The rejection of primary allografts is classically thought to depend on a form of cellular immunity which resembles delayed hypersensitivity. The site and mechanism of sensitization of effector cells varies with the type of graft. Recent studies suggest that humoral antibodies also play a role in rejection of certain primary allografts such as in patients who have had transfusions or multiple pregnancies.
Rowlands DT, Bossen EH. ImmunologicalMechanisms of Allograft Rejection. Arch Intern Med. 1969;123(5):491-500. doi:10.1001/archinte.1969.00300150009003