Leukocyte function in the aging immune system.

Aging is associated with a progressive dysregulation of immune responses. Whether these changes are solely responsible for the observed increased mortality and morbidity amongst the elderly is uncertain. Recent advances have highlighted the age-associated changes that occur beyond T and B lymphocytes. Additionally, multiple human and animal studies have identified a relationship between chronic low-grade inflammation and geriatric syndromes, such as frailty, suggesting that the phenomenon of "inflamm-aging" may provide a rationale for the increased vulnerability to chronic inflammatory diseases in older adults. In the present review, we broadly summarize our current understanding of age-dependent changes in leukocyte function and their contribution to aging-related disease processes.

Targeting MARCO can lead to enhanced dendritic cell motility and anti-melanoma activity.

We reported that murine tumor lysate-pulsed dendritic cells (TP-DC) could elicit tumor-specific CD4(+) and CD8(+) T cells in vitro and in vivo. In some limited cases, TP-DC treatments in vivo could also result in regression of established subcutaneous tumors and lung metastases. By gene array analysis, we reported a high level of expression of a novel member of the cell surface class A scavenger receptor family, MARCO, by murine TP-DC compared to unpulsed DC. MARCO is thought to play an important role in the immune response by mediating binding and phagocytosis, but also in the formation of lamellipodia-like structures and dendritic processes. We have now examined the biologic and therapeutic implications of MARCO expressed by TP-DC. In vitro exposure of TP-DC to a monoclonal anti-MARCO antibody resulted in a morphologic change of rounding with disappearance of dendritic-like processes. TP-DC remained viable after anti-MARCO antibody treatment; had little, if any, change in production of IL-10, IL-12p70 and TNF-alpha; but demonstrated enhanced migratory capacity in a microchemotaxis assay. The use of a selective inhibitor showed MARCO expression to be linked to the p38 mitogen-activated protein kinase (MAPK) pathway. In vivo, anti-MARCO antibody treated TP-DC showed better trafficking from the skin injection site to lymph node, enhanced generation of tumor-reactive IFN-gamma producing T cells, and improved therapeutic efficacy against B16 melanoma. These results, coupled with our finding that human monocyte-derived DC also express MARCO, could have important implications to human clinical DC vaccine trials.

The role of epigenetics in aging and autoimmunity.

The decline in immunocompetence with age is accompanied by the increase in the incidence of autoimmune diseases. Aging of the immune system, or immunosenescence, is characterized by a decline of both T and B cell function, and paradoxically the presence of low-grade chronic inflammation. There is growing evidence that epigenetics, the study of inherited changes in gene expression that are not encoded by the DNA sequence itself, changes with aging. Interestingly, emerging evidence suggests a key role for epigenetics in human pathologies, including inflammatory and neoplastic disorders. Here, we will review the potential mechanisms that contribute to the increase in autoimmune responses in aging. In particular, we will discuss how epigenetic alterations, especially DNA methylation and histone acetylation, are accumulated during aging and how these events contribute to autoimmunity risk.

Mechanisms of murine dendritic cell antitumor dysfunction in aging.

Effective cancer immunotherapy depends on the body's ability to generate tumor antigen-presenting cells and tumor-reactive effector lymphocytes. As the most potent antigen presenting cells (APCs), dendritic cells (DCs) are capable of sensitizing T cells to new and recall antigens. Clinical trials of antigen-pulsed autologous DCs have been conducted in patients with a number of hematological and solid cancers, including malignant melanoma, lymphoma, myeloma, and non-small cell lung cancer. These studies suggest that antigen-loaded DC vaccination is a potentially safe and effective cancer therapy. However, the clinical results have been variable. Since the elderly are preferentially affected by diseases targeted by DC-directed immunotherapy, it is quite striking that few studies to date have focused on the effect of aging on DC function, a key aspect of optimal immunotherapy design in an aging population. In the present paper, we will discuss the consequences of aging on murine bone marrow-derived DC function and their use in cancer immunotherapy.

Impaired dendritic cell function in aging leads to defective antitumor immunity.

