Alzheimer disease (AD) is characterized by the progressive deposition of the 42-residue amyloid β protein (Aβ) in brain regions serving memory and cognition. In animal models of AD, immunization with Aβ results in the clearance of Aβ deposits from the brain. However, a trial of vaccination with synthetic human Aβ1–42 in AD resulted in the development of meningoencephalitis in some patients. We measured cellular immune responses to Aβ in middle-aged and elderly healthy subjects and in patients with AD. A significantly higher proportion of healthy elderly subjects and patients with AD had strong Aβ-reactive T cell responses than occurred in middle-aged adults. The immunodominant Aβ epitopes in humans resided in amino acids 16–33. Epitope mapping enabled the identification of MHC/T cell receptor (TCR) contact residues. The occurrence of intrinsic T cell reactivity to the self-antigen Aβ in humans has implications for the design of Aβ vaccines, may itself be linked to AD susceptibility and course, and appears to be associated with the aging process.

Multiple sclerosis (MS) is postulated to be a T cell-mediated autoimmune disease characterized clinically by a relapsing-remitting (RR) stage followed by a secondary progressive (SP) phase. The progressive phase is felt to be secondary to neuronal degenerative changes triggered by inflammation. The status of the innate immune system and its relationship to the stages of MS is not well understood. Dendritic cells (DCs) are professional APCs that are central cells of the innate immune system and have the unique capacity to induce primary immune responses. We investigated circulating myeloid DCs isolated directly from the blood to determine whether there were abnormalities in myeloid DCs in MS and whether they were related to disease stage. We found that SP-MS subjects had an increased percentage of DCs expressing CD80, a decreased percentage expressing PD-L1, and an increased percentage producing IL-12 and TNF-α compared with RR-MS or controls. A higher percentage of DCs from both RR and SP-MS patients expressed CD40 compared with controls. We then investigated the polarization effect of DCs from MS patients on naive T cells taken from cord blood using a MLR assay. Whereas DCs from RR-MS induced higher levels of Th1 (IFN-γ, TNF-α) and Th2 (IL-4, IL-13) cytokines compared with controls, DCs from SP-MS only induced a polarized Th1 response. These results demonstrate abnormalities of DCs in MS and may explain the immunologic basis for the different stages and clinical patterns of MS.

MULTIPLE SCLEROSIS (MS) is an acquired and chronic white matter disease of presumed autoimmune pathogenesis. Results of pathologic studies^1-4 of the disease and of the animal model—experimental autoimmune encephalomyelitis—emphasize mainly a T-cell basis for an inflammatory reaction of demyelinating plaques. However, beyond the well-known intrathecal overproduction of immunoglobulins in patients with MS,⁵ there is also clear evidence of humoral immune activity in these plaques.^6,7 Results of previous studies^8-10 of the frequency of antibodies against myelin oligodendrocyte antigens, such as myelin basic protein (MBP) and galactocerebrosidase in serum and cerebrospinal fluid (CSF), show that elevated titers of these antibodies are not specific for MS. This raises the dilemma of whether these antibodies are deleterious or play a defensive role against further autoimmune attack after myelin breakdown.¹¹