Inmunosenescencia prematura en ratones triple-transgénicos para la enfermedad del Alzheimer / Premature immunosenescence in triple-transgenic mice for Alzheimer's disease

Introducción. En la enfermedad del Alzheimer (EA) se ha comprobado que existe un deterioro en la comunicación neuroinmunoendocrina. Sin embargo, apenas hay estudios a un nivel periférico en esta enfermedad neurodegenerativa, en concreto en lo que respecta a la función inmunitaria. Dado que recientemente se ha establecido que ciertos parámetros de función inmunitaria son marcadores de la velocidad de envejecimiento y pueden predecir la longevidad, el propósito del presente trabajo fue valorar algunas de esas funciones en leucocitos esplénicos de ratones transgénicos para la EA de diversas edades. Material y métodos. Se emplearon ratones triple-transgénicos para la EA (3 xTgAD) hembras, así como sus controles no transgénicos (NTg) jóvenes (4 ± 1 meses), adultos (9 ± 1 meses) y maduros (12 ± 1 meses). Se valoraron la quimiotaxis, la actividad citotóxica de las «natural killer» (NK) y la respuesta linfoproliferativa en presencia de los mitógenos concanavalina A y lipopolisacárido en leucocitos esplénicos, funciones que disminuyen al envejecer. Además, se realizó una curva de supervivencia en otro grupo de animales 3 xTgAD y NTg. Resultados. En los 3 xTgAD, con respecto a los NTg, la quimiotaxis se encuentra disminuida en todas las edades, mientras que dicha disminución se observa a los 4 y 9 meses en la linfoproliferación y solo en los jóvenes en el caso de la actividad NK. Los 3 xTgAD mostraron una menor supervivencia que los NTg. Conclusiones. Los ratones 3 xTgAD presentan una inmunosenescencia prematura, lo que podría explicar su temprana mortalidad. La valoración a nivel periférico de las funciones inmunológicas estudiadas podría ser un indicador del desarrollo de la enfermedad de Alzheimer (AU)

Introduction. A deterioration of the neuroimmunoendocrine network has been observed in Alzheimer's disease (AD). However, the peripheral immune response has hardly been investigated in this pathology. Since some immune function parameters have been established as good markers of the rate of ageing, and can predict longevity, the aim of the present work was to study some of these functions in splenic leucocytes in transgenic mice for AD of different ages. Material and methods. Young female (4 ± 1 months), adult (9 ± 1 months), and mature (12 ± 1 months) triple-transgenic mice for AD (3 xTgAD) and non-transgenic (NTg) control mice of the same ages were used. The chemotaxis, the anti-tumour activity of «natural killer» (NK) cells and the lymphoproliferative response in the presence of the mitogens concanavalin A and lipopolysaccharide, functions that decrease with age, were determined in splenic leucocytes. In addition, the differences in lifespan between 3 xTgAD and NTg were studied in parallel using other animals, until their death through natural causes. Results. In 3 xTgAD, with respect to NTg, chemotaxis decreased at all ages studied, whereas in lymphoproliferative response this reduction was shown at 4 months and 9 months. NK activity was diminished only in young 3 xTgAD with respect to NTg. The 3 xTgAD showed a shorter lifespan than the NTg control group. Conclusions. The 3 xTgAD mice show a premature immunosenescence, which could explain their early mortality. The determination of these immune functions at peripheral level could serve as a marker of the progression of the Alzheimer's disease (AU)

Differential requirements of cellular and humoral immune responses for Fv2-associated resistance to erythroleukemia and for regulation of retrovirus-induced myeloid leukemia development.

To assess the possible contribution of host immune responses to the exertion of Fv2-associated resistance to Friend virus (FV)-induced disease development, we inoculated C57BL/6 (B6) mice that lacked various subsets of lymphocytes with FV containing no lactate dehydrogenase-elevating virus. Fv2(r) B6 mice lacking CD4(+) T cells developed early polycythemia and fatal erythroleukemia, while B6 mice lacking CD8(+) T cells remained resistant. Erythroid progenitor cells infected with spleen focus-forming virus (SFFV) were eliminated, and no polycythemia was observed in B cell-deficient B6 mice, but they later developed myeloid leukemia associated with oligoclonal integration of ecotropic Friend murine leukemia virus. Additional depletion of natural killer and/or CD8(+) T cells from B cell-deficient B6 mice resulted in the expansion of SFFV proviruses and the development of polycythemia, indicating that SFFV-infected erythroid cells are not only restricted in their growth but are actively eliminated in Fv2(r) mice through cellular immune responses.

Negative impact of IFN-γ on early host immune responses to retroviral infection.

The immune system is tasked with defending against a myriad of microbial infections, and its response to a given infectious microbe may be strongly influenced by coinfection with another microbe. It was shown that infection of mice with lactate dehydrogenase-elevating virus (LDV) impairs early adaptive immune responses to Friend virus (FV) coinfection. To investigate the mechanism of this impairment, we examined LDV-induced innate immune responses and found LDV-specific induction of IFN-α and IFN-γ. LDV-induced IFN-α had little effect on FV infection or immune responses, but unexpectedly, LDV-induced IFN-γ production dampened Th1 adaptive immune responses and enhanced FV infection. Two distinct effects were identified. First, LDV-induced IFN-γ signaling indirectly modulated FV-specific CD8+ T cell responses. Second, intrinsic IFN-γ signaling in B cells promoted polyclonal B cell activation and enhanced early FV infection, despite promotion of germinal center formation and neutralizing Ab production. Results from this model reveal that IFN-γ production can have detrimental effects on early adaptive immune responses and virus control.

