Toxoplasma gondii infection blocks the development of allergic airway inflammation in BALB/c mice.

There is a link between increased allergy and a reduction of some infections in western countries. Epidemiological data also show that respiratory allergy is less frequent in people exposed to orofaecal and foodborne microbes such as Toxoplasma gondii. Infection with T. gondii induces a strong cell-mediated immunity with a highly polarized T helper type 1 (Th1) response in early stages of infection. Using a well-known murine model of allergic lung inflammation, we sought to investigate whether T. gondii infection could modulate the susceptibility to develop respiratory allergies. Both acute and chronic infection with T. gondii before allergic sensitization resulted in a diminished allergic inflammation, as shown by a decrease in bronchoalveolar lavage (BAL) eosinophilia, mononuclear and eosinophil cell infiltration around airways and vessels and goblet cell hyperplasia. Low allergen-specific immunoglobulin (Ig)E and IgG1 and high levels of allergen-specific IgG2a serum antibodies were detected. A decreased interleukin (IL)-4 and IL-5 production by lymph node cells was observed, while no antigen-specific interferon-gamma increase was detected. Higher levels of the regulatory cytokine IL-10 were found in BAL from infected mice. These results show that both acute and chronic parasite infection substantially blocked development of airway inflammation in adult BALB/c mice. Our results support the hypothesis that T. gondii infection contributes to protection against allergy in humans.

Differential susceptibility to acute Trypanosoma cruzi infection in BALB/c and C57BL/6 mice is not associated with a distinct parasite load but cytokine abnormalities.

Inoculation of Trypanosoma cruzi, Tulahuén strain, into C57BL/6 and BALB/c mice led to an acute infection characterized by marked parasitaemia, myocardial inflammation and thymocyte depletion. While C57BL/6 mice showed a progressive and lethal disease, BALB/c mice partly recovered. To characterize these murine models more effectively, we studied the parasite burden, serum levels of major infection outcome-related cytokines, the in vitro features of T. cruzi infection in peritoneal macrophages and the immunophenotype of thymic cells. The greater disease severity of T. cruzi-infected C57BL/6 mice was not linked to an increased parasite load, as parasitaemia, myocardial parasite nests and amastigote counts in peritoneal macrophages were not different from those in BALB/c mice. Cortical thymocyte loss was accompanied by the presence of apoptotic bodies and fragmented nuclear DNA, whereas fluorocytometric analysis at 17 days postinfection (p.i.) revealed a more pronounced loss of CD4+ CD8+ cells in C57BL/6 mice. This group displayed higher levels of TNF-alpha on days 14 and 21 p.i., in the presence of lower IL-1beta and IL-10 concentrations by days 14 and 21, and days 7 and 14 p.i., respectively. Day-21 evaluation showed higher concentrations of nitrate and TNF-alpha soluble receptors in C57BL/6 mice with no differences in IFN-gamma levels, with respect to the BALB/c group. Increased morbidity of C57BL/6 T. cruzi-infected mice does not seem to result from an aggravated infection but from an unbalanced relationship between pro- and anti-inflammatory mediators.

Impairment of mammary lobular development induced by expression of TGFbeta1 under the control of WAP promoter does not suppress tumorigenesis in MMTV-infected transgenic mice.

It has previously been shown that transgenic female mice expressing TGFbeta1 under control of regulatory elements of the whey-acidic protein (WAP) gene were unable to lactate. This was due to the increased apoptosis of the cells committed to the lobular-lactogenic phenotype. Our goal was to determine whether the expression of WAP-TGFbeta1 transgene could inhibit MMTV (mouse mammary tumor virus) tumorigenic activity in the mammary gland. It is well known that the infection with this virus produces focal hyperplastic secretory nodules (HANs) and, some variants can also induce ductal pregnancy-dependent lesions (plaques). In either case, MMTV infection leads ultimately to the appearance of malignant mammary tumors. The results shown herein demonstrate that TGFbeta1 expression in the secretory mammary epithelium does not suppress mammary tumorigenesis in MMTV infected mice. Although MMTV infected WAP-TGFbeta1 transgenic females displayed a strong impairment of lobule-alveolar development, carcinogenesis induced by any of the four MMTV variants used herein proceeded unabated. WAP-TGFbeta1 tumors that showed a strong expression at the WAP promoter, appeared later and grew more slowly than their wild-type counterparts. Transgenic females also had a lower incidence of HANs and plaques. Our study suggests that the epithelial target cells for tumorigenic mutations are probably progenitor cells that are not susceptible to the apoptotic effect of TGFbeta1. Alternatively, their daughters cells that display the secretory phenotype and could be more involved in the formation of premalignant lesions continue to die due to the expression of the transgene.

