B2M and postural orthostatic tachycardia syndrome: Notably, the most upregulated plasma protein within the proinflammatory pathway in POTS was beta-2-microglobulin (B2M), which is a component of the major histocompatibility complex class I. Ongoing inflammation is associated with elevated levels of β2M25, likewise, increased levels of B2M have been reported in several autoimmune diseases.