Cellular requirements for mixed leucocyte reactivity in the cyclostome, Eptatretus stoutii

Unfractionated peripheral blood leucocytes from allogeneic hagfish proliferated vigorously in one-way mixed leucocyte reaction (MLR) at 20-22 degrees. Maximum responsiveness was observed after 5 days of co-culture of responder and irradiated stimulator cells. Separation of leucocytes on the basis of laser scatter parameters yielded a small leucocyte population which responded but did not stimulate in MLR and a large leucocyte population capable of stimulating but not responding. Adherent cell depletion of the total leucocyte population did not affect the ability to respond in MLR but did ablate the stimulatory capacity of hagfish leucocytes. Together with previous phenotypic studies, these results confirm the presence of lymphocyte and macrophage/accessory cell populations in hagfish peripheral leucocytes.