Alterations during positive selection in the thymus of nackt CD4-deficient mice.

The T-cell repertoire is shaped by the positive and negative selection of immature CD4(+) CD8(+) double positive (DP) thymocytes. Positive selection of DP T cells to the CD4(+) CD8(-) and CD4(-) CD8(+) simple positive (SP) lineages is a multistep process which involves cellular interactions between thymocytes and stromal cells. Mutant nackt (nkt/nkt) mice have been shown to have a deficiency in the CD4(+) CD8(-) T-cell subset both in the thymus and in the periphery. The present report suggests that nkt/nkt mice present alterations in early steps of positive selection because they show decreases in the percentages of CD69(+) and CD5(+) cells within the DP subset. Experiments involving bone marrow transfer and thymic chimeras demonstrate that the thymic epithelium of nkt/nkt mice is involved in the alterations registered during positive selection and dictates the ultimate fate of CD4(+) SP cells.

Inhibition of metastases by a serum factor associated to concomitant resistance induced by unrelated murine tumors.

Murine lung metatases growing undisturbed by the primary tumor were significantly inhibited by the concomitant resistance induced by a secondary subcutaneous implant of two unrelated tumors. Such inhibition was T-independent since it was also observed in nude mice; its full expression was dependent on the presence of the secondary tumor implant and it was exerted on both macroscopic and microscopic established metastases and not on the process of tumor cell dissemination from the primary tumor. Direct and indirect mechanisms seemed to be involved, the former affecting the metastatic cells per se by causing a decrease in proliferation and an increase in apoptosis while the latter affected neo-vascularization. These antitumor and antiangiogenic effects could be attributed to a serum factor induced by the unrelated tumors generating concomitant resistance. This factor proved to be heat, acid and alkaline resistant and dialysable; it was recovered in an HPLC column with maximum absorption at 215 and 266 nm; it was anionic at neutral pH, exhibiting free carboxil groups and one or more molecules of tyrosine, with a molecular weight between 870 and 1300 Dalton. Intravenous administration of this factor significantly inhibited lung metastases, decreasing mitosis and increasing apoptosis similar to that observed in the presence of the unrelated tumors.

Characterization of two infectious mouse mammary tumour viruses: superantigenicity and tumorigenicity.

Mouse mammary tumour virus (MMTV) is a type B retrovirus that causes mammary tumours in susceptible mice. MMTV encodes a superantigen (SAg) that has the property of stimulating T-cell populations expressing a particular variable region of the T-cell receptor (TCR) beta chain (Vbeta) and needs to be presented in the context of major histocompatibility complex (MHC) class II molecules. Previously, we described two exogenous MMTV, MMTV BALB14, which encodes a superantigen that induces the deletion of Vbeta14+ Tcells, and MMTV BALB2, which encodes a SAg that induces the deletion of Vbeta2+ Tcells. We now describe their biological activity: the deletions involve both CD4+ and CD8+ populations, are progressive and can be detected in blood, lymph nodes and spleen. Such deletions reflect, at least in part, those occurring during intrathymic development. Both BALB2 and BALB14 viral variants are capable of inducing a strong increase of Vbeta-specific T cells in BALB/c mice (I-A+, I-E+). However, when injected into the footpad, their initial stimulatory capacity differs in that the presence of MHC I-E molecules is essential only for the stimulation of Vbeta2+ T cells. Both viral variants are able to induce deletion even in the absence of the I-E molecule in which case, however, deletion appears later and is less pronounced. Both exogenous MMTVs induce, at the end of a year, 30-35% of pregnancy-dependent mammary adenocarcinomas.

[Coevolutive mechanisms between retroviruses and their hosts. The murine mammary tumor model]. / Mecanismos coevolutivos entre los retrovirus y sus huéspedes. El modelo del tumor mamario murino.