We recently reported that bone marrow-derived dendritic cells (DC) from aged miced are less effective than their young counterparts in inducing the regression of B16-ovalbumin (OVA) melanomas. To examine the underlying mechanisms, we investigated the effect of aging on DC tumor antigen presentation and migration. Although aging does not affect the ability of DCs to present OVA peptide((257-264)), DCs from aged mice are less efficient than those from young mice in stimulating OVA-specific T cells in vitro. Phenotypic analysis revealed a selective decrease in DC-specific/intracellular adhesion molecule type-3-grabbing nonintegrin (DC-SIGN) level in aged DCs. Adoptive transfer experiments showed defective in vivo DC trafficking in aging. This correlates with impaired in vitro migration and defective CCR7 signaling in response to CCL21 in aged DCs. Interestingly, vaccination of young mice using old OVA peptide((257-264))-pulsed DCs (OVA PP-DC) resulted in impaired activation of OVA-specific CD8(+) T cells in vivo. Effector functions of these T cells, as determined by IFN-gamma production and cytotoxic activity, were similar to those obtained from mice vaccinated with young OVA PP-DCs. A decreased influx of intratumor CD8(+) T cells was also observed. Importantly, although defective in vivo migration could be restored by increasing the number of old DCs injected, the aging defect in DC tumor surveillance and OVA-specific CD8(+) T-cell induction remained. Taken together, our findings suggest that defective T-cell stimulation contributes to the observed impaired DC tumor immunotherapeutic response in aging.

The effect of aging and caloric restriction on murine CD8+ T cell chemokine receptor gene expression.

BACKGROUND: The mechanism explaining the increased disease susceptibility in aging is not well understood. CD8+ T cells are crucial in anti-viral and anti-tumor responses. Although the chemokine system plays a critical role in CD8+ T cell function, very little is known about the relationship between aging and the T cell chemokine system. RESULTS: In this study we have examined the effect of aging on murine CD8+ T cell chemokine receptor gene expression. Freshly isolated splenic CD8+ T cells from old C57BL/6 mice were found to have higher CCR1, CCR2, CCR4, CCR5 and CXCR5, and lower CCR7 gene expression compared to their younger cohort. Anti-CD3/anti-CD28 stimulation elicited a similar robust chemokine receptor response from young and old CD8+ T cells. Western blot analyses confirmed elevated protein level of CCR4 and CCR5 in aged CD8+ T cells. Increases in T cell CCR1 and CCR5 expression also correlate to increased in vitro chemotaxis response to macrophage-inflammatory protein-1 alpha(MIP-1alpha). Finally, caloric restriction selectively prevents the loss of CD8+ T cell CCR7 gene expression in aging to the level that is seen in young CD8+ T cells. CONCLUSION: These findings are consistent with the notion that aging exists in a state of low grade pro-inflammatory environment. In addition, our results provide a potential mechanism for the reported aging-associated impaired T cell lymphoid homing and allograft response, and reduced survival in sepsis.

Effect of aging on bone marrow-derived murine CD11c+CD4-CD8alpha- dendritic cell function.

Dendritic cells (DCs) are actively used as cellular adjuvant in cancer immunotherapy. However, although DC immunotherapies primarily target the elderly population, little is known about the effect of aging on DC functions. Here, we compared the T-cell stimulation, cytokine production, and tumor surveillance functions of bone marrow-derived CD11c(+)CD4(-)CD8alpha(-) DCs of old and young C57BL/6 mice. Old immature bone marrow-derived CD4(-)CD8alpha(-) DCs (imDCs) were 4 times less effective than were young DCs in stimulating syngeneic CD4(+) T-cell proliferation. Old imDCs also have decreased DC-specific/intracellular adhesion molecule type 3-grabbing, nonintegrin (DC-SIGN) expression compared to young DCs. Interestingly, mice treated with the ovalbumin peptide-pulsed young DCs exhibited significantly greater tumor regression than with ovalbumin peptide-pulsed old DCs. Old terminally differentiated bone marrow-derived DCs (tDC) also have increased interleukin-10, but decreased interleukin-6 and tumor necrosis factor-alpha production. Taken together, these results have important implications in the clinical application of DC-based tumor immunotherapy in elderly persons.

Estrogen regulates CCR gene expression and function in T lymphocytes.

Estrogen has been implicated in the observed female bias in autoimmune diseases. However, the mechanisms behind this gender dimorphism are poorly defined. We have previously reported that in vivo T cell trafficking is gender- and estrogen-dependent. Chemokine receptors are critical determinants of T cell homing and immune response. In this study, we show that the female gender is associated with increased CD4(+) T cell CCR1-CCR5 gene and protein expression in mice. The increased CCR expression correlates with enhanced in vitro chemotaxis response to MIP-1beta (CCL4). In vivo treatment of young oophorectomized and postmenopausal female mice with 17beta-estradiol also increased CD4(+) T cell CCR expression. Finally, 17beta-estradiol enhances tyrosine phosphorylation in T cells stimulated with MIP-1alpha in a time-dependent manner. Our results indicate an important role of estrogen in determining T cell chemokine response that may help explain the increased susceptibility and severity of autoimmune diseases in females.