A clue pointing specifically toward a role for TLR9 in defense against coronaviruses, arises from a paper published in 2004 describing that in response to SARS-CoV infection, TLR9 on human PBMCs from healthy donors was surprisingly high expressed in comparison to other TLR receptors (p-value of 0.016) (Ng et al., 2004). The gene discussed is TLR9; the disease is severe acute respiratory syndrome.