CXCL13 and COVID-19: Recent studies revealed that CXCL13 serum levels were elevated significantly in patients with severe COVID-19 who were admitted to the intensive care unit (ICU) compared to those with moderate disease, suggesting that measuring CXCL13 in the sera of patients with COVID-19 can be used as a predictive immunological marker for the severity of COVID-19 [58,59].