Cellular basis of decreased immune responses to pneumococcal vaccines in aged mice

Age-related functional decline of human B cells

This study aimed to investigate the changes in B cell functional decline and antigen sensitization with aging using two Epstein Barr virus (EBV)-immortalized human B cell lines, one from a 22-year-old man (EBV-B young) and the other from a 65-year-old man (EBV-B old). The activity of senescence-associated β-galactosidase, a marker of cellular senescence, was enhanced in the EBV-B old cells compared with EBV-B young cells. Moreover, the levels of p16, p21, IL-6, TNF-α, and TGF-β1, which are senescence-associated secretary phenotypes, were also increased in EBV-B old cells. In vitro immunization of EBV-B cells with β-lactoglobulin further showed that EBV-B old cells had a reduced cell population of naïve B cells than that of EBV-B young cells. Furthermore, HLA-DR expression, which is important for antigen presentation, was decreased in the EBV-B old cells. Comparative microarray analysis between EBV-B young and old cells also showed decreased expression of antibody genes, such as those of the heavy chain and light chain (κ chain). These results suggest that cellular senescence and decreased gene expression are responsible, at least in part, for the decline in B cell function and antigen sensitization capacity with aging, which ultimately impairs the function of the acquired immune system.

Macrophage-fibroblast circuits in the spleen

Macrophages are an integral part of all organs in the body, where they contribute to immune surveillance, protection, and tissue-specific homeostatic functions. This is facilitated by so-called niches composed of macrophages and their surrounding stroma. These niches structurally anchor macrophages and provide them with survival factors and tissue-specific signals that imprint their functional identity. In turn, macrophages ensure appropriate functioning of the niches they reside in. Macrophages thus form reciprocal, mutually beneficial circuits with their cellular niches. In this review, we explore how this concept applies to the spleen, a large secondary lymphoid organ whose primary functions are to filter the blood and regulate immunity. We first outline the splenic micro-anatomy, the different populations of splenic fibroblasts and macrophages and their respective contribution to protection of and key physiological processes occurring in the spleen. We then discuss firmly established and potential cellular circuits formed by splenic macrophages and fibroblasts, with an emphasis on the molecular cues underlying their crosstalk and their relevance to splenic functionality. Lastly, we conclude by considering how these macrophage-fibroblast circuits might be impaired by aging, and how understanding these changes might help identify novel therapeutic avenues with the potential of restoring splenic functions in the elderly.

Immunomodulation by the Commensal Microbiome During Immune-Targeted Interventions: Focus on Cancer Immune Checkpoint Inhibitor Therapy and Vaccination

Emerging evidence in clinical and preclinical studies indicates that success of immunotherapies can be impacted by the state of the microbiome. Understanding the role of the microbiome during immune-targeted interventions could help us understand heterogeneity of treatment success, predict outcomes, and develop additional strategies to improve efficacy. In this review, we discuss key studies that reveal reciprocal interactions between the microbiome, the immune system, and the outcome of immune interventions. We focus on cancer immune checkpoint inhibitor treatment and vaccination as two crucial therapeutic areas with strong potential for immunomodulation by the microbiota. By juxtaposing studies across both therapeutic areas, we highlight three factors prominently involved in microbial immunomodulation: short-chain fatty acids, microbe-associate molecular patterns (MAMPs), and inflammatory cytokines. Continued interrogation of these models and pathways may reveal critical mechanistic synergies between the microbiome and the immune system, resulting in novel approaches designed to influence the efficacy of immune-targeted interventions.

Perspective: Should Vitamin E Recommendations for Older Adults Be Increased?

Current vitamin E requirements are uniformly applied across the population for those >14 y of age. However, aging is associated with alterations in cellular and physiologic functions, which are affected by vitamin E. Therefore, it is questionable whether vitamin E requirements can be uniformly applied to all adult age categories. With aging, there is dysregulation of the immune system in which there are decreased cell-mediated and pathogen defense responses coupled with an overactive, prolonged inflammatory state. Both animal and human studies in the aged suggest that intake above currently recommended levels of vitamin E may improve immune and inflammatory responses and be associated with a reduced risk of infectious disease. We review the evidence that was considered in establishing the current requirements for vitamin E and highlight data that should be considered in determining the vitamin E requirements in older adults, particularly focusing on the evidence suggesting a benefit of increased vitamin E intake on immune function and inflammatory processes and resistance to infection. The main objective of this Perspective is to initiate the discussion of whether the current Dietary Reference Intake for vitamin E should be increased for the older population. We make this suggestion on the basis of mechanistic studies showing biological plausibility, correction of a major cellular dysfunction in older adults, and strong evidence from several animal and a few human studies indicating a reduction in risk and morbidity from infections.

Pre-clinical efficacy and safety of experimental vaccines based on non-replicating vaccinia vectors against yellow fever

BACKGROUND

Currently existing yellow fever (YF) vaccines are based on the live attenuated yellow fever virus 17D strain (YFV-17D). Although, a good safety profile was historically attributed to the 17D vaccine, serious adverse events have been reported, making the development of a safer, more modern vaccine desirable.

