PAX5 and lymphopenia: Lymphopenia characterized by a drastic reduction of lymphocytes is generally accompanied by a poor prognosis of COVID-19 patients.278 PGE2 can suppress PAX5, a regulator of B cell proliferation and survival, thereby partially contributing to the lymphopenia.279 A comparatively low level of PGE2 enhances immunity while a high level of it compromises the immune system by killing lymphocytes.280 Another prostaglandin PGD2, synthesized by COX, also contributes to lymphopenia.