The regulatory T-cell response during acute retroviral infection is locally defined and controls the magnitude and duration of the virus-specific cytotoxic T-cell response.

Cytotoxic CD8(+) T cells control acute viremia in many viral infections. However, most viruses that establish chronic infections evade destruction by CD8(+) T cells, and regulatory T cells (Treg) are thought to be involved in this immune evasion. We have infected transgenic mice, in which Treg can be selectively depleted, with Friend retrovirus (FV) to investigate the influence of Treg on pathogen-specific CD8(+) T-cell responses in vivo. We observed that Treg expansion during acute infection was locally defined to organs with high viral loads and massive activation of virus-specific effector CD8(+) T cells. Experimental ablation of Treg resulted in a significant increase of peak cytotoxic CD8(+) T-cell responses against FV. In addition, it prevented the development of functional exhaustion of CD8(+) T cells and significantly reduced FV loads in lymphatic organs. Surprisingly, despite the massive virus-specific CD8(+) T-cell response after temporary Treg depletion, no evidence of immunopathology was found. These results demonstrate the important role of Treg in controlling acute retrovirus-specific CD8(+) T-cell responses, and suggest that temporary manipulation of Treg might be a possible therapeutic approach in chronic infectious diseases.

Differential impact of the transcriptional repressor Gfi1 on mature CD4+ and CD8+ T lymphocyte function.

The transcriptional repressor Gfi1 is a nuclear zinc-finger protein that is expressed in T cell precursors in the thymus, but is down-regulated in mature, resting T cells. Gfi1 expression rises transiently to levels seen in thymocytes upon antigenic activation. We show here that lack of Gfi1 causes delayed cell cycle entry and apoptosis after antigenic stimulation in both mature CD4+ and CD8+ T cells ex vivo. DNA micro-array analysis demonstrated that this correlated with an up-regulation of the death receptor CD95, the proapoptotic factors Bad and Apaf1 and the cell cycle inhibitor p21, and a down-regulation of Bcl-2 expression in Gfi1-/- T cells. Surprisingly, while Gfi1-deficient CD4+ T cells showed the same defective behavior in vivo, Gfi1-deficient CD8+ T cells showed no aberration in vivo and were fully able to mount an anti-viral immune response. This indicates that Gfi1 exerts different functions in CD4+ and CD8+ T cells very likely by maintaining different genetic programs in both cell types, and appears to be essential for the CD4 helper T cell immune response but dispensable for the function of cytotoxic CD8+ T cells.

DNA vaccine against Friend erythroleukaemia virus.

Plasmids carrying DNA copies of the gag and env genes of FV, which causes erythroleukaemia in susceptible mouse strains, were prepared. Expression of the cloned genes was confirmed by indirect immunofluorescence in cells transfected in vitro. Immunization experiments were performed in DBA/2 mice. Animals were injected with three doses of plasmid either intramuscularly (100 microg DNA per dose) or intradermally (1 microg DNA per dose); in the latter case, a gene gun was used. The FV type A or P was used as a challenge. The immunization with gag- and env-derived vaccines resulted in protective immunity in a high proportion of mice.

Viral expressions in Reed-Sternberg cells.

In the murine system natural hybridoma formation was observed first in 1968-9. In the #620 to 818 system a mouse leukemia virus-(MLV-) producer diploid lymphoma cell fused with an immune plasma cell. The tetraploid fusion product cells grew in suspension cultures and as ascites tumors in mice and continued the production of MLV particles and MLV-neutralizing antibodies. Analogy between the #620 to 818 system and the origin of RS cells is proposed. Indirect evidence suggests retroviral infection of the mononuclear HD cell which presumably is an interdigitating reticulum (IR) cell. Reactive B and T cells interact in an abnormal manner and fuse with the retrovirally infected IR cell. The fusion product cells display hyperdiploidy and a disarray of markers as IR markers are lost due to dedifferentiation (and regained upon differentiation induction) and B and/or T cell markers are gained. Conventional theories for the origin of RS cells fail to explain the great heterogeneity of their markers. Derivation of RS cells from IR cells and B and/or T lymphocytes as natural hybridomas offers plausible explanation for all the features of RS cells.

Friend virus replication in normal and immunosuppressed C57BL/6 mice.

Young adult C57BL/6 mice are resistant to the replication of Friend virus. We show here that this resistance is not absolute. In 7-week old C57BL/6 mice injected with NB-tropic Friend virus iv, high titers of SFFV could be recovered from the spleen at 8 days after infection but by 21 days, no virus was detectable. A single dose of anti-Thy 1.2 monoclonal antibody iv before FV infection permitted continued replication of SFFV in these animals. This finding strongly supports the hypothesis that SFFV replication in C57BL/6 mice is restricted by a T cell-mediated immune response.