CD4 and bronchopulmonary dysplasia: Similarly, when CD4+ T cells and PMN-MDSCs were co-cultured in the ratio of 2 : 1, 4 : 1, and 8 : 1, the CD4+ T cells proliferation in BPD group was significantly higher than that in non-BPD preterm infants group (P < 0.05, P < 0.01).