant mice to MAIDS susceptibility, these data on the ability to mount anti-ORF2/SYNTGRFPPL, gag-specific CTL responses strongly suggest that CTLs are a primary factor in determining MAIDS resistance. Accordingly, given the K(d)-restricted nature of the CTLs, the main genetic determinant of resistance appeared to be the codominant expression of the resistant H-2(d) haplotype. Interestingly, however, 19% of H-2(d/b) and 23% of the H-2(d/d) F(2) mice had at least one clinical aspect of MAIDS, suggesting that a non-MHC genetic determinant(s) can negatively influence T-cell protection and thus disease outcome

Relationship of cytokines and cytokine signaling to immunodeficiency disorders in the mouse

The contributions of cytokines to the development and progression of disease in a mouse model of retrovirus-induced immunodeficiency (MAIDS) are controversial. Some studies have indicated at etiologic role for type 2 cytokines, while others have emphasized the importance of type 1 cytokines. We have used mice deficient in expression of IL-4, IL-10, IL-4 and IL-10, IFN-gamma, or ICSBP-a transcriptional protein involved in IFN signaling-to examine their contributions to this disorder. Our results demonstrate that expression of type 2 cytokines is an epiphenomenon of infection and that IFN-gamma is a driving force in disease progression. In addition, exogenously administered IL-12 prevents many manifestations of disease while blocking retrovirus expression. Interruption of the IFN signaling pathways in ICSBP-/- mice blocks induction of MAIDS. Predictably, ICSBP-deficient mice exhibit impaired responses to challenge with several other viruses. This immunodeficiency is associated with impaired production of IFN-gamma and IL-12. Unexpectedly, however, the ICSBP-/- mice also develop a syndrome with many similarities to chronic myelogenous leukemia in humans. The chronic phase of this disease is followed by a fatal blast crisis characterized by clonal expansions of undifferentiated cells. ICSBP is thus an important determinant of hematopoietic growth and differentiation as well as a prominent signaling molecule for IFNs.

Control of immunodeficiency and lymphoproliferation in mouse AIDS: studies of mice deficient in CD8+ T cells or perforin

CD8+ T cells were previously shown to be important in preventing lymphoproliferation and immunodeficiency following infection of murine AIDS (MAIDS)-resistant mice with the LP-BM5 mixture of murine leukemia viruses. To further evaluate the mechanisms contributing to MAIDS resistance, we studied mice lacking CD8+ T cells or deficient in perforin due to knockout of the beta2-microglobulin (beta2M) or perforin gene, respectively. In contrast to wild-type, MAIDS-resistant controls, B10.A mice homozygous for the beta2M mutation and B10.D2 mice homozygous for the perforin mutation were diagnosed as having MAIDS by 5 to 8 weeks after infection by the criteria of lymphoproliferation, impaired proliferative responses to mitogens, and changes in cell populations as judged by histopathology and flow cytometry. Unexpectedly, there was no progression of lymphoproliferation through 24 weeks, even though immune functions were severely compromised. Expression of the defective virus responsible for MAIDS was enhanced in spleens of the knockouts in comparison with wild-type mice. These results demonstrate that perforin-dependent functions of CD8+ T cells contribute to MAIDS resistance but that other, non-CD8-dependent mechanisms are of equal or greater importance.

Recovery from retrovirus-induced immune suppression in BDP/J mice: dominance of the "regressor' phenotype

Murine acquired immune deficiency syndrome (MAIDS) is an immunosuppressive disease of mice induced by infection with the LP-BM5 murine leukemia virus (MuLV) retrovirus isolate. Certain inbred strains of mice are resistant to disease, but F1 crosses between sensitive and resistant strains are predominantly sensitive to MAIDS. One inbred strain, BDP, demonstrates a novel disease phenotype, recovery of immune function after a period of profound immune suppression. This trait is genetically dominant in crosses between BDP and either sensitive or resistant strains. The 'regressor' phenotype reveals the existence of a mechanism for recovery from immunosuppressive retrovirus infections, which may be of import in developing therapies for AIDS patients.