METHODOLOGY/PRINCIPAL FINDINGS

A gene encoding the precursor of the membrane and envelope (prME) protein of the YFV-17D strain was inserted into the non-replicating modified vaccinia virus Ankara and into the D4R-defective vaccinia virus. Candidate vaccines based on the recombinant vaccinia viruses were assessed for immunogenicity and protection in a mouse model and compared to the commercial YFV-17D vaccine. The recombinant live vaccines induced γ-interferon-secreting CD4- and functionally active CD8-T cells, and conferred full protection against lethal challenge already after a single low immunization dose of 10(5) TCID(50). Surprisingly, pre-existing immunity against wild-type vaccinia virus did not negatively influence protection. Unlike the classical 17D vaccine, the vaccinia virus-based vaccines did not cause mortality following intracerebral administration in mice, demonstrating better safety profiles.

CONCLUSIONS/SIGNIFICANCE

The non-replicating recombinant YF candidate live vaccines induced a broad immune response after single dose administration, were effective even in the presence of a pre-existing immunity against vaccinia virus and demonstrated an excellent safety profile in mice.

SIRT1 links CIITA deacetylation to MHC II activation

Antigen-dependent stimulation of T cells plays a critical role in adaptive immunity and host defense. Activation of major histocompatibility complex II (MHC II) molecules, dictated by Class II transactivator (CIITA), is considered a pivotal step in this process. The mechanism underlying differential regulation of CIITA activity by the post-translational modification machinery (PTM) and its implications are not clearly appreciated. Here, we report that SIRT1, a type III deacetylase, interacts with and deacetylates CIITA. SIRT1 activation augments MHC II transcription by shielding CIITA from proteasomal degradation and promoting nuclear accumulation and target binding of CIITA. In contrast, depletion of SIRT1 upregulates CIITA acetylation and attenuates its activity. Nicotinamide phosphoribosyltransferase (NAMPT) that synthesizes NAD⁺ required for SIRT1 activation exerts similar effects on CIITA activity. Two different types of stress stimuli, hypobaric hypoxia and oxidized low-density lipoprotein (oxLDL), induce the acetylation of CIITA and suppress its activity by inhibiting the SIRT1 expression and activity. Thus, our data link SIRT1-mediated deacetylation of CIITA to MHC II transactivation in macrophages and highlight a novel strategy stress cues may employ to manipulate host adaptive immune system.

Role of phosphoinositide 3-kinase-Akt signaling pathway in the age-related cytokine dysregulation in splenic macrophages stimulated via TLR-2 or TLR-4 receptors

Age-associated defects in both B-lymphocytes and macrophages in elderly result in a reduction in the efficacy of vaccines to many Gram positive bacteria like Streptococcus pneumoniae. Splenic macrophages from aged mice have been shown to have a defect in production of pro-inflammatory cytokines (IL-6, IL-12, IL-1β, TNF-α) but exhibit increased production of IL-10 upon TLR-4 ligation. Here we showed that aged macrophages demonstrate similar cytokine dysregulation phenotype upon stimulation with TLR-2 ligands, or killed S. pneumoniae. We hypothesized that an age-associated increase in activity of phosphatidyl inositol 3-kinase (PI3K)-Akt signaling pathway may be playing a causal role in the age-associated cytokine dysregulation. We found that gene expression of both the regulatory (p85β) and the catalytic (p110δ) subunits of Class IA PI3K is higher in aged than in young splenic macrophages. The age-associated increase in the activity of PI3K was also demonstrated by an upregulation of P-Akt and its downstream target, glycogen synthase kinase-3 (GSK-3). Inhibition of PI3K enhanced induction of pro-inflammatory cytokines, by TLR-2/TLR-1, TLR-2/TLR-6 and TLR-4 ligands as well as heat killed S. pneumoniae (HKSP). Therefore, targeting PI3-Kinase could rescue cytokine dysregulation in aged macrophages and enhance the relevant pro-inflammatory cytokines needed to support B-cell activation and differentiation.

Preserved ex vivo inflammatory status and cytokine responses in naturally long-lived mice

