Immunological dysfunction and mast cell activation syndrome in long COVID.

At least 65 million people around the world suffer from long COVID-19, with the majority of cases occurring in the productive age (36-50 years old). Individuals with long COVID-19 are confounded with multiple organ system dysfunctions, long-term organ injury sequelae, and a decreased quality of life. There is an overlapping of risk factors between long COVID-19 and other postviral infection syndromes, so advances in research could also benefit other groups of patients. Long COVID-19 is the consequence of multiple immune system dysregulation, such as T-cell depletion, innate immune cell hyperactivity, lack of naive T and B cells, and elevated signature of pro-inflammatory cytokines, together with persistent severe acute respiratory syndrome-coronavirus 2 reservoir and other consequences of acute infection. There is an activated condition of mast cells in long COVID-19, with abnormal granulation and excessive inflammatory cytokine release. A study by Weinstock et al. indicates that patients with long COVID-19 suffer the same clinical syndrome as patients with mast cell activation syndrome (MCAS). Diagnosis and treatment of MCAS in patients with long COVID-19 will provide further symptomatic relief, and manage mast cell-mediated hyperinflammation states, which could be useful in the long-term control and recovery of such patients.