Alpha/beta interferons increase host resistance to murine AIDS

Murine AIDS (MAIDS) is caused by a defective retrovirus present in the LP-BM5 murine leukemia virus mixture. Strains of inbred mice differ in resistance to MAIDS development; some are susceptible (e.g., C57BL/6), while others are resistant (e.g., CBA and B10.BR). As an early block to viral replication in resistant mice has been demonstrated previously by PCR studies, we postulated that alpha/beta interferons (IFN-alpha/beta) may be involved in resistance to MAIDS. Susceptible C57BL/6 mice infected with LP-BM5 were treated with IFN-alpha/beta or Newcastle disease virus. Newcastle disease virus induces high endogenous IFN-alpha/beta production in mice. Both treatments delayed the development of MAIDS, as assessed by splenomegaly and T- and B-cell proliferation. In addition, an IFN-alpha/beta response was detected by reverse transcription-PCR and dot blotting 3, 6, and 9 h after LP-BM5 infection in resistant mice but not in susceptible mice. These results suggest that the ability to produce IFN-alpha/beta in response to LP-BM5 infection may contribute to host resistance to MAIDS.

Retrovirus-induced lymphoproliferative disease in mice undergoing graft-versus-host reaction

The effect of graft-versus-host reaction on the course of concommitant retrovirus-induced lymphoproliferative disease was investigated. The graft-versus-host reaction was elicited by a single i.v. injection of 1.2 x 10(8) parental spleen cells into adult F1 mice. Lymphoproliferative disease was induced by a single transfusion of 0.2 ml of whole blood from donors with fully developed disease, induced by infection with retrovirus LP-BM5 MuLV. Graft-versus-host reaction and the lymphoproliferative disease each separately produced similar syndrome consisting of splenomegaly, lymphadenopathy, leukopenia, neutrophilia, reduced in vitro proliferation of spleen cells and suppression of in vivo immune responsiveness. The above symptoms were usually less pronounced during graft-versus-host reaction. Ongoing graft-versus-host reaction neither aggravated nor accelerated the course of the virus-induced lymphoproliferative disease in genetically susceptible F1 hybrids. Likewise, an ongoing graft-versus-host reaction in genetically resistant F1 hybrids did not alter their susceptibility to the retrovirus infection. The apparent lack of the effect of graft-versus-host reaction -dependent immunosuppression on the severity and the course of the concommitant retrovirus-induced lymphoproliferative disease suggests pathogenic differences between the murine syndrome and human AIDS for which the murine disease is considered by some to be an animal model.

Retrovirus-induced lymphoproliferative disease in mice: role of humoral immunity in perinatally exposed mice

The mice born to female mice infected with LP-BM5 MuLV, the etiologic agent for lymphoproliferative disease and nursed for 4-6 weeks by them were less susceptible upon reinfection by i.v. transfusion of blood or plasma from infected donors with fully developed disease. Sera of 7 week or older perinatally exposed mice were capable of a complete in vitro neutralization of virus in plasma or blood from mice with fully developed disease. In contrast, sera from 3-week old perinatally exposed mice were ineffective. The neutralizing ability of the sera was drastically reduced or abrogated after their absorption with anti-mouse IgM. These observations are consistent with the notion that perinatally exposure results ina moderate form of the disease of the offspring. This perinatal infection is followed by a production of neutralizing antibodies of predominantly the IgM class that significantly alters the course of the lymphoproliferative disease and, in some instances, even prevents its development.

Impact of MHC class I gene on resistance to murine AIDS

Development of murine AIDS in mice following infection with LP-BM5 murine leukaemia virus (MuLV) is highly strain dependent, with strain differences determined by genes within and outside H-2. Among H-2 genes, the Dd gene is the most closely associated with resistance to LP-BM5 MuLV infection. However, the Dd-mediated resistance is highly influenced by outside H-2 genes, i.e. A lineage strains are more resistant than mice strains of B6/B10 lineage. In this study, the mice having BALB background were analysed and, similarly to A lineage mice, only Dd gene products were found to be required to provide resistance to LP-BM5 MuLV infection. Furthermore, BALB/c Kh mice bearing both Dd and Ld genes clearly showed obviously higher resistance than BALB/c-H-2dm2 mice solely having the Dd gene. In addition, in the long-term observation of the effect of the Dd gene on B6/B10 background mice, D8 mice having the Dd gene as a transgene and expressing a high level Dd gene product showed higher resistance than naturally recombinant B10.A(18R) mice. These results suggest that the MAIDS resistance associated with the D end loci is dependent on the level of expression of an MHC class I gene.