Preserved immune cell function has been reported in mice that achieve extreme longevity. Since cytokines are major modulators of immune responses, we aimed to determine the levels of 21 cytokines secreted ex vivo by peritoneal leukocytes cultured under basal- and mitogen- (conconavalin A (ConA) and LPS) stimulated conditions in middle-aged (44 ± 4 weeks), old (69 ± 4 weeks), very old (92 ± 4 weeks), and extreme long-lived (125 ± 4 weeks) ICR (CD1) female mice. The secretion of cytokines was measured by multiplex luminometry. Increased basal levels of proinflammatory IL-1β, IL-6, IL-12 (p70), IFN-γ, and TNF-α were seen in the old and very old animals, accompanied by decreased IL-10. In contrast, the extreme long-lived mice maintained the overall cytokine profile of middle-aged mice, though the basal secretion of IL-2, IL-9, IL-10, IL-13, and IL-12 (p40) was raised. Under LPS- and/or ConA-stimulated conditions, leukocytes from old and very old animals showed a significantly impaired response with respect to secretion of Th1 cytokines IL-3, IL-12p70, IFN-γ, and TNF-α; Th2 cytokines IL-6, IL-4, IL-10, and IL-13; and the regulatory cytokines IL-2, IL-5, and IL-17. Extreme long-lived mice preserved the middle-aged-like cytokine profile, with the most striking effect seen for the IL-2 response to ConA, which was minimal in the old and very old mice but increased with respect to the middle-aged level in extreme long-lived mice. Chemokine responses in regard to KC, MCP-1, MIP1β, and RANTES were more variable, though similar secretion of LPS-induced KC and MCP-1 and ConA-induced MCP-1, MIP-1β, and RANTES was found in long-lived and middle-aged mice. Thus, extreme long-lived animals showed only a minimal inflammatory profile, much lower than the old and very old groups and also lower than the middle-aged, which is likely mediated by the increase of anti-inflammatory cytokines such as IL-10. This was coupled to a robust response to immune stimuli across an appropriated Th1/Th2 and regulatory cytokine secretion, which seems to be a factor contributing to the preserved immune response reported in very long-lived animals and thus to their extended longevity.

Age-related decline in immunity: implications for vaccine responsiveness

Aging is associated with declines in immune system function, or 'immunosenescence', leading to progressive deterioration in both innate and adaptive immunity. These changes contribute to the decreased response to vaccines seen in many older adults, and morbidity and mortality from infection. Infections (e.g., influenza, pneumonia and septicemia) appear among the top ten most-common causes of death in adults in the USA aged 55 years and older. As immunosenescence has gathered more attention in the scientific and healthcare communities, investigators have demonstrated more links between immunosenescent changes and morbidity and mortality related to infections and declining vaccine responses. This review summarizes the recent literature on age-dependent defects in adaptive and innate immunity, data linking these defects to poor vaccine response and morbidity and mortality, current recommendations for vaccinations and potential strategies to improve vaccine efficacy in older adults.

Aging and the dendritic cell system: implications for cancer

The immune system shows a decline in responsiveness to antigens both with aging, as well as in the presence of tumors. The malfunction of the immune system with age can be attributed to developmental and functional alterations in several cell populations. Previous studies have shown defects in humoral responses and abnormalities in T cell function in aged individuals, but have not distinguished between abnormalities in antigen presentation and intrinsic T cell or B cell defects in aged individuals. Dendritic cells (DC) play a pivotal role in regulating immune responses by presenting antigens to naïve T lymphocytes, modulating Th1/Th2/Th3/Treg balance, producing numerous regulatory cytokines and chemokines, and modifying survival of immune effectors. DC are receiving increased attention due to their involvement in the immunobiology of tolerance and autoimmunity, as well as their potential role as biological adjuvants in tumor vaccines. Recent advances in the molecular and cell biology of different DC populations allow for addressing the issue of DC and aging both in rodents and humans. Since DC play a crucial role in initiating and regulating immune responses, it is reasonable to hypothesize that they are directly involved in altered antitumor immunity in aging. However, the results of studies focusing on DC in the elderly are conflicting. The present review summarizes the available human and experimental animal data on quantitative and qualitative alterations of DC in aging and discusses the potential role of the DC system in the increased incidence of cancer in the elderly.

Murine [corrected] myeloid dendritic cell-dependent toll-like receptor immunity is preserved with aging

The immune response is the result of the interplay between innate and adaptive immunity, yet the impact of aging on this interaction is unclear. Addressing this fundamental question will be critical for the development of effective vaccines for the rapidly rising older subpopulation that manifests increased prevalence of malignancies and infections. Therefore, we undertook the current study to investigate whether aging impairs toll-like receptor (TLR) function in myeloid dendritic cells and whether this leads to reduced T-cell priming. Our results demonstrate that innate TLR immune priming function of myeloid bone marrow derived and splenic dendritic cells (DC) is preserved with aging using both allogeneic and infectious murine experimental systems. In contrast, aging impairs in vitro and in vivo intrinsic T-cell function. Therefore, our results demonstrate that myeloid DCs manifest preserved TLR-mediated immune responses with aging. However, aging critically impairs intrinsic adaptive T-cell function.

Defective microarchitecture of the spleen marginal zone and impaired response to a thymus-independent type 2 antigen in mice lacking scavenger receptors MARCO and SR-A

The macrophage scavenger receptor macrophage receptor with a collagenous structure (MARCO) is expressed in mice by the marginal zone macrophages of the spleen and by macrophages of the medullary cords of lymph nodes, as well as the peritoneal macrophages. MARCO is a relative of scavenger receptor A (SR-A), the more widely expressed prototypic member of the scavenger receptor family. In the present study, we found that genetic ablation of MARCO leads to changes in the organization of the splenic marginal zone, and causes a significant reduction in the size of the resident peritoneal macrophage population, possibly due to changes in adhesion and migration capacity. In mice lacking both MARCO and SR-A these effects are even more apparent. During ontogeny, the appearance and organization of the MARCO-expressing cells in the spleen precedes the appearance of other receptors on macrophages in the marginal zone, such as SIGNR1 and Siglec-1. In the absence of MARCO, a clear delay in the organization of the marginal zone was observed. Similar findings were seen when the reappearance of the various subsets from precursors was studied after depleting macrophages from the adult spleen by a liposome treatment. When challenged with a pneumococcal polysaccharide vaccine, a T-independent type 2 Ag for which an intact marginal zone is crucial, the knockout mice exhibited a clearly impaired response. These findings suggest that both MARCO and SR-A, in addition to being important scavenger receptors, could be involved in the positioning and differentiation of macrophages, possibly through interaction with endogenous ligands.

