Despite the vast amount of literature on non-specific immune mechanisms in Alzheimer’s disease (AD), little is known about the role of antigen-specific immune responses. We investigated T cell reactivity to fragment 1–42 of amyloid-β (Aβ) and to N-terminal peptides of human mitochondrial and control microbial proteins. Thirty subjects with a diagnosis of probable AD according to NINCDS-ADRDA criteria and 30 sex- and age-matched healthy controls were enrolled. T cell responses to Aβ fragment showed no significant differences between AD patients and controls. By contrast, the mean number of positive T cell responses to both human mitochondrial and microbial peptides was significantly decreased in AD patients compared to control subjects. No significant correlation was found between T cell responses and both the severity of cognitive impairment and duration of the disease. Our results suggest that antigen-specific immune responses are impaired in AD. Protective immune responses to harmful amyloidogenic substances may also be impaired, thus favoring their accumulation in the brain.
Pre-immunization with autoantigens confers resistance in experimental models of autoimmune diseases. Since non-self molecules can also be protective, it is conceivable that part of the effect rests on a non-specific attenuation of the immune response. This study is aimed at identifying mechanisms by which pre-immunization with a moiety suspended in incomplete Freund's adjuvant (IFA) protects from experimental allergic encephalomyelitis (EAE). Lewis rats were immunized with each of either concanavalin A, lipopolysaccharide, bovine serum albumin, 70 or 65 kDa heat shock proteins, or myelin basic protein. All moieties were given in IFA 3 weeks prior to EAE induction. Serial cytofluorimetric monitoring of B cells and of the alpha beta TCR+, CD4+, CD8+, CD45high and CD45low cells was performed. IFN-gamma and IgG1 production was evaluated in parallel. All moieties were able to attenuate or abrogate the clinical signs of EAE. At day 4 and 10 after EAE induction, the surface expression of the CD4 molecule was down-regulated on T lymphocytes. This down-regulation was most evident in animals with the highest degree of clinical protection. By day 21 post-immunization, CD4 expression was restored. The same animals also showed an increase in the B cell percentage and Th2-related IgG1 production while IFN-gamma secretion was reduced. Pre-immunization with diverse antigens suspended in IFA confers resistance to EAE induction. The down-regulation of the CD4 co-receptor accompanied by events suggestive of an immune deviation may be a general mechanism that contributes to the protection.
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