Bridget Carruthers

IL-10 Inhibits Mature Fibrotic Granuloma Formation during Mycobacterium tuberculosis Infection

Protective immunity and latent Mycobacterium tuberculosis infection in humans are associated with the formation of mature protective granulomas within the lung. Unfortunately, understanding the importance of such structures has been hindered by the lack of small-animal models that can develop mature granulomas. In this article, we describe for the first time, to our knowledge, the formation of mature, fibrotic M. tuberculosis–containing pulmonary granulomas in a mouse model of IL-10 deficiency (CBA/J IL-10−/−). Long-term control of M. tuberculosis infection in the absence of IL-10 was also associated with an early and enhanced capacity for Ag presentation and a significant increase in the generation of multifunctional T cells. Although IL-10 deficiency is known to enhance Th1 immune responses in general, we demonstrate in this study using transient anti–IL-10R treatment that it is the presence of IL-10 in vivo during the first month of M. tuberculosis infection that plays a definitive role in the inhibition of optimum protective immunity that can establish the environment for mature granuloma formation. Although the importance of IL-10 during M. tuberculosis infection has been debated, our data demonstrate that in CBA/J mice, IL-10 plays a significant early inhibitory role in preventing the development of protective immunity associated with containment of M. tuberculosis infection.

Characterization of lung inflammation and its impact on macrophage function in aging

Systemic inflammation that occurs with increasing age (inflammaging) is thought to contribute to the increased susceptibility of the elderly to several disease states. The elderly are at significant risk for developing pulmonary disorders and infectious diseases, but the contribution of inflammation in the pulmonary environment has received little attention. In this study, we demonstrate that the lungs of old mice have elevated levels of proinflammatory cytokines and a resident population of highly activated pulmonary macrophages that are refractory to further activation by IFN‐γ. The impact of this inflammatory state on macrophage function was determined in vitro in response to infection with M.tb. Macrophages from the lungs of old mice secreted more proinflammatory cytokines in response to M.tb infection than similar cells from young mice and also demonstrated enhanced M.tb uptake and P‐L fusion. Supplementation of mouse chow with the NSAID ibuprofen led to a reversal of lung and macrophage inflammatory signatures. These data indicate that the pulmonary environment becomes inflammatory with increasing age and that this inflammatory environment can be reversed with ibuprofen.

Clonal Expansions of CD8+ T Cells with IL-10 Secreting Capacity Occur during Chronic Mycobacterium tuberculosis Infection

The exact role of CD8+ T cells during Mycobacterium tuberculosis (Mtb) infection has been heavily debated, yet it is generally accepted that CD8+ T cells contribute to protection against Mtb. In this study, however, we show that the Mtb-susceptible CBA/J mouse strain accumulates large numbers of CD8+ T cells in the lung as infection progresses, and that these cells display a dysfunctional and immunosuppressive phenotype (PD-1+, Tim-3+, CD122+). CD8+ T cell expansions from the lungs of Mtb-infected CBA/J mice were also capable of secreting the immunosuppressive cytokine interleukin-10 (IL-10), although in vivo CD8+ T cell depletion did not significantly alter Mtb burden. Further analysis revealed that pulmonary CD8+ T cells from Mtb-infected CBA/J mice were clonally expanded, preferentially expressing T cell receptor (TcR) Vβ chain 8 (8.2, 8.3) or Vβ 14. Although Vβ8+ CD8+ T cells were responsible for the majority of IL-10 production, in vivo depletion of Vβ8+ did not significantly change the outcome of Mtb infection, which we hypothesize was a consequence of their dual IL-10/IFN-γ secreting profiles. Our data demonstrate that IL-10-secreting CD8+ T cells can arise during chronic Mtb infection, although the significance of this T cell population in tuberculosis pathogenesis remains unclear.

Killer Cell Lectin-Like Receptor G1 Deficiency Significantly Enhances Survival after Mycobacterium tuberculosis Infection

ABSTRACT The expression of T cell differentiation markers is known to increase during Mycobacterium tuberculosis infection, and yet the biological role of such markers remains unclear. We examined the requirement of the T cell differentiation marker killer cell lectin-like receptor G1 (KLRG1) during M. tuberculosis infection using mice deficient in KLRG1. KLRG1−/− mice had a significant survival extension after M. tuberculosis infection compared to wild-type controls, and maintained a significantly lower level of pulmonary M. tuberculosis throughout chronic infection. Improved control of M. tuberculosis infection was associated with an increased number of activated pulmonary CD4+ T cells capable of secreting gamma interferon (IFN-γ). Our report is the first to show an in vivo impact of KLRG1 on disease control.

H-2 alleles contribute to antigen 85-specific interferon-gamma responses during Mycobacterium tuberculosis infection.

The in vitro immune responses to mycobacterial antigens have been linked to the H-2 loci in mice. We evaluated in vitro and in vivo immune responses during early Mycobacterium tuberculosis (M.tb) pulmonary infection of C57BL/6 (H-2(b)), C57BL/6 (H-2(k)), CBA/J (H-2(k)), and C3H/HeJ (H-2(k)) mice to determine H-2(k)-dependent and -independent effects. H-2(k)-dependent effects included delayed and diminished Ag85-specific Th1 cell priming, a reduced frequency of Ag85-specific IFN-γ producing cells, reduced IFN-γ protein in vivo, and increased M.tb lung burden as demonstrated by C57BL/6 H-2(k) mice vs. C57BL/6 mice. H-2(k)-independent factors controlled the amount of Ag85-specific IFN-γ produced by each cell, T cell numbers, granuloma size, and lymphocytic infiltrates in the lungs. Overall, these results suggest that an H-2(k)-dependent suboptimal generation of Ag85-specific cells impairs control of early M.tb growth in the lungs. H-2(k)-independent factors influence the potency of IFN-γ producing cells and immune cell trafficking during pulmonary M.tb infection.

