ENTPD1 and susceptibility to pneumonia measurement: Our study was designed to observe the distribution and absolute numbers (Ab No.)of total Treg (CD4+CD25+FoxP3+), six subsets of Tregs (Helios+/-, CD39+/-, and CD45RA+/-), and T cells, B cells, and NK cells (TBNK) between patients with mild and severe pneumonia after KTx.