MacrophAging: a cellular and molecular review

Aging is associated with the deterioration of several physiological functions, which leads to aged-related pathologies and, ultimately, to death. The immune system is affected by aging, causing an increased susceptibility to infections and mortality, as well as a major incidence of immune diseases and cancer in the elderly. Because macrophages are an essential component of both innate and adaptive immunity, altered function of these phagocytic cells with aging may play a key role in immunosenescence. Here we summarize data about the effects of aging on macrophages and we discuss the molecular events that could be involved in this process.

Intrinsic versus environmental influences on T-cell responses in aging

A decline in T-cell responses and a switch to memory T-cell predominance occur with aging. We have used the T-cell receptor (TCR) transgenic mouse model to study age-associated changes in T-cell responses that are a consequence of shifts in subset representation versus changes intrinsic to T cells versus changes in the 'aged' microenvironment. We found that naive transgene-expressing (Tg(+)) CD4(+) T cells from aged mice respond to antigen with reduced interleukin-2 (IL-2) production, decreased cell expansion, and limited differentiation to effectors. Comparable to the characteristic accumulation of memory phenotype T cells in aged humans and conventional rodents, Tg(+) CD4(+) T cells from old OTII and 6.5 TCR transgenic mice acquire a memory phenotype without immunization and become hyporesponsive. The naive Tg(+) CD8(+) T cells from aged 2C mice expressed activation markers, produced IL-2, proliferated, and differentiated into cytotoxic T lymphocytes as efficiently as their young counterparts. Responses by adoptive transferred Tg(+) cells from young mice, immunized in young and old conventional hosts, indicated that the host age influences the onset of cell division, level of cell expansion, and number of cytokine-producing cells. Co-transfer of dendritic cells (DCs) from young and less so from aged conventional mice partially restored responses. Furthermore, DCs and T-cell migration to draining lymphoid organs was reduced due to deficiencies intrinsic to aged cells and the aged environment. Thus, alterations in T-cell responses in aging are attributable to intrinsic and environmental influences.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

The unresponsiveness of aged mice to polysaccharide antigens is a result of a defect in macrophage function

A reduction in macrophage (MPhi) function with aging makes mice less responsive to bacterial capsular polysaccharides, such as those present in the pneumococcal polysaccharide vaccine, a model of thymus independent (TI) antigen (Ag). Using trinitrophenol (TNP)-lipopolysaccharide (LPS) and TNP-Ficoll, two other well-studied TI Ag, we studied the mechanistic basis of reduced MPhi function in the aged. We show that aged mice are profoundly hyporesponsive to these TI Ag. As a result of a requirement for MPhi, highly purified B cells from young-adult mice do not respond to TI Ag. When purified, young B cells were immunized with TNP-Ficoll, the antibody production from those cultures reconstituted with MPhi from aged mice was significantly lower than that seen with young MPhi. Consequently, this unresponsiveness can be overcome by a mixture of interleukin (IL)-1beta and IL-6. Upon stimulation with LPS, in comparison with young MPhi, aged MPhi secreted reduced amounts of IL-6, tumor necrosis factor alpha, IL-1beta, and IL-12, cytokines necessary for B cells to respond to TI Ag. LPS also induced aged MPhi to produce an excess of IL-10. Neutralization of IL-10 enhanced the production of proinflamatory cytokines by MPhi upon LPS stimulation and also induced Ab production by aged splenocytes. Thus, the inability of aged MPhi to help the B cell response appears to be caused by an excess of IL-10. As aged MPhi have a reduced number of cells expressing Toll-like receptor 4 and CD14, the imbalance in cytokine production might be partly a result of fewer cells expressing key components of the LPS receptor complex.

A murine model for the study of immune memory in response to pneumococcal conjugate vaccination

We developed a murine model for assessment of immunological memory and antibody-induced protection to nasopharyngeal (NP) challenges. BALB/c female mice (n = 10 mice per study parameter) were immunized with two priming doses of the licensed 7-valent pneumococcal (Pnc) conjugate vaccine and immune responses [antibody immunoglobulin G (IgG) levels, avidity and opsonophagocytic activity] were monitored for 26 weeks until IgG levels decreased to nearly baseline. A booster dose of either 2 microg conjugate or 5 microg polysaccharide vaccine was given at week 26. The ability of these two treatments to recall immune memory established by the conjugate vaccine was determined for types 4 and 14 for up to 63 days post-booster. The ability of challenge with pneumococcal type 14 to recall the immune response was also evaluated, as well as, the number of antibody secreting cells (ASC) specific to polysaccharide (Ps) 4, 6B, and 14. A higher dose of conjugate vaccine (2 microg) was necessary to elicit a significant increase in IgG levels after priming with one dose. Priming with lower doses (0.5 and 1.0 microg) only elicited modest increases in IgG levels. Recall of the immune response was found with either conjugate or Ps vaccines. NP challenge with type 14 at week 26 did not recall the immune response, although reduction in NP Pnc load was seen post-primary immunization at 5, 10 and 26 weeks. ASCs were detected in response to either conjugate or Ps booster doses. This model allows for the screening and determination of potential alternative vaccination regimens and the study of immunological markers of memory following Pnc vaccination.

