Susumu Ikehara

Presence of B cell progenitors in the thymus.

We characterize B cell progenitors in the thymus. Although mature thymic B cells are surface Ig+, B220(high), but CD43-, B cell progenitors in the thymus were found to be slg-, B220(med), and CD43+. Most progenitors showed rearranged Ig D-J and V-D-J patterns when DNA from sorted B cell progenitors was amplified by PCR, blotted, and probed. When B cell progenitors were purified from the thymus and injected intrathymically into Ig heavy chain (Igh) allotype-disparate recipients, B cells bearing donor-type Igh6 were detected in the thymus but not in the periphery. Thymic B cells generated from these progenitors were CD5+ cells, although there was a broad range of expression of CD5 molecules. Furthermore, B cells purified from thymus that had been inoculated with B cell progenitors were able to differentiate into Ab-forming cells under the influence of CD40 ligand plus IL-10, and secreted IgM with donor Igh6 allotype. We thus clarified the existence of B cell progenitors in the thymus and also characterized the surface markers and their developmental functions.

Expression of CD45-Restricted Form B in (NZW × BXSB) F1 and MRL/Mp-1pr/1pr Mice

Expression of CD45RB on CD4+ or CD8+ cells in combination with TCRV beta usages (V beta 6, V beta 8.1, V beta 8.2, V beta 11 and V beta 17a) in normal mouse strains (BALD/c and C57BL/6) was compared with autoimmune-prone strains (NZW x BXSB) F1 and MRL/lpr) at young and old ages. The frequencies, and also the numbers of CD45RB- cells in CD4+ T cells with various TcR repertoires was significantly less in the autoimmune-prone stains at old ages, while, in normal control strains, they remained unchanged. Furthermore, CD4+/CD45RB- cells are CD44high and CD62L (L- selectin).low These findings suggest that most T cells, especially CD4+ T cells, in old W/BF1 and old MRL/lpr mice, were activated and this may reflect the elevation of autoantibodies and the progress of autoimmune status in aged autoimmune-prone mice. This will be discussed in relation to the progress of the autoimmune diseases.

Two natural killer-cell subpopulations distinguished by heat sensitivity

We examined the effect of heat on natural killer-cell activity and found that two different natural killer-cell subpopulations can be distinguished by their heat sensitivity; one subpopulation loses natural killer-cell activity at 41°C, and the other is not affected. In a single-cell assay, the ability of natural killer cells to conjugate to K 562 cells was not affected by incubation at 41°C, but the killer activity of natural killer cells after conjugating to K 562 cells was reduced at 41°C. Therefore it is likely that the difference in heat sensitivity between the two subpopulations is due to postbinding cytolytic events. Tetracaine, which influences cytolytic events, was used to examine whether or not the two natural killer-cell subpopulations can be distinguished by tetracaine sensitivity. However, it was found that tetracaine inhibits natural killer-cell activity equally for both of these natural killer-cell subpopulations.

Intra-Bone Marrow-Hematopoietic Stem Cell Transplantation; A Powerful Tool for Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) was originally developed to treat hematopoietic diseases, congenital immunodeficiency, leukemia, and so on. Subsequently, the technique has been used to treat solid tumors, autoimmune diseases and metabolic disorders. Although improvements have been made to the protocol, the associated risks are still high. To minimize these risks, we have established a new HSCT protocol, intra-bone marrow-hematopoietic stem cell transplantation (IBM-HSCT). IBMHSCT reduces graft versus host disease (GVHD), and accelerates hematopoiesis of donor bone marrow cells, resulting in the rapid recovery of hematopoiesis after the BMT.

Fate of Engrafted Skin in Thymic Chimeras

There have been some investigations concerning the mechanisms of self-toler anceusing thymic chimeras with organ transplantation. In heart transplantation to nude mice bearing allogeneic thymus, Seger et al (15) found that neonatal heart grafts of thymus donor origin were rejected, but another group (17) showed that they were accepted. There are also conflicting reports regarding the fate of engrafted skin on thymus chimeras. Kindred and Loor (12) studied the mode of skin grafts in BALB/c nu/nu mice engrafted with C57BL/6 thymus and found that some mice accepted but some mice rejected the skin of the thymus donor. However, Pritchard and Micklem (14) observed that thymic chimeras accepted the skin of the thymus donor and rejected the skin of a third party. Recently, some groups (3, 6, 8) demonstrated that thymic chimeras accepted the skin of both thymus-type and host-type. In spite of this accumulated evidence, the effects of donor and host conditions on the fate of en graftedskins described below have not been considered precisely. The final goal of these studies is to establish an immunological requirement for treatment of pa tientswith immunodeficiency by thymus grafting. Therefore, it is very important to elucidate whether the conditions in host and donor, even if they are not major problems, affect the fate of engrafted skin. In this study our attention was focused on the following factors: 1) the presence of postthymic T cells in nude mice and the possibility of these T cells expanding under the influence of the engrafted thymus (7), 2) the effect of immunocompetent T cells in the engrafted thymus, 3) the size of engrafted skin (16), and 4) the duration of engrafted skin survival because skin antigen presenting cells take 65-80 days to be replaced by bone marrow precursors