Abstract
A characteristic feature of COVID-19 disease is lymphopenia. Lymphopenia occurs early in the clinical course and is a predictor of disease severity and outcomes. The mechanism of lymphopenia in COVID-19 is uncertain. It has been variously attributed to the release of inflammatory cytokines including IL-6 and TNF-α; direct infection of the lymphocytes by the virus; and rapid sequestration of lymphocytes in the tissues. Additionally, we postulate that prostaglandin D(2) (PGD(2)) is a key meditator of lymphopenia in COVID-19. First, SARS-CoV infection is known to stimulate the production of PGD(2) in the airways, which inhibits the host dendritic cell response via the DP(1) receptor signaling. Second, PGD(2) is known to upregulate monocytic myeloid-derived suppressor cells (MDSC) via the DP(2) receptor signaling in group 2 innate lymphoid cells (ILC2). We propose targeting PGD(2)/DP(2) signaling using a receptor antagonist such as ramatroban as an immunotherapy for immune dysfunction and lymphopenia in COVID-19 disease.