Acquired immunodeficiency in murine lymphoproliferative disease: considerations on pathogenesis

C57BL/6Kh mice were infected with a single i.p. injection of 1 x 10(5) FFU of LP-BM5 MuLV. The development and progress of the virus-induced lymphoproliferative disease was followed for 12 weeks after infection. As anticipated, progressive splenomegaly and lymphadenopathy, as well as almost total abrogation of immune responsiveness ensued. In contrast to previous reports, there was a dramatic increase in the frequency of CD4+ cells in spleens among which over 20% expressed V beta 5 TCR, as compared with fewer than 3% in spleens of normal mice. Spleen cells from infected mice retained their in vitro ability to proliferate upon stimulation with IL-2 and anti-CD3, but were unable to respond when stimulated with phorbol ester and either a low dose of IL-2 or calcium ionophore (ionomycin). A similar pattern of in vitro proliferative responses was obtained when normal spleen cells were treated with K252a compound, a known inhibitor of protein kinase C activity. Together with the observations that viral infection impaired down-regulation of the phorbol-induced kinase activity and that the kinase inhibitor only marginally enhanced suppression of virus-infected cells proliferation, this finding suggests that disturbances of protein kinase C activity may underly the pathological effects seen after viral infection. However, since no apparent quantitative and qualitative changes in protein kinase C itself and its translocation were observed, it is more likely that the virus may interfere with either the substrate or product of kinase activity.

Resistance of mice deficient in IL-4 to retrovirus-induced immunodeficiency syndrome (MAIDS)

The murine acquired immunodeficiency syndrome (MAIDS) is induced by a defective murine leukemia virus and has many symptoms similar to those found in patients infected with the human immunodeficiency virus. The presence of both B cells and CD4+ T cells is critical for the development of the disease. Furthermore, a Th2 cytokine response dominates during the progression of the disease. When interleukin-4 (IL-4)-deficient mice that are defective in Th2 cytokine responses were infected, there was no lethality, and the development of the T cell abnormalities associated with MAIDS was delayed. These data suggest that IL-4 or a Th2 response is involved in the development of retrovirus-induced immunodeficiency in mice.

Experimental murine paracoccidioidomycosis: relationship among the dissemination of the infection, humoral and cellular immune responses

The dissemination of Paracoccidioides brasiliensis cells to the heart, omentum/pancreas, spleen, liver and lungs, assessed by colony forming unit (CFU) counts, the levels of specific antibodies to this fungal agent (by ELISA), and the specific DTH reaction were studied in susceptible (B10.A) and resistant (A/Sn) mice. The animals were infected intraperitoneally with P. brasiliensis yeast cells and were evaluated 2, 4, 12 and 16 weeks later. The most remarkable differences between the two mouse strains were observed 16 weeks after infection, when B10.A mice displayed high numbers of CFU in all examined organs, except the heart, high antibody titres, and depressed DTH response. At this point, A/Sn mice presented low or absent CFU in all organs, low antibody titres and expressive DTH response. The CFU counts were shown to be a reliable parameter to discriminate susceptible from resistant animals. The fungal load in the most affected organs correlated with the antibody titres and was inversely correlated with the intensity of the DTH reaction. The patterns of immune response in this model mimic human paracoccidioidomycosis, in which high specific antibody levels and depressed DTH reactions are found in multifocal and severe forms of the disease.

The MA (p15) and p12 regions of the gag gene are sufficient for the pathogenicity of the murine AIDS virus

Inoculation of the replication-defective retrovirus DEF27 (BM5d), packaged as an amphotropic virus pseudotype, into C57BL/6J mice leads to development of murine AIDS. Disease development showed a long incubation period (20 to 24 weeks), was associated with amplification of the BM5d provirus in splenocytes and lymph nodes, and was independent of the presence of exogenous or endogenous replication-competent helper viruses. However, both the onset of disease and amplification of the defective provirus were significantly enhanced by coinfection with the replication-competent B-cell-tropic ecotropic helper virus BM5e. The part of the BM5d viral genome that was essential for the pathogenicity was determined by making precisely engineered alterations in the reading frame of the gag and pol genes of BM5d proviral DNA and examining the ability of the altered amphotropic BM5d pseudotypes to induce the disease in C57BL/6J mice. The results show that expression of the MA (p15) and p12 regions of the gag gene is sufficient for pathogenicity of the BM5d retrovirus.