Defective macrophage function in neonates and its impact on unresponsiveness of neonates to polysaccharide antigens

Neonates do not respond to thymus-independent (TI) antigens (Ag), making them vulnerable to infection with encapsulated bacteria. The antibody (Ab) response of adult and neonatal B cells to TI Ag requires certain cytokines, which are provided by T cells or macrophages (MPhi). Lipopolysaccharide (LPS) failed to induce neonatal MPhi to produce interleukin (IL)-1beta and tumor necrosis factor alpha (TNF-alpha) mRNA and to secrete IL-1beta, IL-12, and TNF-alpha. However, LPS induced neonates to secrete some IL-6 and three- to fivefold more IL-10 than adults. Accordingly, adding adult but not neonatal MPhi could restore the response of purified adult B cells to trinitrophenol (TNP)-LPS, a TI Ag. Increased IL-10 is causally related to decreased IL-1beta and IL-6 production, as IL-10(-/-) neonatal MPhi responded to LPS by secreting more IL-1beta and IL-6 than wild-type (WT) neonatal MPhi. When cultures were supplemented with a neutralizing Ab to IL-10, WT neonatal MPhi secreted increased amounts of IL-6 and allowed neonatal MPhi to promote adult B cells to mount an Ab response against TNP-LPS. Thus, neonates do not respond to TI Ag as a result of the inability of neonatal MPhi to secrete cytokines, such as IL-1beta and IL-6, probably as a result of an excess production of IL-10. This dysregulated cytokine secretion by neonatal MPhi may be a result of a reduction in expression of Toll-like receptor-2 (TLR-2) and TLR-4 and CD14.

Follicular dendritic cells in aging, a "bottle-neck" in the humoral immune response

Senescence leads to the appearance of atrophic follicular dendritic cells (FDCs) that trap and retain little immune complexes (IC), generate few memory B cells, and induce a reduced number of germinal centers (GC). Deficiencies in antibody responses to T cell dependent exogenous antigens such as pneumonia and influenza vaccines may reflect intrinsic FDC defects or altered FDC-B cell interactions. We recently studied antigen handling capacity and co-stimulatory activity of old FDCs and determined age-related changes in the expression or function of FcgammaRII or CR1 and 2 on FDCs. Here, we present an overview of FDC function in recall responses with known deficiencies in FDCs and GC development. Then, we review our recent work on aged FDCs and discuss age-related changes in molecular interactions between FDCs and B cells. We also discuss the causes underlying the impaired humoral immune response with respect to age-related molecular changes in FDC and B cell interactions. In vitro evidence suggests that FcgammaRII on aged FDCs is regulated abnormally and this in turn might cause the development of a defective FDC-network (reticulum) that retains few ICs, promotes ITIM signaling, prevents B cell proliferation and GC formation, and antibody production.

Proteins and their derived peptides as carriers in a conjugate vaccine for Streptococcus pneumoniae: self-heat shock protein 60 and tetanus toxoid

We induced T cell help for vaccination against Streptococcus pneumoniae (Pn) using self and foreign peptides and their source proteins conjugated to the capsular polysaccharide (CPS) of type 4 Pn; the carriers were self-heat shock protein 60 (HSP60) and tetanus toxoid (TT). We measured the production of IgG Abs to the CPS and the carriers, and tested resistance to challenge with highly lethal amounts of Pn injected i.p. (LD(50) x 10(3)-10(6)). We now report that vaccination protects old and young mice from bacterial challenge; however, there were significant differences in vaccine efficacy based on the carrier. Self-HSP60 peptide p458m was more effective than the whole HSP60 molecule and was equally effective compared with TT. Both p458m and TT were more protective than the TT-derived peptide p30 after a single vaccination. However, peptide p30 was effective in more MHC genotypes than was p458m. Unlike other vaccines, protection conferred by p458m was not related to the amount of anti-CPS Ab: mice that produced very little Ab were still protected from highly lethal doses of bacteria (LD(50) x 10(5)-10(6)). Furthermore, unlike the other carriers, there was no Ab response to the p458m carrier. Thus, peptides, self as well as foreign, can provide T cell help that differs functionally from that provided by the whole parent protein.

