Scrub typhus is caused by the obligate intracellular rickettsiaOrientia tsutsugamushi (previously called Rickettsia tsutsugamushi). The bacterium is maternally inherited in trombicuid mites and transmitted to humans by feeding larvae. We report here the 2,127,051-bp genome of the Boryong strain, which represents the most highly repeated bacterial genome sequenced to date. The repeat density of the scrub typhus pathogen is 200-fold higher than that of its close relative Rickettsia prowazekii, the agent of epidemic typhus. A total of 359 tra genes for components of conjugative type IV secretion systems were identified at 79 sites in the genome. Associated with these are >200 genes for signaling and host-cell interaction proteins, such as histidine kinases, ankyrin-repeat proteins, and tetratrico peptide-repeat proteins. Additionally, the O. tsutsugamushi genome contains >400 transposases, 60 phage integrases, and 70 reverse transcriptases. Deletions and rearrangements have yielded unique gene combinations as well as frequent pseudogenization in the tra clusters. A comparative analysis of the tra clusters within the genome and across strains indicates sequence homogenization by gene conversion, whereas complexity, diversity, and pseudogenization are acquired by duplications, deletions, and transposon integrations into the amplified segments. The results suggest intragenomic duplications or multiple integrations of a massively proliferating conjugative transfer system. Diversifying selection on host-cell interaction genes along with repeated population bottlenecks may drive rare genome variants to fixation, thereby short-circuiting selection for low complexity in bacterial genomes.bacterial genome ͉ duplication ͉ repeats

We investigated the effects of aging on the IL-7-mediated CD8 ؉ T-cell survival pathway and of IL-7 therapy on T-cell immunity. Cells expressing IL-7 receptor (IL-7R) ␣ high and ␣ low were identified in a CD45RA ؉ effector memory (EM CD45RA؉ , CD45RA ؉ CCR7 ؊ ) CD8 ؉ T-cell subset. Elderly subjects (65 years and older) had an increased frequency of EM CD45RA؉ IL-7R␣ low CD8 ؉ T cells, leading to decreased STAT5 phosphorylation and survival responses to IL-7 compared with young subjects (40 years and younger). These EM CD45RA؉ IL-7R␣ low cells were largely antigen experienced (CD27 ؊ CD28 ؊ ), replicatively senescent (CD57 ؉ ), and perforin high CD8 ؉ T cells that had decreased IL-7R␣ mRNA, independent of guanine and adenine binding protein ␣ (GABP␣) and growth factor independence-1 (GFI1) expression. In measuring T-cell receptor (TCR) repertoires of EM CD45RA؉ CD8 ؉ T cells, the elderly had a limited repertoire in IL-7R␣ high and IL-7R␣ low cells, whereas the young had a diverse repertoire in IL-7R␣ high but not in IL-7R␣ low cells. These findings suggest that aging affects IL-7R␣ expression by EM CD45RA؉ CD8 ؉ T cells, leading to impaired signaling and survival responses to IL-7, and that IL-7 therapy may improve the survival of EM CD45RA؉ CD8 ؉ T cells with a diverse TCR repertoire in the young but not in the elderly. IntroductionThe proper development and maintenance of naive and memory CD8 ϩ T cells are essential for host defense. 1,2 IL-7, a member of the common cytokine-receptor ␥-chain (␥c) family, is critically implicated in the generation and maintenance of naive and memory CD8 ϩ and CD4 ϩ T cells. 3-8 IL-7 is produced by multiple stromal tissues, including epithelial cells in the thymus and bone marrow. 7 The IL-7R complex consists of 2 chains, the high-affinity IL-7R␣ chain and ␥c. 9 IL-7 binding to the receptor induces sequential phosphorylation of Jak1, Jak3, and STAT5, leading to the upregulation of Bcl-2, which promotes cell survival. 10,11 IL-7 regulates peripheral homeostasis of CD4 ϩ and CD8 ϩ T cells by promoting cell survival. When CD8 ϩ T cells from IL-7R intact and knockout (KO) mice were adoptively transferred to wild-type mice, cells from IL-7R KO mice had decreased survival compared with those from IL-7R intact mice. 3 Furthermore, in mice infected with lymphocyte choriomeningitis virus, IL-7R␣ high CD8 ϩ T cells had better survival and differentiation into memory cells than IL-7R␣ low CD8 ϩ T cells. 5 Alterations in T-cell immunity occur with aging. These alterations include thymic atrophy and changes in T-cell subsets and function, which likely contribute to increased risk for infection in the elderly. 12,13 For example, in 1998, 82 989 deaths in persons 65 and older in the United States were attributed to influenza and pneumonia, compared with 5969 deaths in persons aged 15 to 64. 14 In addition, CD4 ϩ and CD8 ϩ T-cell responses to the influenza vaccine were decreased in elderly subjects compared with young subjects. 15,16 Although the underlying mechanism for altered T-cell immune r...