Validation of Increased Blood Storage Times with the T-SPOT.TB Assay with T-Cell Xtend Reagent in Individuals with Different Tuberculosis Risk Factors

ABSTRACT We compared the performance of the T-SPOT.TB assay with blood used within 0 to 3.5 h after collection (control) to its performance with blood stored for 0 to 3.5, 5 to 8, 18 to 21, or 31 to 33 h with the addition of T-Cell Xtend (experimental), using samples from 154 participants. The 95.4% concordance between paired specimens indicated that blood can be stored for up to 33 h prior to T-SPOT.TB testing.

CBA/J mice generate protective immunity to soluble Ag85 but fail to respond efficiently to Ag85 during natural Mycobacterium tuberculosis infection.

In CBA/J mice, susceptibility to Mycobacterium tuberculosis (M.tb) is associated with low interferon‐gamma (IFN‐γ) responses to antigens (Antigen 85 (Ag85) and early secreted antigenic target‐6 (ESAT‐6)) that have been defined as immunodominant. Here, we asked whether the failure of CBA/J mice to recognize Ag85 is a consequence of M.tb infection or whether CBA/J mice have a general defect in generating specific T‐cell responses to this protein antigen. We compared CBA/J mice during primary M.tb infection, Ag85 vaccination followed by M.tb challenge, or M.tb memory immune mice for their capacity to generate Ag85‐specific IFN‐γ responses and to control M.tb infection. CBA/J mice did not respond efficiently to Ag85 in the context of natural infection or re‐infection. In contrast, CBA/J mice could generate Ag85‐specific IFN‐γ responses and protective immunity when this antigen was delivered as a soluble protein. Our data indicate that although M.tb infection of CBA/J mice does not drive an Ag85 response, these mice can fully and protectively respond to Ag85 if it is delivered as a vaccine. The data from this experimental model suggest that the Ag85‐containing vaccines in clinical trials should protect M.tb susceptible humans.

The Influence of Increasing Age on Susceptibility of the Elderly to Tuberculosis

The elderly are susceptible to infection with the bacterial pathogen Mycobacterium tuberculosis, and to the de- velopment of active TB disease. In this review we utilize experimental data from animal models to discuss the concept that age-associated changes in immune function are a critical parameter that contributes to the increased susceptibility of the elderly to M. tuberculosis infection.

Mycobacterium tuberculosis infected CBA/J mice can generate robust and protective responses to antigen Ag85 when delivered as a soluble protein, but fail to respond efficiently in the context of natural infection

In CBA/J mice, susceptibility to Mycobacterium tuberculosis (M.tb) is associated with low interferon‐gamma (IFN‐γ) responses to antigens (Antigen 85 (Ag85) and early secreted antigenic target‐6 (ESAT‐6)) that have been defined as immunodominant. Here, we asked whether the failure of CBA/J mice to recognize Ag85 is a consequence of M.tb infection or whether CBA/J mice have a general defect in generating specific T‐cell responses to this protein antigen. We compared CBA/J mice during primary M.tb infection, Ag85 vaccination followed by M.tb challenge, or M.tb memory immune mice for their capacity to generate Ag85‐specific IFN‐γ responses and to control M.tb infection. CBA/J mice did not respond efficiently to Ag85 in the context of natural infection or re‐infection. In contrast, CBA/J mice could generate Ag85‐specific IFN‐γ responses and protective immunity when this antigen was delivered as a soluble protein. Our data indicate that although M.tb infection of CBA/J mice does not drive an Ag85 response, these mice can fully and protectively respond to Ag85 if it is delivered as a vaccine. The data from this experimental model suggest that the Ag85‐containing vaccines in clinical trials should protect M.tb susceptible humans.

CBA/J mice generate protective immunity to soluble Ag85 but fail to respond efficiently to Ag85 during natural Mycobacterium tuberculosis infection: Immunity to Infection

In CBA/J mice, susceptibility to Mycobacterium tuberculosis (M.tb) is associated with low interferon‐gamma (IFN‐γ) responses to antigens (Antigen 85 (Ag85) and early secreted antigenic target‐6 (ESAT‐6)) that have been defined as immunodominant. Here, we asked whether the failure of CBA/J mice to recognize Ag85 is a consequence of M.tb infection or whether CBA/J mice have a general defect in generating specific T‐cell responses to this protein antigen. We compared CBA/J mice during primary M.tb infection, Ag85 vaccination followed by M.tb challenge, or M.tb memory immune mice for their capacity to generate Ag85‐specific IFN‐γ responses and to control M.tb infection. CBA/J mice did not respond efficiently to Ag85 in the context of natural infection or re‐infection. In contrast, CBA/J mice could generate Ag85‐specific IFN‐γ responses and protective immunity when this antigen was delivered as a soluble protein. Our data indicate that although M.tb infection of CBA/J mice does not drive an Ag85 response, these mice can fully and protectively respond to Ag85 if it is delivered as a vaccine. The data from this experimental model suggest that the Ag85‐containing vaccines in clinical trials should protect M.tb susceptible humans.