Problems and solutions to the development of vaccines in the elderly

Scientists involved in vaccine research and development face the challenge of protecting the ever-increasing elderly population from a broad spectrum of infectious diseases. The optimal vaccine-induced immune response to confer protection is undefined for many pathogens, and the field of vaccine research is undergoing a gradual shift from the original focus on humoral immunity to a focus that incorporates cellular and innate immune components. The age-related changes in various aspects of immune function, including an increase in a population of T cells that shows signs of replicative senescence, underscore the need to enhance research aimed at designing vaccines to meet the unique requirements of the elderly population.

Cutting edge: impaired Toll-like receptor expression and function in aging

Toll-like receptors (TLR) are pattern recognition receptors that recognize conserved molecular patterns on microbes and link innate and adaptive immune systems. We investigated whether the enhanced susceptibility to bacterial, yeast, and viral infections and poor adaptive immune responses in aging are a result of diminished expression and function of TLRs. We examined the expression and function of all murine TLRs on macrophages from young and aged mice. Both splenic and activated peritoneal macrophages from aged mice expressed significantly lower levels of all TLRs. Furthermore, macrophages from aged mice secreted significantly lower levels of IL-6 and TNF-alpha when stimulated with known ligands for TLR1 and 2, 2 and 6,TLR3, TLR4, TLR5, and TLR9 when compared with those from young mice. These results support the concept that increased susceptibility to infections and poor adaptive immune responses in aging may be due to the decline in TLR expression and function.

Old mice express a transient early resistance to pulmonary tuberculosis that is mediated by CD8 T cells

During the natural aging process the immune system undergoes many alterations. In particular, both the CD4 and CD8 T-cell compartments become compromised, and these changes have serious implications for the capacity of the elderly to control infection. As a result, the elderly are more susceptible to many infectious diseases, including primary infection and reactivation of latent infections. In this study we addressed the capacity of old mice to control an infection with Mycobacterium tuberculosis and to characterize the mechanism by which old mice, paradoxically, can express a transient early resistance to infection. This resistance was shown to be associated with the presence of CD8 T cells within the lungs that were capable of secreting gamma interferon, as illustrated by the demonstration that early resistance was lost in aged CD8 gene-disrupted mice. These studies therefore show that, despite a documented decline in general CD8 T-cell responsiveness in the elderly, a subset of CD8 T cells is an important early mediator of protection in the lungs of old mice that have been infected with M. tuberculosis.

Phenotype, antigen-presenting capacity, and migration of antigen-presenting cells in young and old age

In the present paper, we investigated whether the phenotype, the antigen-presenting capacity, and the migration of antigen-presenting cells (APCs), are affected by the aging process. APCs were obtained incubating peritoneal monocyte-macrophage cells with granulocyte-macrophage colony-stimulating factor (GM-CSF) (immature APCs) or GM-CSF and IFNgamma (mature APCs). Phenotypically, after 8 days incubation, APCs cultures were composed of CD11c and Mac-3 cells, with a similar representation, both in young and old mice. The absolute number and the expression of MHC I and II, CD80, and CD86 both on immature and mature APCs were not significantly different in young and old mice. APCs from old mice induced similar lymphocyte proliferative responses but lower lymphocyte cytotoxicity and a reduced number of CD8(+) T cells producing IFNgamma in comparison with APCs from young animals. Lymphocyte responses were antigen-specific, since TS/A pulsed APCs induced lymphocyte cytotoxicity against TS/A but not against syngeneic TUBO tumor cells. The low expression of the mRNA for the migratory CCR7 chemokine receptor present in immature APCs from old mice was greatly increased in mature APCs up to the levels found in APCs from young animals. The in vivo migration of APCs was higher in old than in young mice. These results demonstrate that some alterations in APCs function are present in aging, suggesting that an increased migratory capacity of old APCs may be required to balance their reduced antigen presentation to cytotoxic lymphocytes.

A novel approach to study variable heavy chain gene usage in response to the capsular polysaccharide of Neisseria meningitidis serogroup C

The molecular mechanisms involved in the relatively poor immune response in the elderly are not clearly understood. Qualitative aspects of the immune response could be a possible explanation for the differential response to T-independent antigens in young adults and elderly. This study is directed towards elucidating the differential usage of variable heavy chain by young adult and elderly derived sequences in response to the capsular polysaccharide of Neisseria meningitidis serogroup C. We currently report findings of a preliminary study designed to test the feasibility of a novel approach to isolate antigen-specific B cells. Paramagnetic beads coated with an anti-idiotypic antibody, which mimics the capsular polysaccharide of N. meningitidis serogroup C, were used to select B cells. Analysis of the gene usage data indicates some unexpected differences in the use of variable chain heavy chain in the case of young adult versus elderly sequences. The elderly derived sequences use a more diverse array of V(H) gene families in contrast to the young adult sequences, where the V(H) gene family usage is restricted. Nearly half the young adult sequences utilize V(H)3-15 germline sequence while only 25% of the elderly sequences use this germline sequence. There were interesting differences in the types of JH chain and the composition and length of CDR3 utilized by the two groups. Together, these significant differences may contribute towards the poor immune response to T-independent antigens in the elderly. These data validate the techniques used for these studies and suggest that it is pertinent to use this approach towards future investigations to elucidate gene usage in response to an antigen.