α-Enolase (ENO1) is a multifunctional glycolytic enzyme expressed abundantly in the cytosol. It has been implicated in autoimmune and inflammatory diseases. Serum Abs against ENO1 were reported in rheumatoid arthritis (RA). Cell-surface expression of ENO1 has been found to be increased rapidly in response to inflammatory stimuli, but its expression and function has not been reported in RA. In this study, we show that cell-surface expression of ENO1 is increased on monocytes and macrophages isolated from RA patients but not on those from osteoarthritis patients, and Ab against ENO1 can stimulate these cells to produce higher amounts of proinflammatory mediators, such as TNF-α, IL-1 α/β, IFN-γ, and PGE2 via p38 MAPK and NF-κB pathway. The frequency of ENO1-positive cells in synovial fluid mononuclear cells was higher than PBMCs. ENO1-positive cells were also found in the inflamed synovium from RA patients and arthritic ankle tissues of mice with collagen-induced arthritis. Taken together, these findings suggest that Abs against ENO1 present in RA sera may stimulate monocytes and macrophages expressing cell-surface ENO1 and contribute to production of proinflammatory mediators during the effector phase of synovial inflammation.

Alterations in immunity that occur with aging likely contribute to the development of infection, malignancy and inflammatory diseases. Naturally occurring CD4 + regulatory T cells (Treg) expressing high levels of CD25 and forkhead box P3 (FOXP3) are essential for regulating immune responses. Here we investigated the effect of aging on the number, phenotypes and function of CD4 + Treg in humans. The frequency and phenotypic characteristics of CD4 + ,FOXP3 + T cells as well as their capacity to suppress inflammatory cytokine production and proliferation of CD4 + ,CD25 − T cells (target cells) were comparable in young (age ≤ 40) and elderly (age ≥ 65) individuals. However, when CD4 + ,FOXP3 + Treg and CD4 + ,CD25 − T cells were co-cultured at a ratio of 1:1, the production of anti-inflammatory cytokine IL-10 from CD4 + ,CD25 − T cells was more potently suppressed in the elderly than in the young. This finding was not due to changes in CTLA-4 expression or apoptosis of CD4 + ,FOXP3 + Treg and CD4 + ,CD25 − T cells. Taken together, our observations suggest that aging may affect the capacity of CD4 + ,FOXP3 + T cells in regulating IL-10 production from target CD4 + T cells in humans although their other cellular characteristics remain unchanged.

We hypothesized that immune response may contribute to progression of coronavirus disease-19 at the second week of illness. Therefore, we compared cell-mediated immune (CMI) responses between severe and mild COVID-19 cases. Methods: We examined peripheral blood mononuclear cells of laboratory-confirmed COVID-19 patients from their first and third weeks of illness. Severe pneumonia was defined as an oxygen saturation 93% at room air. Expressions of molecules related to T-cell activation and functions were analyzed by flow cytometry.Results: The population dynamics of T cells at the first week were not different between the two groups. However, total numbers of CD4 + and CD8 + T cells tended to be lower in the severe group at the third week of illness. Expressions of Ki-67, PD-1, perforin, and granzyme B in CD4 + or CD8 + T cells were significantly higher in the severe group than in the mild group at the third week. In contrast to the mild group, the levels of their expression did not decrease in the severe group. Conclusions: Severe COVID-19 had a higher degree of proliferation, activation, and cytotoxicity of T-cells at the late phase of illness without cytotoxic T-cell contraction, which might contribute to the development of severe COVID-19.

