CR2 and hydrops fetalis: Using PKH staining on cells of infested BB and HF re-stimulated with 5 μg/mL antigen or DPBS, a significant antigen specific proliferation in all investigated cell populations (αβ T-cells, γδ T-cells, B-cells, NK-cells and CD3−/CD21−/CD335− cells) was observed, with the highest reaction seen in NK- and CD3−/CD21−/CD335− cells (Figures 2C and D).