Mouse mammary tumor virus (MMTV) is a type B retrovirus that is transmitted as an infectious milk-borne particle and that causes mammary carcinomas by insertional activation of cellular protooncogenes. Germ line infections result in endogenous Mtv proviruses integrated in the genome of most mouse strains. These endogenous proviruses have been integrated into the genomes of mice for only the past 3-5 million years. The open reading frame present in the 3' long terminal repeat (LTR) of the provirus encodes a superantigen (SAg) which is able to stimulate a large proportion of T cells sharing a common T-cell receptor beta chain variable domain (v beta). Expression of this SAg is critical to the MMTV life cycle. After expression of the SAg in B cells a significant number of T cells are recruited to respond to these MMTV infected cells. As a consequence both the T cells expressing the relevant TCR V beta domain and the infected B cells become activated and start dividing. This would facilitate integration of MMTV and amplify the number of virus infected lymphocytes. Most likely during lactation the mammary glands become receptive to viral infection. The presence of endogenous Mtvs induces an early clonal deletion of reactive T cells. For this reason it has been argued that the presence of these proviruses confers a selective advantage to the mouse population by protecting the host from infection with an exogenous MMTV coding for a cross-reactive SAg. However, recent results discussed herein suggest that Mtv proviruses may also be detrimental to the mouse population by participating in recombinations with exogenous MMTVs, giving rise to highly tumorigenic recombinant particles. These results are discussed in the light of recent reports suggesting the involvement of viral sequences with a high homology to MMTV in human mammary tumorigenesis.

[Superantigens and retroviral infections. Increase of mammary tumorigenicity due to recombination between exogenous and endogenous MMTV viruses]. / Superantígenos e infecciones retrovirales. Aumento de la tumorigenicidad mamaria por recombinación entre virus MMTV exógenos y endógenos.

A number of milk-borne exogenous mouse mammary tumor viruses (MMTV) infect mice shortly after birth and, when expressed, produce superantigens. Herein we describe the biological effects of new variants of exogenous MMTV: one of them (BALB14) present in BALB/c mice and showing a low ability to induce mammary tumors, and the other (MMTV-7) being the result of recombination between the BALB14 and the Mtv-7 endogenous provirus. The recombinant virus which has the SAg-specificity of Mtv-7 was amplified in BALB/c mice this fact correlating with a high incidence of mammary tumors. The role of strong SAgs in the mechanism by which the recombinant virus increases its title in a susceptible host is discussed. The results obtained suggest that the presence of non-productive endogenous proviruses--considered as conferring a selective advantage to the mouse population by protecting it from infection with exogenous MMTV--should also be advantageous to the pathogen by increasing its variability, thus broadening the host range and allowing the expansion of highly tumorigenic variants.

[Superantigens and murine mammary tumor retrovirus]. / Superantígenos y retrovirus del tumor mamario murino.

Hosts and their pathogens have co-evolved for millions of years, developing multiple and intimate interactions. Vertebrates have evolved a very complex immune system which pathogens have often been able to circumvent, in some cases even managing to appropriate some of its components for their own purpose. Among the pathogens which do use components of the immune system to survive and propagate, those coding for the expression of superantigens (SAgs) are now under intense scrutiny. Investigations concerning one of these pathogens, the mouse mammary tumor virus (MMTV), led to the understanding of how the expression of such components is a critical step in their life cycle. A number of milk-borne exogenous MMTV infect mice shortly after birth and, when expressed, produce superantigens. Herein, we describe the biological effects of new variants of MMTV. Two of these, BALB14 and BALB2 encoding SAgs with V beta 14+ and V beta 2+ specificities, respectively, were present in BALB/c mice of our colony (BALB/cT); a third variant, termed MMTV LA, originated in (BALB/cTxAKR)F1 mice from recombination between BALB 14 and Mtv-7 endogenous provirus. The recombinant LA virus induces the deletion of V beta 6+ and V beta 8.1+ T cells as a consequence of the acquisition of SAg hypervariable coding region of Mtv-7. The SAg encoded by MMTV LA strongly stimulates cognate T cells in vivo leading to a very effective amplification of lymphoid cells in BALB/c mice, correlating with a high incidence of mammary tumors. These results suggest that the presence of non-productive endogenous proviruses--generally considered to confer a selective advantage to the host by protecting it from infection with exogenous MMTVs encoding cross-reactive SAgs--could also be advantageous for the pathogen by increasing its variability, thus broadening the host range and allowing the expansion of highly tumorigenic variants.

Long-lasting functional unresponsiveness induced by a milk-transmitted Mls-1a-like superantigen.

We have recently shown (Piazzon et al. (1994) J. Immunol. 153, 1553) that foster-nursing of BALB/c mice on F1 Mls-1bxa mothers induce the progressive deletion of V beta 6+ and 8.1+ T cells in 50% of the mice. Preceding clonal deletion, a state of functional inactivation of CD4+ T cells to Mls-1a and anti-V beta 6 antibodies was detected in young mice. In the present paper we show that foster-nursing of BALB/c mice on (BALB/cxAKR)FI mothers is able to induce alterations in T cell reactivity in the non-deletor mice. Lymph node cells from foster-nursed mice show a decreased proliferative level against anti-V beta 6 antibodies and a diminished response in MLR and in CTL assays. The proliferative responses to either OVA or Con-A are also reduced. This state of functional inactivation is detected even in 6-month-old foster-nursed mice. Thus, the transmission through milk of the Mls-1a-like superantigen correlates in the non-deletor mice with a long-lasting state of functional inactivation and a decreased immune reactivity.