A modular esterase from Pseudomonas fluorescens subsp. cellulosa contains a non-catalytic cellulose-binding domain

The 5' regions of genes xynB and xynC, coding for a xylanase and arabinofuranosidase respectively, are identical and are reiterated four times within the Pseudomonas fluorescens subsp. cellulosa genome. To isolate further copies of the reiterated xynB/C 5' region, a genomic library of Ps. fluorescens subsp. cellulosa DNA was screened with a probe constructed from the conserved region of xynB. DNA from one phage which hybridized to the probe, but not to sequences upstream or downstream of the reiterated xynB/C locus, was subcloned into pMTL22p to construct pFG1. The recombinant plasmid expressed a protein in Escherichia coli, designated esterase XYLD, of M(r) 58,500 which bound to cellulose but not to xylan. XYLD hydrolysed aryl esters, released acetate groups from acetylxylan and liberated 4-hydroxy-3-methoxycinnamic acid from destarched wheat bran. The nucleotide sequence of the XYLD-encoding gene, xynD, revealed an open reading frame of 1752 bp which directed the synthesis of a protein of M(r) 60,589. The 5' 817 bp of xynD and the amino acid sequence between residues 37 and 311 of XYLD were almost identical with the corresponding regions of xynB and xynC and their encoded proteins XYLB and XYLC. Truncated derivatives of XYLD lacking the N-terminal conserved sequence retained the capacity to hydrolyse ester linkages, but did not bind cellulose. Expression of truncated derivatives of xynD, comprising the 5' 817 bp sequence, encoded a non-catalytic polypeptide that bound cellulose. These data indicate that XYLD has a modular structure comprising of a N-terminal cellulose-binding domain and a C-terminal catalytic domain.

Dissociation between lymphoproliferative responses and virus replication in mice with different sensitivities to retrovirus-induced immunodeficiency

Murine AIDS (MAIDS) is induced by a replication-defective virus (BM5d). In susceptible mice (C57BL/6J), inoculation with LP-BM5 murine leukemia virus, which consists of the BM5d virus and replication-competent B-tropic ecotropic (BM5e) and milk cell focus-inducing (BM5-MCF) helper viruses results in the polyclonal proliferation of T and B cells, immunodeficiency, and the expansion of B cells containing the BM5d provirus followed by the development of B-cell lymphomas. Several strains of mice that are resistant to LP-BM5-induced murine AIDS have been identified, and major histocompatibility complex genes as well as non-major histocompatibility complex genes were shown to play a role in this resistance. In the present study, we have examined and compared the replication of the BM5d and BM5e viruses after inoculation of LP-BM5 into sensitive (C57BL/6J) and resistant (C57BL/KSJ) mice. Using a specific polymerase chain reaction, we could detect the BM5d and BM5e proviruses as early as 1 week postinfection in the sensitive mice, and the levels of both viruses increased significantly with the progression of the disease. In contrast, in the resistant C57BL/KSJ mice, replication of BM5d and BM5e was restricted and no BM5d and only very low levels of the BM5e provirus could be detected either at early or late times postinoculation with the LP-BM5 virus mixture. Inoculation with LP-BM5 did not lead to the production of antibodies that could recognize the BM5d-encoded Pr60gag in either the sensitive or resistant mice; however, production of antibodies recognizing the env-related proteins of the helper virus was detected in the resistant but not in the sensitive mice at late times postinfection. Interestingly, inoculation with LP-BM5 increased polyclonal stimulation of spleen cells and decreased mitogen stimulation in both strains of mice. This stimulation of splenocytes persisted in the sensitive mice but decreased after a few weeks in the resistant mice. These results show an early block in BM5d and BM5e replication in the resistant C57BL/KSJ mice and indicate that resistance is a consequence of the inhibition of an onset of the BM5d virus infection and its expansion. However, initial responses to virus infection such as proliferation of spleen cells and response to mitogen are similar in both strains of mice and are therefore not necessarily related to the development of the disease.