Leptin-based hexamers facilitate memory and prevent amyloid-driven AMPA receptor internalisation and neuronal degeneration.

Key pathological features of Alzheimer's disease (AD) include build-up of amyloid ß (Aß), which promotes synaptic abnormalities and ultimately leads to neuronal cell death. Metabolic dysfunction is known to influence the risk of developing AD. Impairments in the leptin system have been detected in AD patients, which has fuelled interest in targeting this system to treat AD. Increasing evidence supports pro-cognitive and neuroprotective actions of leptin and these beneficial effects of leptin are mirrored by a bioactive leptin fragment (leptin116-130 ). Here we extend these studies to examine the potential cognitive enhancing and neuroprotective actions of 8 six-amino acid peptides (hexamers) derived from leptin116-130 . In this study, we show that four of the hexamers (leptin116-121, 117-122, 118-123 and 120-125 ) replicate the ability of leptin to promote α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor trafficking and facilitate hippocampal synaptic plasticity. Moreover, the pro-cognitive effects of the hexamers were verified in behavioural studies, with the administration of leptin117-122 enhancing performance in episodic memory tasks. The bioactive hexamers replicated the neuroprotective actions of leptin by preventing the acute hippocampal synapto-toxic effects of Aß, and the chronic effects of Aß on neuronal cell viability, Aß seeding and tau phosphorylation. These findings provide further evidence to support leptin and leptin-derived peptides as potential therapeutics for AD.

Effective Priming of Herpes Simplex Virus-Specific CD8+ T Cells In Vivo Does Not Require Infected Dendritic Cells.

Resolution of virus infections depends on the priming of virus-specific CD8+ T cells by dendritic cells (DC). While this process requires major histocompatibility complex (MHC) class I-restricted antigen presentation by DC, the relative contribution to CD8+ T cell priming by infected DC is less clear. We have addressed this question in the context of a peripheral infection with herpes simplex virus 1 (HSV). Assessing the endogenous, polyclonal HSV-specific CD8+ T cell response, we found that effective in vivo T cell priming depended on the presence of DC subsets specialized in cross-presentation, while Langerhans cells and plasmacytoid DC were dispensable. Utilizing a novel mouse model that allows for the in vivo elimination of infected DC, we also demonstrated in vivo that this requirement for cross-presenting DC was not related to their infection but instead reflected their capacity to cross-present HSV-derived antigen. Taking the results together, this study shows that infected DC are not required for effective CD8+ T cell priming during a peripheral virus infection.IMPORTANCE The ability of some DC to present viral antigen to CD8+ T cells without being infected is thought to enable the host to induce killer T cells even when viruses evade or kill infected DC. However, direct experimental in vivo proof for this notion has remained elusive. The work described in this study characterizes the role that different DC play in the induction of virus-specific killer T cell responses and, critically, introduces a novel mouse model that allows for the selective elimination of infected DC in vivo Our finding that HSV-specific CD8+ T cells can be fully primed in the absence of DC infection shows that cross-presentation by DC is indeed sufficient for effective CD8+ T cell priming during a peripheral virus infection.

Sensitivity and specificity of tritiated thymidine incorporation and ELISPOT assays in identifying antigen specific T cell immune responses.

BACKGROUND: Standardization of cell-based immunologic monitoring is becoming increasingly important as methods for measuring cellular immunity become more complex. We assessed the ability of two commonly used cell-based assays, tritiated thymidine incorporation (proliferation) and IFN-gamma ELISPOT, to predict T cell responses to HER-2/neu, tetanus toxoid (tt), and cytomegalovirus (CMV) antigens. These antigens were determined to be low (HER-2/neu), moderate (tt), and robustly (CMV) immunogenic proteins. Samples from 27 Stage II, III, and IV HER-2/neu positive breast cancer patients, vaccinated against the HER-2/neu protein and tt, were analyzed by tritiated thymidine incorporation and IFN-gamma ELISPOT for T cell response. RESULTS: Linear regression analysis indicates that both stimulation index (SI) (p = 0.011) and IFN-gamma secreting precursor frequency (p < 0.001) are significant indicators of antigen specific immunity. ROC curves plotted to assess the performance of tritiated thymidine incorporation and the ELISPOT assay indicate that SI is a significant indicator of low T cell response to the HER-2/neu vaccine (p = 0.05), and of moderate and robust responses to tt (p = 0.01) and CMV (p = 0.016), respectively. IFN-gamma precursor frequency is a significant indicator of a robust T cell response to CMV (p = 0.03), but not of moderate tt (p = 0.09), or low HER-2/neu (p = 0.09) T cell responses. CONCLUSION: These data underscore the importance of taking into consideration the performance characteristics of assays used to measure T cell immunity. This consideration is particularly necessary when determining which method to utilize for assessing responses to immunotherapeutic manipulations in cancer patients.