CD4 and Allergy: We then compared the stimulatory capacity of apo- versus holo- Bos d 5 on human primary immune cells in vitro; unexpectedly, stimulation with holo-Bos d 5 led to a significant decrease in the CD3+ CD4+ cell subset, compared to cells exposed to apo-Bos d 5, indicating an immunosuppressive effect on this population which is pivotal in allergy induction44.