The aging of the immune system causes a great deal of damage, and in many different ways. There are many varieties of immune cell in the innate and adaptive portions of the immune system, and pathological subsets are known to arise with age. Take age-associated B cells, for example, or the misconfigured T cells that contribute to varieties of autoimmune disorder, or the regulatory T cells that contribute to the pathology of heart failure, or the macrophages that become foam cells to accelerate atherosclerosis. There are many more examples.
To a first approximation, the immune system of the central nervous system is distinct from that of the rest of the body. The blood-brain barrier separates the two sides, allowing only some traffic to pass between. When looking closer, this is not entirely true, however. T-cells of the adaptive immune system can cross into the cerebrospinal fluid in small numbers, particularly in disease states, and there is evidently some mode of communication between the immune systems of the central nervous system and the rest of the body, given that they both
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