A maternally-inherited alteration in the T cell repertoire of BALB/c mice.

A number of milk-borne exogenous mammary tumor viruses (MMTV) infect mice shortly after birth and, when expressed, produce superantigens. The expression of these superantigens mediate the progressive deletion of T cells expressing specific V beta products. Here we describe a maternally-inherited alteration in the T cell repertoire in one colony of BALB/c mice which has not been reported up to now. This alteration involves the deletion of V beta 2+ and 14+ CD4+ T cells and correlates with a high incidence of mammary tumors, suggesting the involvement of a superantigen(s) probably transmitted through an exogenous MMTV in milk.

A maternally-inherited alteration in the T cell repertoire of BALB/c mice.

A number of milk-borne exogenous mammary tumor viruses (MMTV) infect mice shortly after birth and, when expressed, produce superantigens. The expression of these superantigens mediate the progressive deletion of T cells expressing specific V beta products. Here we describe a maternally-inherited alteration in the T cell repertoire in one colony of BALB/c mice which has not been reported up to now. This alteration involves the deletion of V beta 2+ and 14+ CD4+ T cells and correlates with a high incidence of mammary tumors, suggesting the involvement of a superantigen(s) probably transmitted through an exogenous MMTV in milk.

Transmission of an Mls-1a-like superantigen to BALB/c mice by foster-nursing on F1 Mls-1bxa mothers. Sex-influenced onset of clonal deletion.

Foster nursing of BALB/c (Mls-1b) mice on (BALB/cxAKR/J)F1 and (BALB/cxDBA/2)F1 (Mls-1bxa), but not on (BALB/cxC57Bl/6)F1 or (BALB/cxC3H/He)F1 (Mls-1bxb mothers, induced the progressive deletion of V beta 6+ and V beta 8.1+ T cells in 50% of the litter. The onset of this Mls-1a-like clonal deletion was markedly sex-influenced, being earlier in females (8-10 wk of age) than in males (32 wk). In both sexes, CD4+ V beta 6+ cells were more affected than CD8+ V beta 6+ cells. Decreases in the percentage of V beta 6+ cells were detected simultaneously in the thymus, lymph nodes, and peripheral blood. Preceding clonal deletion, functional unresponsiveness of CD4+ T cells to Mls-1 a Ags and to anti-V beta 6 Abs could be detected in most young male and female mice. The transmission of the Mls-1a-like superantigen through foster-nursing on (BALB/cxAKR/J)F1 mice correlated with the presence in milk of the mouse mammary tumor virus envelope protein gp52.

Regulation of parental alloreactivity by reciprocal F1 hybrids. The role of lactation.

Adult reciprocal F1 hybrids differ in their susceptibility to parental graft versus host (GvH) reactions. These reactions were lower when the donor strain was syngeneic with the maternal one. Splenocytes from the member of the reciprocal pair in which the GvH reactions were lower also induced a decreased response of parental cells in cytotoxicity assays and in mixed lymphocyte reactions (MLR). The treatment with anti-CD8 plus complement was able to abrogate the different stimulatory ability of the reciprocal F1 spleen populations. Foster-nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their splenocytes to induce both parental anti-F1 MLR and CTL. The stimulatory ability was indistinguishable from that observed in the reciprocal F1 combination nursed on its own mother. Moreover, lactation was able to alter the ability of CD8+ spleen cells to regulate CTL and parental anti-F1 MLR. The results reported herein show the existence of a maternal effect acting though milk capable of altering the regulation of parental alloreactive T reactions towards self histocompatibility antigens.

Neonatal thymic contrasuppressor activity on graft versus host reactions towards self histocompatibility antigens. Parental effects.

The ability of fetal and neonatal F1 thymocytes to regulate parental graft versus host (GvH) reactions against self histocompatibility antigens was investigated. The results obtained showed that: (1) fetal F1 thymocytes were able to suppress both maternal and paternal GvH reactivity; (2) at birth, thymocytes were still able to suppress maternal GvH reactivity while no suppression of paternal reactions was detected; the ability to suppress maternal GvH reactions could be detected until day 3; (3) the loss of suppressor activity correlated with the ability of thymocytes to contrasuppress parental GvH reactions. Thus, 24-h F1 thymocytes showed contrasuppressor activity on paternal GvH reactivity and 4-day thymocytes on maternal reactivity. Thymic cells with contrasuppressor activity were shown to be Lyt-1+, CD4+, CD8- and adherent to Vicia villosa. These results suggest the existence of parental effects influencing the duration of thymic suppression and the subsequent appearance of contrasuppressor activity on GvH reactions against self histocompatibility antigens, according to the maternal or paternal origin of self antigens towards which the reaction is directed.

