Kiki Tesselaar

CD27 is required for generation and long-term maintenance of T cell immunity

The Traf-linked tumor necrosis factor receptor family member CD27 is known as a T cell costimulatory molecule. We generated CD27−/− mice and found that CD27 makes essential contributions to mature CD4+ and CD8+ T cell function: CD27 supported antigen-specific expansion (but not effector cell maturation) of naïve T cells, independent of the cell cycle–promoting activities of CD28 and interleukin 2. Primary CD4+ and CD8+ T cell responses to influenza virus were impaired in CD27−/− mice. Effects of deleting the gene encoding CD27 were most profound on T cell memory, reflected by delayed response kinetics and reduction of CD8+ virus-specific T cell numbers to the level seen in the primary response. This demonstrates the requirement for a costimulatory receptor in the generation of T cell memory.

In vivo labeling with 2H2O reveals a human neutrophil lifespan of 5.4 days

Neutrophils are essential effector cells of the innate immune response and are indispensable for host defense. Apart from their antimicrobial functions, neutrophils inform and shape subsequent immunity. This immune modulatory functionality might however be considered limited because of their generally accepted short lifespan (< 1 day). In contrast to the previously reported short lifespans acquired by ex vivo labeling or manipulation, we show that in vivo labeling in humans with the use of (2)H(2)O under homeostatic conditions showed an average circulatory neutrophil lifespan of 5.4 days. This lifespan is at least 10 times longer than previously reported and might lead to reappraisal of novel neutrophil functions in health and disease.

Maintenance of Peripheral Naive T Cells Is Sustained by Thymus Output in Mice but Not Humans

Parallels between T cell kinetics in mice and men have fueled the idea that a young mouse is a good model system for a young human, and an old mouse, for an elderly human. By combining in vivo kinetic labeling using deuterated water, thymectomy experiments, analysis of T cell receptor excision circles and CD31 expression, and mathematical modeling, we have quantified the contribution of thymus output and peripheral naive T cell division to the maintenance of T cells in mice and men. Aging affected naive T cell maintenance fundamentally differently in mice and men. Whereas the naive T cell pool in mice was almost exclusively sustained by thymus output throughout their lifetime, the maintenance of the adult human naive T cell pool occurred almost exclusively through peripheral T cell division. These findings put constraints on the extrapolation of insights into T cell dynamics from mouse to man and vice versa.

Constitutive CD27/CD70 Interaction Induces Expansion of Effector-Type T Cells and Results in IFNγ-Mediated B Cell Depletion

The interaction between the TNF receptor family member CD27 and its ligand CD70 provides a costimulatory signal for T cell expansion. Normally, tightly regulated expression of CD70 ensures the transient availability of this costimulatory signal. Mice expressing constitutive CD70 on B cells had higher peripheral T cell numbers that showed increased differentiation toward effector-type T cells. B cell numbers in CD70 transgenic (TG) mice progressively decreased in primary and secondary lymphoid organs. This B cell depletion was caused by CD27-induced production of IFNgamma in T cells. We conclude that apart from its role in controlling the size of the activated T cell pool, CD27 ligation contributes to immunity by facilitating effector T cell differentiation.

Expression of the murine CD27 ligand CD70 in vitro and in vivo

The interaction between TNFR family member CD27 and its ligand CD70 promotes lymphocyte expansion and effector cell formation. In humans, control of CD27 function is partly regulated by the restricted expression of CD70. We used newly developed mAbs to characterize murine (m) CD70 expression in vitro and in vivo. On resting lymphocytes and immature dendritic cells (DC), mCD70 is absent. In vitro, Ag receptor triggering induced mCD70 mRNA in T cells, but cell surface protein expression was very low. Activated B cells synthesized much higher levels of mCD70 mRNA than activated T cells and clearly expressed mCD70 at the cell surface. mCD70 cell surface expression could also be induced on the DC line D1 and on in vitro-generated murine DC upon maturation. In lymphoid organs of naive mice, virtually no mCD70-expressing cells were found, with exception of cells in the thymic medulla, which may be epithelial in origin. However, after intranasal infection with influenza virus, lung-infiltrating T cells and T and B cells in draining lymph nodes expressed mCD70 according to immunohistology. In such activated lymphocytes, mCD70 protein is largely retained intracellularly. Plasma membrane expression of mCD70 was only detectable by flow cytometry on a small proportion of lung-infiltrating T cells and peaked at the height of the primary response. Thus, expression of CD70 in the mouse is highly regulated at the transcriptional and posttranslational level. This most likely serves to limit excessive effector cell formation after antigenic stimulation.

