CD4 and hydrops fetalis: We previously found that both activated CD4+ T cells (CD44+CD62L−CD4+ T cells), CD8+ T cells (CD44+CD62L−CD8+ T cells), and CD11c+ APCs (particularly the MHCII+CD11c+ APCs) were increased in LV tissues in HF mice [3,16], and inhibition of the crosstalk between T cells and APCs by CD28 knockout, CD86/CD80 double knockout, or depletion of CD11c+ APCs significantly attenuated TAC-induced LV infiltration of the activated CD4+ T cells, CD8+ T cells, MHCII+CD11c+ APCs, and LV inflammation and HF development [3,16].