Carl Fortin

Signal transduction and functional changes in neutrophils with aging.

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first‐line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor‐driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.

Aging and innate immunity in the mouse: impact of intrinsic and extrinsic factors

Aging affects every innate immune cell, including changes in cell numbers and function. Defects in the function of some cells are intrinsic, whereas for other cells, defects are extrinsic and possibly the consequence of the complex interactions with other cell types or the environmental milieu that is altered with aging. Abnormal function contributes to worsened outcomes after injury or infection and leads to diseases observed in the elderly. Knowing the mechanisms responsible for the aberrant function of innate immune cells might lead to the development of therapeutic strategies designed to improve innate immunity in aged individuals. Herein, advances in the field of innate immunity and aging with a focus on neutrophils, macrophages and dendritic cells in laboratory animals are discussed.

Potential role of immunosenescence in cancer development

The incidence and prevalence of most cancers increase with age. The reasons for this may include tumor escape mechanisms and decreased immunosurveillance, but most are caused by the time required for carcinogenesis, according to most scientists. The immune system is a unique mechanism of defense against pathogens and possibly cancers; however, there is a body of evidence that the immune system of the aged is eroded, a phenomenon termed immunosenescence. There is a growing interest in immunosenescence and how it may contribute to the increased number of cancers with aging. Each arm of the immune system, innate and adaptive, is altered with aging, contributing to increased tumorigenesis. Understanding the contribution of immunosenescence to cancer development and progression may lead to better interventions for the elderly.

Impairment of SHP-1 down-regulation in the lipid rafts of human neutrophils under GM-CSF stimulation contributes to their age-related, altered functions

It has been shown that the functions and the rescue from apoptosis by proinflammatory mediators of polymorphonuclear leukocytes (PMN) tend to diminish with aging. Here, we investigated the role of protein tyrosine phosphatases (PTP), especially Src homology domain‐containing protein tyrosine phosphatase‐1 (SHP‐1), in the age‐related, altered PMN functions under granulocyte macrophage‐colony stimulating factor (GM‐CSF) stimulation. The inhibition of PTP suggested a differential effect of GM‐CSF on phosphatase activity in modulating PMN functions with aging. The down‐regulation of phosphatase activity of immunopurified SHP‐1 from lipid rafts of PMN of young donors was found significantly altered at 1 min of stimulation with aging. In young donors, SHP‐1 is displaced from lipid rafts at 1 min of stimulation, whereas in the elderly, SHP‐1 is constantly present. We assessed in PMN lipid rafts the phosphorylation of tyrosine and serine residues of SHP‐1, which regulates its activity. We observed an alteration in the phosphorylation of tyrosine and serine residues of SHP‐1 in PMN of elderly subjects, suggesting that GM‐CSF was unable to inhibit SHP‐1 activity by serine phosphorylation. GM‐CSF activates Lyn rapidly, and we found alterations in its activation and translocation to the lipid rafts with aging. We also demonstrate that SHP‐1 in the PMN of elderly is constantly recruited to Lyn, which cannot be relieved by GM‐CSF. In contrast, in the young, the resting recruitment could be relieved by GM‐CSF. Our results suggest an alteration of the SHP‐1 modulation by GM‐CSF in lipid rafts of PMN with aging. These alterations could contribute to the decreased GM‐CSF effects on PMN.

Cellular signaling in the aging immune system.

Causes for immunosenescence and inflamm-aging have to be established. Efficient function of the immune system requires homeostatic regulation from receptor recognition of antigenic challenge to cell responses and adaptation to its changing environment. It is reasonable to assume that one of the most important molecular causes of immunosenescence is alteration in the regulation of signaling pathways. Indeed, alterations in feed-forward and negative feedback (inhibitory) signaling have been highlighted in all cells involved in the immune response including short-lived (neutrophils) and long-lived (T lymphocytes) cells. These dysregulations tip the balance in favor of altered (less efficient) function of the immune system. In this review, we summarize our knowledge on signal transduction changes in the aging immune system and propose a unifying mechanism as one of the causes of immunosenescence. Modulation of these pathways with aging represents a major challenge to restore the immune response to functional levels.

Aging and neutrophils: there is still much to do.

Human neutrophils are activated by a wide array of compounds through their receptors. This elicits their classical functions, such as chemotaxis, phagocytosis, and the production of reactive oxygen species (ROS). Upon stimulation, neutrophils also produce lipid and immune mediators and can present antigen through the major histocompatibility complex I (MHC-I). The age-related impairment of the classical functions of neutrophils is well described, but experimental evidence showing alterations in the production of mediators and antigen presentation with aging are lacking. This review highlights the role of neutrophils in age-related pathologies such as Alzheimers disease, atherosclerosis, cancer, and autoimmune diseases. Furthermore, we discuss how aging potentially affects the production and release of mediators by human neutrophils in ways that may contribute to the development of these pathologies.

