Characteristics of intrathymic B cells in normal and chimera mice.

A subpopulation of B cells express Ly-1 (CD5 in human) antigen that is usually expressed on cells of T-cell lineage. This Ly-1+ B cell subpopulation (B1) has a quite different characteristic from the major Ly-1- B cell population (B2), and their physiological role and the functions under pathological conditions have not been thoroughly studied. In the present investigation, characteristic of intrathymic B cells from a variety of mouse strains and allogeneic bone marrow chimeras was studied. B cells were found in the thymic medulla as diffusely scattered pattern among the majority of mouse strains studied. By contrast, in SJL/J and AKR/J mice, intrathymic B cells were arranged in clusters within the medulla, and the proportion of Ly-1+ B cells in the B cell population was significantly lower than that seen in other strains of mice. Further, when B cells in thymi from allogeneic bone marrow chimeras were analyzed, the intathymic B cells were fully reconstituted with donor bone marrow-derived cells but showed the same distribution pattern and phenotype as those of the recipients. These findings indicate that differences in the distribution pattern of a certain B cell subpopulation seen among various mouse strains are determined by the radio-resistant recipient environment (thymic stroma).