Expression of p75 chain of IL-2 receptor in the early immunological reconstitution after allogeneic bone marrow transplantation.

Expression of p55 and p75 chains of IL-2 receptor (IL-2R) on the surface of both T and natural killer (NK) circulating lymphocytes was investigated in 14 paediatric patients given allogeneic bone marrow transplantation (BMT) from HLA-identical sibling or partially matched family donors. IL-2-induced proliferative and cytotoxic responses were also studied and all analysis was performed within 45 days from transplant. We found that, early after transplant, the percentage of p55+ and of p75+ peripheral blood lymphocytes (PBL) was not significantly different in patients who had received HLA-identical BMT (p55+ 8.04 +/- 4.87%; p75+ 28.27 +/- 18.85%) compared with healthy controls (p55+ 7.26 +/- 6.17%; p75+ 19.42 +/- 10.49%), while recipients of T cell-depleted marrow included a remarkably high percentage (76-90%) of p75+ PBL, which were mostly CD3- and co-expressed CD56 molecule. Comparable values of p55+ lymphocytes were observed in all patients and controls. However, in contrast to the other two groups, in recipients of T cell-depleted BMT the majority of these cells co-expressed p75 chain and CD56 antigen. IL-2-induced proliferation and lymphokine-activated killer (LAK) activity were detectable in all patients, and their values did not correlate with expression of p55 or p75 chains. Our data suggest that expansion of NK subsets expressing IL-2R chains after T cell-depleted BMT may be related to early reconstitution of natural immunity in the presence of allogeneic stimuli.