The role of the MAPK pathway alterations in GM-CSF modulated human neutrophil apoptosis with aging

BackgroundNeutrophils represent the first line of defence against aggressions. The programmed death of neutrophils is delayed by pro-inflammatory stimuli to ensure a proper resolution of the inflammation in time and place. The pro-inflammatory stimuli include granulocyte-macrophage colony-stimulating factor (GM-CSF). Recently, we have demonstrated that although neutrophils have an identical spontaneous apoptosis in elderly subjects compared to that in young subjects, the GM-CSF-induced delayed apoptosis is markedly diminished. The present study investigates whether an alteration of the GM-CSF stimulation of MAPKs play a role in the diminished rescue from apoptosis of PMN of elderly subjects.MethodsNeutrophils were separated from healthy young and elderly donors satisfying the SENIEUR protocol. Neutrophils were stimulated with GM-CSF and inhibitors of the MAPKinase pathway. Apoptosis commitment, phosphorylation of signaling molecules, caspase-3 activities as well as expression of pro- and anti-apoptotic molecules were performed in this study. Data were analyzed using Students two-tailed t-test for independent means. Significance was set for p ≤ 0.05 unless stated otherwise.ResultsIn this paper we present evidence that an alteration in the p42/p44 MAPK activation occurs in PMN of elderly subjects under GM-CSF stimulation and this plays a role in the decreased delay of apoptosis of PMN in elderly. We also show that p38 MAPK does not play a role in GM-CSF delayed apoptosis in PMN of any age-groups, while it participates to the spontaneous apoptosis. Our results also show that the alteration of the p42/p44 MAPK activation contributes to the inability of GM-CSF to decrease the caspase-3 activation in PMN of elderly subjects. Moreover, GM-CSF converts the pro-apoptotic phenotype to an anti-apoptotic phenotype by modulating the bcl-2 family members Bax and Bcl-xL in PMN of young subjects, while this does not occur in PMN of elderly. However, this modulation seems MAPK independent.ConclusionOur results show that the alteration of p42/p44 MAPK activation contributes to the GM-CSF induced decreased PMN rescue from apoptosis in elderly subjects. The modulation of MAPK activation in PMN of elderly subjects might help to restore the functionality of PMN with aging.

Sepsis, leukocytes, and nitric oxide (NO): an intricate affair.

Sepsis is exceedingly burdensome for hospital intensive care unit caregivers, and its incidence, as well as sepsis-related deaths, is increasing steadily. Sepsis is characterized by a robust increase in NO production throughout the organism that is driven by iNOS. Moreover, NO is an important factor in the development of septic shock and is synthesized by NOS, an enzyme expressed by a variety of cells, including vascular endothelium, macrophages, and neutrophils. However, the effects of NO on leukocyte functions, and the underlying mechanisms, are relatively unknown. Thus, the present review focuses on the effects of NO and its derivatives on cells of the immune system. Experimental evidences discussed herein show that NO induces posttranslational modifications of key proteins in targeted processes with the potential of deterring cellular physiology. Consequently, the manipulation of NO distribution in septic patients, used in conjunction with conventional treatments aimed at restoring normal immune functions, may represent a valuable therapeutic strategy.

Effects of aging on triggering receptor expressed on myeloid cells (TREM)‐1‐induced PMN functions

Triggering receptor expressed on myeloid cell‐1 (TREM‐1) is a recently described receptor that has many effects on polymorphonuclear neutrophil (PMN), as the engagement of this receptor on PMN can induce phagocytosis, respiratory burst and degranulation. We studied the effects of aging on TREM‐1 engagement in human PMN. PMN from elderly were found to have impaired response following TREM‐1 engagement. Notably they were not able to modulate the TREM‐1‐induced respiratory burst as PMN from young did. TREM‐1 engagement could not reverse PMN survival following incubation with LPS or GM‐CSF in the elderly whereas it did in the young. The phosphorylation of TREM‐1 signal transduction molecules was altered with aging. Finally, TREM‐1 engagement could not drive the recruitment of TREM‐1 in the lipid‐rafts of the elderly explaining in part the altered response. The observed alterations in TREM‐1 response are possibly an important contributing factor in the higher incidence of sepsis‐related deaths in the elderly population.

Autocrine role of endogenous interleukin-18 on inflammatory cytokine generation by human neutrophils

Neutrophils are key players of innate immunity and influence inflammatory and immune reactions through the production of numerous cyto‐kines. Interleukin‐18 (IL‐18) is known to stimulate several neutrophil responses, and recent evidence sug‐gests that neutrophils might represent a source of IL‐18. Here, we show that neutrophils constitutively produce both IL‐18 and its antagonist, IL‐18BP. Cell activation does not affect IL‐18BP release but leads to an increased gene expression and secretion of IL‐18, a process that depends on NF‐κB activation. Moreover, endogenous IL‐18 feeds back on the neutrophils to augment cytokine generation in lipopolysaccharide‐treated cells. Accordingly, exogenous IL‐18 can induce the gene expression and release of several inflamma‐tory cytokines in neutrophils, including its own expression. We finally report that IL‐18 activates the p38 MAPK, MEK/ERK, and PI3K/Akt pathways in neutro‐phils. The IKK cascade is also activated by IL‐18, resulting in IκB‐α degradation, NF‐κB activation, and RelA phosphorylation. Accordingly, these pathways contribute to the generation of inflammatory cytokines in IL‐18‐stimulated neutrophils. By contrast, the phos‐phorylation and DNA‐binding activity of various STAT proteins were not induced by IL‐18. Collectively, our results unveil new interactions between IL‐18 and neutro‐phils and further support a role for these cells in influencing both innate and adaptive immunity.—Fortin, C. F., Ear, T., McDonald, P. P. Autocrine role of endogenous interleukin‐18 on inflammatory cytokine generation by human neutrophils. FASEB J. 23, 194‐203 (2009)