Identification of altered integrin alpha/beta chain expression on T cells from old mice infected with Mycobacterium tuberculosis

Extracellular Delivery of Functional Mitochondria Rescues the Dysfunction of CD4+ T Cells in Aging

Mitochondrial dysfunction alters cellular metabolism, increases tissue oxidative stress, and may be principal to the dysregulated signaling and function of CD4+ T lymphocytes in the elderly. In this proof of principle study, it is investigated whether the transfer of functional mitochondria into CD4+ T cells that are isolated from old mice (aged CD4+ T cells), can abrogate aging-associated mitochondrial dysfunction, and improve the aged CD4+ T cell functionality. The results show that the delivery of exogenous mitochondria to aged non-activated CD4+ T cells led to significant mitochondrial proteome alterations highlighted by improved aerobic metabolism and decreased cellular mitoROS. Additionally, mito-transferred aged CD4+ T cells showed improvements in activation-induced TCR-signaling kinetics displaying markers of activation (CD25), increased IL-2 production, enhanced proliferation ex vivo. Importantly, immune deficient mouse models (RAG-KO) showed that adoptive transfer of mito-transferred naive aged CD4+ T cells, protected recipient mice from influenza A and Mycobacterium tuberculosis infections. These findings support mitochondria as targets of therapeutic intervention in aging.

Modeling the Mycobacterium tuberculosis Granuloma - the Critical Battlefield in Host Immunity and Disease

Granulomas are the hallmark of Mycobacterium tuberculosis (M.tb) infection and thus sit at the center of tuberculosis (TB) immunopathogenesis. TB can result from either early progression of a primary granuloma during the infection process or reactivation of an established granuloma in a latently infected person. Granulomas are compact, organized aggregates of immune cells consisting of blood-derived infected and uninfected macrophages, foamy macrophages, epithelioid cells (uniquely differentiated macrophages), and multinucleated giant cells (Langerhans cells) surrounded by a ring of lymphocytes. The granuloma's main function is to localize and contain M.tb while concentrating the immune response to a limited area. However, complete eradication does not occur since M.tb has its own strategies to persist within the granuloma and to reactivate and escape under certain conditions. Thus M.tb-containing granulomas represent a unique battlefield for dictating both the host immune and bacterial response. The architecture, composition, function, and maintenance of granulomas are key aspects to study since they are expected to have a profound influence on M.tb physiology in this niche. Granulomas are not only present in mycobacterial infections; they can be found in many other infectious and non-infectious diseases and play a crucial role in immunity and disease. Here we review the models currently available to study the granulomatous response to M.tb.

Optimization of inhaled therapies for tuberculosis: the role of macrophages and dendritic cells

Inhaled therapies in the form of drugs or vaccines for tuberculosis treatment were reported about a decade ago. Experts around the world met to discuss the scientific progress in inhaled therapies at the international symposium "Optimization of inhaled Tuberculosis therapies and implications for host-pathogen interactions" held in New Delhi, India on November 3-5, 2009. The meeting was organized by the Central Drug Research Institute (CDRI) Lucknow, India. The lung is the main route for infection with Mycobacterium tuberculosis bacilli and the primary site of reactivation of latent disease. The only available vaccine BCG is relatively ineffective at preventing tuberculosis disease and current therapy requires prolonged treatment with drugs which results in low patient compliance. Consequently, there is a need to design new vaccines and therapies for this disease. Recently there has been increased interest in the development of inhaled formulations to deliver anti-mycobacterial drugs and vaccines directly to the lung and many of these therapies are designed to target lung macrophages and dendritic cells. However, the development of effective inhaled therapies requires an understanding of the unique function and immunosuppressive environment of the lung which is driven, in part, by alveolar macrophages and dendritic cells. In this review, we will discuss the role of alveolar macrophages and dendritic cells in the host immune response to M. tuberculosis infection and the ways in which inhaled therapies might enhance the anti-microbial response of phagocytes and boost pulmonary immunity.

Age-related differences in integrin expression in peripheral blood lymphocytes

Alpha integrins play an important role in cell to cell and cell to extra-cellular matrix interactions required for an effective T-lymphocyte-mediated immune response, however little is known about age related differences in expression of alpha integrins on T-cells in humans. We here measured alpha-4 (α4) integrin (CD49d) expression on T-lymphocytes via peripheral blood sampling, comparing parameters between cohorts of young and old adults. No age-related differences were found for the absolute numbers of T-cells, although the percentage of CD4+ T-cells in older adults was significantly greater and the percentage of CD8+ T-cells lower than in younger cohorts. Percentage and absolute numbers of CD3+ T-cells co-expressing CD49d were significantly lower in older adults compared to younger cohorts, and the percentage of gated CD4+ and CD8+ cells that co-labelled positively for CD49d was also reduced in this group. There were no age-related differences in circulating levels of cytokines (Type I interferons) that are known to regulate cell surface integrin expression. Reduced expression of alpha integrins on T-cells may be an early indicator of the loss of homeostatic control that occurs with ageing, contributing to diminished effector T-cell responses during senescence.

