A subset of NK cells bears incomplete V(D)J rearrangements, but neither the consequence to cell activities nor the precise developmental stages in which recombination occurs is known. These are ...important issues, as recombination errors cause cancers of the B and T lineages. Using transgenic recombination reporter mice to examine NK cell dynamics in vivo, we show that recombination(+) NK cells have distinct developmental patterns in the BM, including reduced homeostatic proliferation and diminished Stat5 phosphorylation. In the periphery, both recombination(+) and recombination(-) NK cells mediate robust functional responses including IFN-gamma production, cytolysis, and tumor homing, suggesting that NK cells with distinct developmental histories can be found together in the periphery. We also show that V(D)J rearrangement marks both human cytolytic (CD56(dim)) and immunoregulatory (CD56(bright)) populations, demonstrating the distribution of permanent DNA rearrangements across major NK cell subsets in man. Finally, direct quantification of rag transcripts throughout NK cell differentiation in both mouse and man establishes the specific developmental stages that are susceptible to V(D)J rearrangement. Together, these data demonstrate that multipotent progenitors rather than lineage-specified NK progenitors are targets of V(D)J recombination and that NK cells bearing the relics of earlier V(D)J rearrangements have different developmental dynamics but robust biological capabilities in vivo.
Chronic lymphocytic leukemia (CLL) is a common malignancy characterized by the accumulation of B lymphocytes with an antigen-experienced activated CD19(+)CD5(+) clonal phenotype. Clinically, ∼50% of ...cases will behave more aggressively. Here, we investigate the role of the major B-cell transcription factor E2A, a known regulator of B-cell survival and proliferation, to CLL persistence. We show that E2A is elevated at the mRNA and protein levels relative to normal B-cell subsets. E2A silencing in primary CLL cells leads to a significant increase in spontaneous apoptosis in both CD38(+) (aggressive) and CD38(-) (indolent) cases. Moreover, E2A knockdown synergizes with the immunomodulatory drug lenalidomide to reduce CLL viability. E2A is known to restrain the proliferation of primary B and T lymphocytes at multiple stages of maturation and we report that targeted E2A disruption increases the frequency of Ki-67(+) CLL cells in the absence of effects on de novo proliferation. At the molecular level, E2A siRNA-treated CLL cells display reduced expression of key genes associated with survival and cell cycling including p27, p21 and mcl-1, of which the former two are known E2A target genes. Thus, E2A, a key transcription factor associated with the B-cell activation profile, regulates apoptosis in CLL and may contribute to disease pathology.
Degeneration of the thymus and severe contraction of the T cell repertoire with aging suggest that immune homeostasis in old age could be mediated by distinct effectors. Therefore, receptors ...expressed on T cells as they undergo senescence in vitro, as well as those displayed by circulating T cells during normal chronologic aging, were examined. Monitoring of T cells driven to senescence showed de novo induction of CD56, the prototypic receptor of NK cells. Analysis of fresh T cells in peripheral blood showed an age-dependent induction of CD56. These unusual T cells expressed high levels of Bcl2, p16, and p53, and had limited, or completely lost, ability to undergo cell division, properties consistent with senescence. CD56 cross-linking without TCR ligation on CD56(+) T cells resulted in extensive protein phosphorylation, NF-kappaB activation, and Bax down-regulation. CD56 cross-linking was also sufficient to drive production of various humoral factors. These data suggest that the immunologic environment in old age is functionally distinct, rather than being a dysfunctional version of that seen at a young age. CD56(+) T cells are unique effectors capable of mediating TCR-independent immune cascades that could be harnessed to enhance protective immunity in the elderly.
CD28 is the quintessential costimulatory molecule expressed on CD4+ and CD8+ T cells. During chronic infections and the normal aging process, CD28 expression is lost, compromising the functional ...activity of T cells. CD28 loss is promoted by replicative stress, particularly in the presence of tumor necrosis factor–α, owing to an inoperative CD28 initiator element. It is currently unknown whether CD28 loss is irreversible. The present study examined cytokines for their ability to reinduce CD28 expression. CD4+CD28null T cells constitutively expressed interleukin-12 (IL-12) α and β receptors, which were functional and allowed for the up-regulation of the signal transducer and activator of transcription–4 (STAT-4)–dependent gene CD161. Costimulation of the T-cell and IL-12 receptors induced the transcription of CD28 in approximately 50% of CD4+CD28null T-cell clones and lines. IL-12 by itself did not restore CD28 expression. Up-regulation of CD28 after IL-12 exposure correlated with the reassembly of the CD28–initiator protein complex. The re-expressed CD28 was functional and restored the ability of CD4+CD28null T cells to express CD25 and CD40 ligand. Our data suggest that IL-12 may, in part, functionally rescue senescent CD4+ T cells.