Popliteal lymph node enlargement induced in syngeneic hosts by T cells from foster-nursed mice.

Splenocytes from adult F1 mice were assayed for their capacity to induce popliteal lymph node enlargement (PLNE) when inoculated in the footpad of identical or reciprocal F1 hosts. The results obtained showed that: (i) T Lyt 1+ splenocytes from adult F1 hybrids were able to induce a significant PLNE when inoculated in reciprocal but not in identical F1 hosts. (ii) Foster-nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their T splenocytes to induce PLNE: Lyt 1+ splenocytes were able to induce significant PLNE in identical but not in reciprocal F1 hosts. Thus, the ability of T splenocytes from foster-nursed F1 hybrids to induce PLNE resembled that observed in reciprocal F1 hybrids nursed by their own mothers. (iii) PLNE was accompanied by cell proliferation involving host B and T lymphocytes. (iv) This PLNE could be detected using F1 hybrids from parental strains differing or not at H-2 antigens but involving a parental strain expressing the stimulatory Mlsa allele and a parental strain bearing the nonstimulatory Mlsb allele while it was not observed in F1 hybrids from parental strains sharing Mlsa antigens.

[Ontogeny of T-cell recognition of self histocompatibility antigens: parenteral influences]. / Ontogenia del reconocimiento T de antígenos de histocompatibilidad propios: influencias parentales.

The existence of parental influences on the recognition of self histocompatibility was investigated. The results obtained showed that: 1) fetal liver and neonatal splenocytes and thymocytes from F1 mice differed in their capacity to regulate parental alloreactive T reactions against self histocompatibility antigens either of maternal or paternal origin. Fetal and neonatal F1 cells--until day 5--were able to suppress systemic and local GvH reactions induced in F1 hosts with maternal but not with paternal splenocytes; 2) this differential regulatory activity concerning parental GvH reactions against self histocompatibility antigens are correlated with the existence of a differential time lag in the appearance of thymic contrasuppressor activity on maternal anti-paternal and paternal anti-maternal GvH reactivity; 3) splenocytes from reciprocal F1 hybrids--from day 14 onwards--differed in their ability to stimulate F1 T cell proliferation in SMLC reactions; 4) foster nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their splenocytes to stimulate the proliferation of responder F1 T cells. The stimulatory ability of splenocytes from foster-nursed hybrids was indistinguishable from that observed in the reciprocal F1 combination nursed by their own mother, suggesting that lactation would be involved in the differences registered; 5) reciprocal F1 mice differed in their response to conventional antigens presented in the context of parental Ia antigens, lactation also being responsible for the induction of these differences. The different mechanisms involved in the alterations of the outcome of self recognition in the litter are discussed.

Ontogenia del reconocimiento T de antígenos de histocompatibilidad propios: influencias parentales. / [Ontogeny of T-cell recognition of self histocompatibility antigens: parenteral influences]

The existence of parental influences on the recognition of self histocompatibility was investigated. The results obtained showed that: 1) fetal liver and neonatal splenocytes and thymocytes from F1 mice differed in their capacity to regulate parental alloreactive T reactions against self histocompatibility antigens either of maternal or paternal origin. Fetal and neonatal F1 cells--until day 5--were able to suppress systemic and local GvH reactions induced in F1 hosts with maternal but not with paternal splenocytes; 2) this differential regulatory activity concerning parental GvH reactions against self histocompatibility antigens are correlated with the existence of a differential time lag in the appearance of thymic contrasuppressor activity on maternal anti-paternal and paternal anti-maternal GvH reactivity; 3) splenocytes from reciprocal F1 hybrids--from day 14 onwards--differed in their ability to stimulate F1 T cell proliferation in SMLC reactions; 4) foster nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their splenocytes to stimulate the proliferation of responder F1 T cells. The stimulatory ability of splenocytes from foster-nursed hybrids was indistinguishable from that observed in the reciprocal F1 combination nursed by their own mother, suggesting that lactation would be involved in the differences registered; 5) reciprocal F1 mice differed in their response to conventional antigens presented in the context of parental Ia antigens, lactation also being responsible for the induction of these differences. The different mechanisms involved in the alterations of the outcome of self recognition in the litter are discussed.