Early antigen-specific response by naive CD8 T cells is not altered with aging

Both a dramatic decline in CD8 responses and a switch to memory T cell predominance occur with aging. The extent to which the loss of responsiveness is the consequence of the accumulation of more differentiated vs intrinsically defective T cells (or both) has been unclear. Using similar conditions of Ag stimulation, we have examined the responses generated by CD8(+) cells isolated from aged TCR transgenic mice. We found that the naive transgene(+) CD8(+) cells from aged 2C mice expressed activation markers, produced IL-2, proliferated, and differentiated into cytotoxic T cells as efficiently as their young counterparts. The extent of responsiveness and the level of the responses were comparable in both age groups regardless of the stimulatory conditions used, i.e., partial costimulation/adhesion molecule expression on APCs, or presentation of lower affinity peptide or diminished peptide concentrations. By day 4 after Ag stimulation, no significant age-related differences were observed in the number of effector cells generated nor in the levels of secreted IL-2 or IFN-gamma. Upon restimulation of effector cells, IL-2 secretion and to a lesser extent TNF-alpha expression, but not IFN-gamma secretion, were diminished with age. These findings suggest that age-associated alterations in naive CD8 cell function are not found after primary stimulation, but may become apparent upon restimulation.

The frail elderly: role of dendritic cells in the susceptibility of infection

The decline in immunity in the elderly has largely been attributed to impairment of T cell mechanisms. This seems reasonable since the thymus involutes with age, so that the number of naïve cells to respond to new foreign antigens also declines. However, little is known about how aging affects antigen-presenting cells (APC) that are responsible for the initiation and outcome of effector T cell immune responses. This review focuses on the age-related alterations of a key APC, the dendritic cell (DC). Recent findings suggest that interleukin-10, a key cytokine that can suppress cell mediated immunity and maturation of DC subsets, is elevated in the very healthy elderly. However, production of IL-12, required for the initiation of T cell immune responses, declines in frail elderly along with DC antigen presenting function. These findings suggest that shifts in IL-10 and IL-12 may not only directly influence immune response but may also alter the balance and maturation of DC subsets. Finally, study of immunologic differences between the very healthy and frail elderly may reveal important changes in DC function and regulation influenced by age and/or environment (disease, nutrition, medications, etc.).

Chronological ageing and photoageing of dendritic cells

Ageing involves the whole organism, including the immune system. Age-dependent alterations of immune functions are located in both the adaptive and innate parts of the immune system. The most important cell type of the innate immune system are the dendritic cells, because their capacity to induce primary immune responses via professional antigen presentation is crucial for the initiation of the adaptive immune response. Evidence exists that dendritic cells of the systemic immune system, represented by lymph-node and blood-derived dendritic cells, as well as of local immunity, represented by Langerhans cells of the skin, participate in ageing processes. In animal models of older mice, dendritic cells of lymph nodes show degenerative characteristics with decreased adhesion molecule expression, less dendrite formation, and reduced antigen trapping capacity, which together imply disruption of functional activity. In contrast, dendritic cells generated from peripheral blood of elderly people were not impaired in their capacity to induce T-cell responses. Together, these findings indicate that in old individuals in vivo dendritic cells of the systemic immune system are reduced in their functional capacity to stimulate immune responses, whereas in vitro generated dendritic cells are fully functional, and therefore might be used in therapeutic approaches to treat age-associated malfunctions of the immune system. Thus far, only morphological descriptions about age-associated changes of dendritic cells (in particular the Langerhans cells) of the skin exist. In the skin, effects of naturally occurring ageing have to be differentiated from UV-radiation-induced ageing processes. The hallmark of Langerhans cell changes in natural as well as UV-induced skin ageing is their reduction in cell number within the epidermis. In addition, they show an atrophic morphology with less dendrites, and less Birbeck granules. It is assumed that these morphological changes are associated with loss of dendritic cell functions, and that this contributes to age-associated development of skin cancer. Therapeutic strategies against natural and UV-induced skin ageing should include a reduction of these changes of Langerhans cells in order to strengthen the immunological functions of the body's outer surface.

Immunohistochemical analysis of ageing human B and T cell populations reveals an age-related decline of CD8 T cells in spleen but not gut-associated lymphoid tissue (GALT)

It is thought that senescence of the immune system is responsible, at least in part, for many health problems associated with ageing. Previous studies on changes in lymphocyte composition have used flow cytometry to study peripheral blood lymphocytes (PBL's), or cells isolated from rodent tissue, and have yielded conflicting results. We have used immunohistochemistry to determine whether the B and T cells in human tissue from spleen and gut are affected by age. Areas of germinal centre, mantle zone and marginal zone of B cell follicles were measured. In addition, CD4 and CD8 T cells in T cell areas and in B cell follicles were counted. We observed a striking age-related decrease in the proportion of CD8+ T cells in the T cell zones of the spleen. This decrease was not apparent in the T cell population that occupies splenic B cell areas, or in GALT. Further differences, in CD4+ cells, were seen between T cell populations in the T cell zones and those in B cell areas. These findings highlight differences between lymphocyte populations in different lymphoid tissues, and different compartments within each tissue, which may be of importance in future studies of the ageing immune system.

