Immune aging occurs in the elderly and in autoimmune diseases. Recently, IgDCD27 (double negative, DN) and CD21CD11c (CD21) B cells were described as age-associated B cells with proinflammatory characteristics. This study investigated the prevalence and functional characteristics of DN and CD21 B cells in multiple sclerosis (MS) patients. Using flow cytometry, we demonstrated a higher proportion of MS patients younger than 60 y with peripheral expansions of DN (8/41) and CD21 (9/41) B cells compared with age-matched healthy donors (1/33 and 2/33, respectively), which indicates an increase in age-associated B cells in MS patients. The majority of DN B cells had an IgG memory phenotype, whereas CD21 B cells consisted of a mixed population of CD27 naive, CD27 memory, IgG, and IgM cells. DN B cells showed similar (MS patients) or increased (healthy donors) MHC-II expression as class-switched memory B cells and intermediate costimulatory molecule expression between naive and class-switched memory B cells, indicating their potential to induce (proinflammatory) T cell responses. Further, DN B cells produced proinflammatory and cytotoxic cytokines following ex vivo stimulation. Increased frequencies of DN and CD21 B cells were found in the cerebrospinal fluid of MS patients compared with paired peripheral blood. In conclusion, a proportion of MS patients showed increased peripheral expansions of age-associated B cells. DN and CD21 B cell frequencies were further increased in MS cerebrospinal fluid. These cells could contribute to inflammation by induction of T cell responses and the production of proinflammatory cytokines.

Follicular regulatory T cells (TFR) have been extensively characterized in mice and participate in germinal center responses by regulating the maturation of B cells and production of (auto)antibodies. We report that circulating TFR are phenotypically distinct from tonsil-derived TFR in humans. They have a lower expression of follicular markers, and display a memory phenotype and lack of high expression of B cell lymphoma 6 and ICOS. However, the suppressive function, expression of regulatory markers, and FOXP3 methylation status of blood TFR is comparable with tonsil-derived TFR. Moreover, we show that circulating TFR frequencies increase after influenza vaccination and correlate with anti-flu Ab responses, indicating a fully functional population. Multiple sclerosis (MS) was used as a model for autoimmune disease to investigate alterations in circulating TFR. MS patients had a significantly lower frequency of circulating TFR compared with healthy control subjects. Furthermore, the circulating TFR compartment of MS patients displayed an increased proportion of Th17-like TFR. Finally, TFR of MS patients had a strongly reduced suppressive function compared with healthy control subjects. We conclude that circulating TFR are a circulating memory population derived from lymphoid resident TFR, making them a valid alternative to investigate alterations in germinal center responses in the context of autoimmune diseases, and TFR impairment is prominent in MS.

Microglial activation is a hallmark of all neurodegenerative diseases including amyotrophic lateral sclerosis (ALS; SOD1 G93A doubly transgenic mice had no effect on motor neuron degeneration. This suggests that proliferating microglia-expressing mutant SOD1 are not central contributors of the neurodegenerative process in ALS caused by mutant SOD1.