Suppression of mixed lymphocyte reactivity by cellular and humoral factors in aplastic anemia―both before and after bone marrow transplantation

A patient with infectious hepatitis who developed severe aplastic anemia received a bone marrow transplant from her HLA-identical, mixed lymphocyte culture (MLC)-negative sister. It was found that pretreatment of normal lymphocytes with the immunoglobulin fraction of the patient’s serum resulted in marked inhibition of their proliferative response to mitogens, as well as their ability to serve as stimulators and responders in MLC. The patient’s lymphocytes, unlike those of her HLA-identical sister were unable to stimulate and respond in MLC and markedly suppressed mixed lymphocyte reactivity between two unrelated healthy individuals. Donor-type lymphocytes obtained from the patient after engraftment were also unable to respond or stimulate in MLC. It is suggested that the suppression of lymphocyte responses was mediated by an immunoglobulin present in the patient’s serum.