Efficacy of cancer gene therapy in aging: adenocarcinoma cells engineered to release IL-2 are rejected but do not induce tumor specific immune memory in old mice

Numerous studies have demonstrated the efficacy of cytokine gene-engineered tumor cells to induce tumor rejection and specific memory acquisition into syngeneic immunocompetent mice by activation of host-dependent antitumor responses. A progressive immune dysfunction, mainly involving thymus-dependent specific immunity, occurs during aging. In this study we evaluated whether the injection of IL-2 gene-transfected tumor cells in old mice causes an immune activation which results in tumor rejection and induction of specific immune memory as occurs in young animals. Young and old mice were inoculated with syngeneic parental mammary adenocarcinoma cells (TS/A p.c.) or with TS/A cells engineered to release IL-2 (TS/A-IL2). Three clones of TS/A-IL-2 cells were used producing low (30 U, B1.30), intermediate (3600 U, B6.3600), or high (6000 U, B4.6000) IL-2. While the B1.30 clone grew in 100% of mice, the B6.3600 and B4.6000 clones were promptly rejected in both young and old animals. In young mice, rejection was associated with a large neutrophil and macrophage infiltration, with a minor number of CD4+ and CD8+ lymphocytes. In old mice, neutrophils and macrophages were the main cells involved in tumor rejection whereas both CD4+ and CD8+ lymphocytes were scarcely present in tumoral infiltrate. A lower number of apoptotic tumor cells was found in TS/A-IL2-challenged old mice in comparison with young animals. To test whether the injection of TS/A-IL2 cells induced a specific immune memory, mice with no tumors after the challenge with B6.3600 and B4.6000 clones received a lethal challenge of TS/A p.c. 90% and 30% of young mice previously injected with B4.6000 or B6.3600 clones, respectively, rejected TS/A p.c. In old mice, B4.6000 cells did not confer protection, whereas only 10% of mice which received B6.3600 cells were able to reject TS/A p.c. Neither the graft of a young thymus or the adoptive transfer of young T lymphocytes to old mice induced specific immune memory for TS/A p.c. in old animals. These data suggest the necessity to refine antitumor vaccination procedures in aging.

CpG oligodeoxynucleotides overcome the unresponsiveness of neonatal B cells to stimulation with the thymus-independent stimuli anti-IgM and TNP-Ficoll

Neonates are very vulnerable to pathogenic encapsulated bacteria due to their inability to mount an antibody response to capsular polysaccharides, which are thymus-independent type 2 (TI-2) antigens (Ag). Oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides induced neonatal B cells to proliferate to anti-IgM, a TI-2 stimulus. CpG ODN inhibited the spontaneous and B cell receptor-mediated apoptosis of neonatal B cells and reduced the amount of the pro-apoptotic Bcl-xS, strongly correlated with anti-IgM-induced apoptosis of neonatal B cells. CpG ODN protected neonatal B cells from apoptosis by down-regulation of the Bcl-xS protein. Neonatal B cells underwent polyclonal differentiation upon stimulation with CpG ODN, but unlike in adult B cells, this was not preceded by IL-6 secretion. CpG ODN stimulated neonatal B cells to mount an Ag-specific antibody response to TNP-Ficoll, another TI-2 Ag. Thus CpG ODN could provide a novel approach to induce the immune system in neonates to respond to harmful encapsulated bacteria.

Neonatal Murine B Lymphocytes Respond to Polysaccharide Antigens in the Presence of IL-1 and IL-6

Unlike adults, neonates are unable to respond to polysaccharide Ags, making them especially vulnerable to pathogenic encapsulated bacteria. Since the Ab response to polysaccharides in adult mice requires certain cytokines, it was hypothesized that neonatal murine B cells may be competent to respond to such Ags, but may fail to do so due to a deficiency of cytokines. Neonatal splenocyte cultures, which were otherwise unresponsive to trinitrophenyl (TNP)-Ficoll, a haptenated polysaccharide Ag, mounted an adult-like Ab response when supplemented with IL-1. However, IL-1 failed to induce such a response to TNP-Ficoll when purified B cells were used instead. Although IL-6 alone did not induce a response in whole spleen cells or purified B cells from neonates, it synergized with IL-1 in inducing purified neonatal B cells to respond to TNP-Ficoll. The avidity of the cytokine-induced neonatal anti-TNP Abs was comparable to that of Abs made by adult splenocyte cultures. One effect of IL-1 may be at the level of clonal expansion, since it induced neonatal B cells to proliferate in response to anti-IgM, which was further enhanced by IL-6. The spontaneous secretion of IL-1 by neonatal splenocytes was below the detection limit, while adult splenocytes secreted 30.8 ± 5.2 U/ml, which is of the same order of magnitude as what was required to stimulate neonatal B cells to respond to TNP-Ficoll. Thus, the neonatal unresponsiveness to polysaccharide Ags could be due to the inability of a non-B cell population resident in the neonatal spleen to secrete sufficient quantities of IL-1.