We searched PubMed and Google Scholar for articles published in English from Jan 1, 2020, to July 31, 2020, using the search terms “COVID-19”, “coronavirus“, “IL-33”, “ST2”, “type-2 innate lymphoid cells (ILC-2)”, “gamma delta T cells”, “T cells”, “macrophages”, “mast cells”, “neutrophils”, “endothelial cells”, “adipocytes”, “IL-17”, “IL-7 “, “IL-9”, “GM-CSF”, “cytokines”, “chemokines”, “bronchoalveolar lavage fluid (BALF)”, “lung”, “heart”, “hyperinflammation”, “vasculitis”, “thrombosis”, “adult respiratory distress syndrome (ARDS)”, “hemophagocytic lymphohistiocytosis (HLH)”, “macrophage activation syndrome (MAS)”, “obesity”, and “treatment”.