PTGDR2 and infection: They are defined by biomarkers, including CD127 (IL-7Rα), CD161 (Klrg1) and CD294 (CRTH2) (75) (Table 2), which originate from the common lymphoid progenitor (CLP) in the fetal liver or bone marrow and migrate to peripheral tissues to develop into tissue-resident lymphocytes to combat specific types of infections (88, 89).