ENGRAFTED HUMAN T-LYMPHOCYTES AND B-LYMPHOCYTES FORM MIXED FOLLICLES IN LYMPHOID ORGANS OF HUMAN MOUSE AND HUMAN/RAT RADIATION CHIMERA/

Background. We recently described a new approach that enables the gene ration of human/mouse chimera by adoptive transfer of human peripheral blood mononuclear cells into lethally irradiated normal strains of mi ce or rats, radioprotected with bone marrow from donors with severe co mbined immune deficiency. In such human/mouse chimera, a marked humora l response to recall antigens, as well as a significant primary respon se to keyhole limpet hemocyanin, has been generated. Methods. In the p resent study, the organ distribution of the engrafted human cells in t he human/mouse and human/rat chimera was investigated by immunohistoch emistry. Results. Our results show that the T cells seem to be distrib uted throughout the reticular endothelial system, almost behaving like particles without any homing specificity. The B cells, however, can b arely be found in internal organs, such as the liver or the pancreas, and are concentrated in the secondary lymphoid system (e.g., spleen, l ymph node, and nonencapsulated lymphoid tissue). The B cells, together with the engrafted human T cells, form mixed lymphoid follicles. Conc lusions. The different homing patterns exhibited by the T and B lympho cytes indicate that the homing receptors on human B cells might be cro ssreactive with their mouse counterparts, in contrast to the human T c ells, which seem to be unable to interact with the mouse homing recept ors. The presence of human B and T lymphocytes in close proximity to e ach other in the lymphoid tissues is in accordance with the ability of human/BALB radiation chimera to mount significant primary human antib ody responses.