Fig. 2

Overview of lymphocytes in the circulating blood and their alterations in neurodegenerative diseases. Peripheral blood mononuclear cells (PBMC) can be isolated from whole blood derived from the blood vessels. PBMC can be further separated into T and B lymphocytes depending on the surface expression of either cluster of differentiation (CD)3 or CD19, respectively. T lymphocyes are further subdivided into T helper cells (CD4+) or cytotoxic T cells (CD8+). Expression of CD4 and CD45RA labels naive Th cells, while expression of CD4 and CD45RO is indicative for memory Th cells. Once activated, Th cells express CD25. Activated Th lymphocytes can be further characterised by the production of cytokines (IL-17, IFNg, IL-4, IL-9, IL-10/TGFb). Disease-specific alterations of the respective lymphocyte subtypes are indicated by arrows (green arrows for PD, orange arrows for AD, and purple arrows for MS). PBMC = peripheral blood mononuclear cells; CD = cluster of differentiation; Th = T helper cells; IL = Interleukin; IFNg = Interferon gamma; TGFb = Transforming growth factor beta; Treg = regulatory T cells; AD = Alzheimer’s disease; PD = Parkinson’s disease; MS = Multiple Sclerosis