Breastfeeding largely does two things: i) it transmits antibodies from mom to child, the maternal antibodies circulate for a while and so the mom's immune prote

Breastfeeding largely does two things: i) it transmits antibodies from mom to child, the maternal antibodies circulate for a while and so the mom's immune protection is temporarily conferred; ii) it contains potential antigens like peanuts, cow milk, basically anything the mom eats and so it tolerizes the infant's own immune system from common food antigens. There are leukocytes, neutrophils etc. in breast milk, but it is unlikely that they get through the gut lining into the infant.