CD27 deficiency is associated with combined immunodeficiency and persistent symptomatic EBV viremia

BACKGROUND CD27 is a lymphocyte costimulatory molecule that regulates T-cell, natural killer (NK) cell, B-cell, and plasma cell function, survival, and differentiation. On the basis of its function and expression pattern, we considered CD27 a candidate gene in patients with hypogammaglobulinemia. OBJECTIVE We sought to describe the clinical and immunologic phenotypes of patients with genetic CD27 deficiency. METHODS A molecular and extended immunologic analysis was performed on 2 patients lacking CD27 expression. RESULTS We identified 2 brothers with a homozygous mutation in CD27 leading to absence of CD27 expression. Both patients had persistent symptomatic EBV viremia. The index patient was hypogammaglobulinemic, and immunoglobulin replacement therapy was initiated. His brother had aplastic anemia in the course of his EBV infection and died from fulminant gram-positive bacterial sepsis. Immunologically, lack of CD27 expression was associated with impaired T cell-dependent B-cell responses and T-cell dysfunction. CONCLUSION Our findings identify a role for CD27 in human subjects and suggest that this deficiency can explain particular cases of persistent symptomatic EBV viremia with hypogammaglobulinemia and impaired T cell-dependent antibody generation.

Sparse production but preferential incorporation of recently produced naïve T cells in the human peripheral pool

In mice, recent thymic emigrants (RTEs) make up a large part of the naïve T cell pool and have been suggested to be a distinct short-lived pool. In humans, however, the life span and number of RTEs are unknown. Although 2H2O labeling in young mice showed high thymic-dependent daily naïve T cell production, long term up- and down-labeling with 2H2O in human adults revealed a low daily production of naïve T cells. Using mathematical modeling, we estimated human naïve CD4 and CD8 T cell half-lives of 4.2 and 6.5 years, respectively, whereas memory CD4 and CD8 T cells had half-lives of 0.4 and 0.7 year. The estimated half-life of recently produced naïve T cells was much longer than these average half-lives. Thus, our data are incompatible with a substantial short-lived RTE population in human adults and suggest that the few naïve T cells that are newly produced are preferentially incorporated in the peripheral pool.

What's your age again? Determination of human neutrophil half-lives revisited

Neutrophils are the most abundant white blood cells and are indispensable for host defense. Recently, they have also been implicated in immune regulation and suppression. The latter functions seem hard to reconcile with the widely held view that neutrophils are very short‐lived, with a circulatory half‐life of <7 h. To reopen the discussion on the average neutrophil half‐life, we review and discuss experiments performed in the 1950s, 1960s, and 1970s, as well as recent in vivo labeling experiments. We reappraise the current knowledge on neutrophil half‐lives, including their production in the bone marrow, their residency in the circulation and marginated pool, and their exit from the circulation.

Signaling through CD70 Regulates B Cell Activation and IgG Production

CD70, the cellular ligand of the TNF receptor family member CD27, is expressed transiently on activated T and B cells and constitutively on a subset of B cell chronic lymphocytic leukemia and large B cell lymphomas. In the present study, we used B cells constitutively expressing CD70 to study the functional consequences of signaling through CD70. In vitro, CD70 ligation with anti-CD70 mAbs strongly supported proliferation and cell cycle entry of B cells submitogenically stimulated with either anti-CD40 mAb, LPS, or IL-4. In this process, the cell surface receptors CD25, CD44, CD69, CD95, and GL7 were up-regulated, whereas the expression of CD21, CD62L, surface IgM (sIgM), and sIgD was decreased. Addition of CD70 mAb to low dose LPS-stimulated CD70-positive B cells strongly diminished IgG secretion and enhanced production of IgM. Signaling through CD70 on B cells was dependent on the initiation of both PI3K and MEK pathways. In vivo exposure to either CD70 mAb or the CD70 counterreceptor CD27 down-regulated CD62L and sIgM on CD70-positive B cells. CD70 signaling during T cell-dependent immune responses also decreased IgG-specific Ab titers. Together, the in vitro and in vivo data demonstrate that CD70 has potent reverse signaling properties in B cells, initiating a signaling cascade that regulates expansion and differentiation.

Properties of murine CD8+CD27– T cells

In humans, loss of CD27 expression is associated with the stable acquisition of effector functions by CD8+ T cells. We found that murine CD8+CD27– T cells were confined to the primed CD62Ldull/–CD44brightCCR7– T cell population. CD8+CD27– T cells were absent from lymph nodes but could be found in blood, spleen and in non‐lymphoid organs such as lung and liver. Late after primary influenza virus infection, low percentages of antigen‐specific CD27– cells emerged in the lung and spleen. After recovery from secondary influenza virus infection, high percentages of influenza‐specific CD27– T cells were found in the lung and the loss of CD27 on lung CD8+ T cells coincided with high granzyme B expression. After murine cytomegalovirus infection, loss of CD27 expression on virus‐specific CD8+ T cell populations was sustained and especially marked in liver and lung. We suggest that in mice, CD27 is lost from CD8+ T cells only after repetitive antigenic stimulation. Moreover, the high expression of both granzyme B and perforin in the CD27– T cells suggests that the lack of CD27 on murine CD8+ T cells can be used to identify memory T cells with expression of cytotoxic effector molecules.