Interleukin-12 is sufficient to promote antigen-independent interferon-gamma production by CD8 T cells in old mice

Numerous functional defects have been identified in naive T cells from aged mice, including deficiencies in proliferation, cytokine production and signal transduction. It is well documented that the ratio of naïve to memory T cells significantly decreases with age resulting in the majority of T cells from aged hosts expressing activated/memory T-cell markers (CD44(hi)), yet it is unclear whether T cells with a CD44(hi) phenotype in aged hosts are functionally equivalent to T cells with a similar phenotype in young hosts. We have identified a population of CD44(hi) CD8 T cells in old mice that are capable of secreting interferon-gamma (IFN-gamma) in response to interleukin-12 (IL-12) stimulation. This occurred in the absence of T-cell receptor engagement, a function that was not observed in CD8 T cells from young mice. This phenotype was associated with increased IL-12 receptor beta2 gene expression and IL-12 induced signal transducer and activator of transcription 4 (STAT-4) activation, even when CD8 T-cell numbers from young and old mice were normalized for CD44(hi) expression. Furthermore, we demonstrate that IL-12-induced STAT-4 activation was required for T helper type 1 (Th1) cytokine-induced IFN-gamma production in CD8 T cells. These data illustrate that old mice possess a specialized subset of CD44(hi) CD8 T cells with an enhanced responsiveness to IL-12, enabling these cells to produce substantial amounts of IFN-gamma in response to Th1 cytokine stimulation. We have therefore identified a functional difference in the populations of CD44(hi) CD8 T cells from young and old mice, and believe that understanding age-associated immunological changes is essential for helping the elderly combat deadly diseases.

Factors influencing the protective efficacy of a BCG homologous prime-boost vaccination regime against tuberculosis

Tuberculosis due to Mycobacterium spp. continues to represent a major threat to human and animal health, prompting the search for effective vaccines. We have previously reported a sequential prime and boost homologous vaccination regime, using live avirulent M. bovis bacille Calmette-Guerin (BCG) strain 1173P2, that can provide significant protection to red deer (Cervus elaphus) against virulent M. bovis infection. Here, we have investigated the influence of varying the time-periods during and following the vaccination regime on the subsequent outcome of disease following post-vaccination pathogen challenge. Deer vaccinated using the standard regime of BCG-prime (week 0) and BCG-boost (week 8) followed by M. bovis challenge (week 14-16) were highly protected, showing significant reductions in the incidence of M. bovis infection and tuberculous lesions, as well as reduced pathogen burdens in sentinel lymphatic tissues. Decreasing the time-period between primary and secondary immunisations from 8 to 4 weeks had no significant impact on the protective efficacy afforded by BCG vaccination, while increasing this period to 43 weeks largely ablated protection. Increasing the time-period between secondary immunisation and M. bovis challenge from 6 to 26 or 52 weeks also had no significant impact on protection, suggesting that an appropriately timed BCG prime-boost vaccination regime can establish long-lasting protective immunological memory in deer. Finally, increasing the time-period between virulent M. bovis challenge and the subsequent post-mortem examination of disease outcome indicated that - once vaccinated by the standard prime-boost regime - deer remain refractory to disease if challenged and maintained for up to 52 weeks, suggesting that vaccinated animals harbouring low numbers of virulent M. bovis organisms do not succumb to disease activation over time. These findings are discussed in relation to concurrent measurements of in vivo and ex vivo immunological markers of disease and protection, as well as the wider implications of a standardised vaccine regimen for practical use in animal health.

The influence of age on immunity to infection with Mycobacterium tuberculosis

Changes within the immune system during aging lead to an elderly population that is both highly susceptible to infectious diseases and unresponsive to typical vaccine protocols. Using the murine model of tuberculosis, we have identified key differences in the generation of T-helper 1 cell immunity between old and young mice, and this information may be important for the design of new vaccines or post exposure therapies to protect the elderly against infectious diseases. In response to infection with Mycobacterium tuberculosis, it has been shown that the generation of antigen-specific CD4(+) T-cell immunity is impaired in old mice. In contrast, recent findings document that old mice display a transient enhanced resistance that occurs within the first 3 weeks of infection. Early resistance was associated with the presence of CD8(+) T cells and their ability to produce interferon-gamma (IFN-gamma) well before their young counterparts. Further investigation into the mechanism by which CD8(+) T cells are induced to secrete IFN-gammain vivo could provide an approach to enhance the effector function of these cells and subsequently protect elderly individuals from respiratory pathogens such as M. tuberculosis.