In the mouse model the involvement of NK cells is debated; whereas works from the team of MacDonald [19,62] support an involvement of NK1.1+ NK cells in the protective response, we recently failed [18] to demonstrate a potent role for NCR1+ NK cells in the immune response of neonatal mice to the infection with C. parvum. The use of different markers to analyse NK cells makes it difficult to compare results from different studies but, more importantly, the distribution of the different lymphoid cell types within the gut mucosa of neonates differs notably between ruminants and mice. Here, NCR1 is linked to infection.