CD28null T cells are the most consistent biological indicator of the aging immune system in humans and are predictors of immunoincompetence in the elderly. The loss of CD28 is the result of an ...inoperative transcriptional initiator (INR), which consists of two nonoverlapping α and β motifs that have distinct protein binding profiles but function as a unit. In CD28null T cells, there is a coordinate loss of α-/β-bound complexes, hence the αβ-INR is inactive. In the present work therefore, studies were conducted to identify the components of such complexes that may account for thetrans-activation of the αβ-INR. By affinity chromatography and tandem mass spectrometry, two proteins, namely, nucleolin and the A isoform of heterogeneous nuclear ribonucleoprotein-D0 (hnRNP-D0A), were identified to be among the key components of the site α complex. In DNA binding assays, specific antibodies indicated their antigenic presence in α-bound complexes. Transcription assays showed that they are both required in thetrans-activation of αβ-INR-driven DNA templates. Because CD28 is T cell-restricted, and nucleolin and hnRNP-D0A are ubiquitous proteins, these results support the notion that cell-specific functions can be regulated by commonly expressed proteins. The present data also provide evidence for INR-regulated transcription that is independent of the known components of the basal transcription complex.
Aging in the immune system is characterized by the contraction of the lymphocyte repertoire, exemplified by long-lived oligoclonal T cells that pervade the peripheral circulation. T-cell receptor ...(TCR) repertoire contraction likely explains the decline in immunity with chronological age as evidenced by the increased morbidity and mortality to common and new infections, and the low rates of protective responses to vaccination in the elderly. Interestingly, in vitro senescence models and cross sectional ex vivo studies have consistently demonstrated that senescent (or pre-senescent) T cells and T cells of the aged express unusually high densities of receptors that are normally found on natural killer (NK) cells, the killer cell immunoglobulin-like receptors (KIR) being the most diverse NK receptors (NKR). Molecular studies also show that T cells are programmed to express NKRs/KIRs, and T-cell clonal lineages express a variety of NKRs towards the end stages of their replicative lifespan. We propose that NKR/KIR induction in aging T cells is an adaptational diversification of the immune repertoire. We suggest that NKR/KIR expression in oligoclonal senescent and pre-senescent T cells is a compensatory adaptation to maintain immune competence despite the overall contraction in TCR diversity with aging. NKRs comprise a diverse superfamily of receptors. Mounting evidence for NKR/KIR signaling pathways in T cells divergent from those seen in NK cells indicate that senescent NKR
+T cells are unique immune effectors. We suggest that appreciation of the functional diversity of these unusual NK-like T cells is central to the creative development of new strategies to enhance protective immunity in the aged.
The costimulatory molecule CD28 has a restricted tissue distribution and is expressed on T cells and some plasmacytoma cells. Although CD28 is constitutively expressed, its expression is transiently ...down-regulated following T cell activation and declines progressively with in vitro senescence. In vivo, CD8+ T cells and, less frequently, CD4+ T cells may completely lose CD28 surface expression during chronic infections and with aging. This correlates with changes of nuclear protein-binding activities to two motifs, site alpha and beta, within the CD28 minimal promoter. Both alpha- and beta-bound complexes are found only in lymphoid tissues, in CD28+ T cells, and in some transformed B cells. These complexes are coordinately expressed except during replicative senescence, which is characterized by the down-modulation of site beta- but not site alpha-binding activities. In contrast, T cell activation induces a parallel decline in both site alpha- and beta-binding activities. CD4+ and CD8+ T cells differ in their beta-binding profiles, which may explain the more pronounced down-regulation of CD28 in senescent CD8+ T cells. In vivo expanded CD4+CD28null and CD8+CD28null T cells uniformly lack alpha- and beta-bound complexes, resembling the pattern seen in chronically activated cells and not of senescent cells.
Studies comparing chronologically "young" versus "old" humans document age-related decline of classical immunological functions. However, older adults aged ≥65 years have very heterogeneous health ...phenotypes. A significant number of them are functionally independent and are surviving well into their 8(th)-11(th) decade life, observations indicating that aging or old age is not synonymous with immune incompetence. While there are dramatic age-related changes in the immune system, not all of these changes may be considered detrimental. Here, we review evidences for novel immunologic processes that become elaborated with advancing age that complement preserved classical immune functions and promote immune homeostasis later in life. We propose that elaboration such of late life immunologic properties is indicative of beneficial immune remodeling that is an integral component of successful aging, an emerging physiologic construct associated with similar age-related physiologic adaptations underlying maintenance of physical and cognitive function. We suggest that a systems approach integrating immune, physical, and cognitive functions, rather than a strict immunodeficiency-minded approach, will be key towards innovations in clinical interventions to better promote protective immunity and functional independence among the elderly.
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