Muramyl dipeptide (MDP), an agonist of the pattern recognition receptor nucleotide-binding oligomerization domain–containing 2 (NOD2), increases the abundance of LY6Clo NCMs in Nr4a1–/– mice (12); and infection from SARS-CoV-2 virus, which has single-stranded RNA (ssRNA), a natural NOD2 agonist, is associated with the development of a unique NCM subtype with C1q expression in humans. The gene discussed is NOD2; the disease is infection.