Mesenchymal stem cells (MSCs) are of therapeutic importance in the fields of regenerative medicine and immunological diseases. Accordingly, studies evaluating MSCs for clinical applications are increasing. In this study, we characterized MSCs from the periodontal ligament, umbilical cord (UC-MSCs), and adipose tissue, which were relatively easy to obtain with limited ethical concerns regarding their acquisition, and compared their immunological characteristics. Among MSCs isolated from the three different tissues, UC-MSCs grew the fastest in vitro. The three types of MSCs were shown to inhibit proliferation of activated peripheral blood mononuclear cells (PBMCs) to a similar degree, via the indoleamine 2,3-dioxygenase and cyclooxygenase-2 pathways. They were also shown to inhibit the proliferation of PBMCs using HLA-G, which was most prominent in UC-MSCs. Unlike the other two types of MSCs, UC-MSCs showed minimal expression of HLA-DR after activation, suggesting that they pose minimal risk of initiating an allogeneic immune response when administered in vivo. These characteristics, the ease of collection, and the minimal ethical concerns regarding their use suggest UC-MSCs to be suitable MSC therapeutic candidates.

Cytokines IL-7 and IL-15 are essentially involved in T-cell homeostasis. IL-7 is required for developing mature T cells in the thymus, whereas in the periphery, it promotes the survival of naïve and memory T cells by upregulating the antiapoptotic molecule Bcl-2. IL-15 potently induces the proliferation of memory CD8+ T cells independently of antigen and augments their effector function. Although IL-7 and IL-15 may help to defend the host against microorganisms and tumors by promoting T-cell immunity, dysregulated production of IL-7 and IL-15 can be harmful. In fact, increased levels of IL-15 in the circulation and inflamed tissues have been reported in various autoimmune diseases, including rheumatoid arthritis (RA), possibly contributing to the pathogenesis. In addition, IL-7, which may induce the production of inflammatory cytokines from T cells and monocytes, are found to be elevated in the joints of patients with RA. Here, we review what is currently known about the roles of these cytokines in T-cell immunity, in general, as well as in RA, in particular, focusing on recent discoveries.

Little is known about the cellular characteristics of CD8(+) T cells in rheumatoid arthritis (RA). We addressed this by investigating whether the frequency of the CD8(+) T cell subsets and their phenotypic characteristics are altered in the peripheral blood and synovial fluid (SF) from patients with RA. In this study, CD8(+) T cells, mainly CD45RA(-) effector memory (EM) CD8(+) T cells, were increased significantly in the SF, but not in the peripheral blood from RA patients, compared with healthy controls. The synovial EM CD8(+) T cells were activated phenotypes with high levels of CD80, CD86, and PD-1, and had a proliferating signature in vivo upon Ki-67 staining, whereas the Fas-positive cells were prone to apoptosis. In addition, EM CD8(+) T cells in the SF were less cytotoxic, as they expressed less perforin and granzyme B. In particular, the proportions of synovial fluid mononuclear cells that were CCR4(+)CD8(+) T cells and IL-4-producing CD8(+) T cells (i.e., Tc2 cells) were significantly higher than those in peripheral blood mononuclear cells of patients with RA and healthy controls. In addition, the number of IL-10-producing CD8(+) suppressor T (Ts) cells increased significantly in the SF of RA patients. Especially, CD8(+) T cells were inversely correlated with disease activity. These findings strongly suggest that EM CD8(+) T cells in the SF are increased, likely because of inflammation, and they may be involved in modulating inflammation, thereby affecting the development and progression of RA.