The percentage of B220+ IgM+ cells and B220+ IgMC cells in the quadrants are indicated at the top of each quadrant. Removal of B cells in the developing thymus allows the prolonged generation of V6+ T cells A single injection of a given amount of anti-IgM antibodies into neonates just after birth caused the disappearance of B cells in the thymus (Fig. of the absence or immaturity of particular APC with Mls antigens of their own products in the neonatal thymus. In the search for the cellular and histological changes occurring in the newborn thymus, we found that the elimination of V6+ T cells progressed in parallel with the development of thymic B cells. Involvement of B cells in purging the autoreactive T cells from the newborn thymus was shown by prevention of the deletion of V6+ T cells after the removal of B cells by the treatment of neonates with anti-immunoglobulin M antibodies. The restricted and stable expression of CD5 on the thymic B cells, but not on the splenic cells, suggests that these B cells are not postnatal immigrants from the periphery. Finally, it is concluded that the deficiency in the deletion of self-reactive T cells in the thymus of Mls-1a neonates is due to the delayed development of B cells. Introduction Clonal deletion is one of the fail-safe mechanisms involved in the prevention of generating self-reactive T cells, being understood under the advantages Bmp3 of both superantigens, some of which are encoded within endogenous mammary tumour virus (genes in the neonatal thymus was found to be similar to that in the adult one, somewhat contrary to the report of the low-level expression of other genes in the neonatal thymus, 13 and all these genes dealt with were accompanied by a loss of the corresponding V-bearing T cells in the thymus of young adults. In addition to the ontogenic UNC2541 changes of the transcript level in the thymus, both the differences in the amount of 0001) or ?076 ( 0001). Open in a separate window Figure 3 Prominent increase in the number of B cells accompanied by a decrease of V6+ T cells in the thymus of 2-day-old Mls-1a mice receiving spleen cells of adult syngeneic mice. Within 24 hr after birth CAKF1 (Mls-1-positive) mice were i.v. injected with media, as a control, or with 2 107 spleen cells from adult syngeneic mice. Two days after the injection, their thymus cells were analysed by flow cytometry for V6-bearing T cells, DC and B cells. The data were expressed as a mean value against UNC2541 those of the medium-injected controls with a bar SD of the values. number of mice used. Open in a separate window Figure 4 B-cell development in the thymus of neonatal mice. The developmental profile of B cells is inverse to the kinetic profile of autoreactive V6+ T cells in the early thymus of Mls-1a mice as shown in (a) where percentages of IgM+ cells coexpressing B220 in the thymocytes from CAKF1 mice were individually plotted (?) several days after birth, and simultaneously, the developmental kinetics UNC2541 of V6+ T cells () appearing in Fig. 1 is overlapped. Each closed symbol refers to each mouse, or a mean of nine mice with a bar of SD. Thymi from 1- or 6-day-old CAKF1 mice were prepared for immunohistology (b) by staining their sections with FITC-conjugated anti-IgM antibodies: C, thymus cortex; M, medulla; magnification 80; and for flow cytometry (c) in double staining with both anti-B220 and anti-IgM UNC2541 antibodies. The percentage of B220+ IgM+ cells and B220+ IgMC cells in the quadrants are indicated at the top of each quadrant. Removal of B cells in the developing thymus allows the prolonged generation of V6+ T cells A single injection of a given amount of anti-IgM antibodies into neonates just after birth caused the disappearance of B cells in the thymus (Fig. 5a,b) as well as in the periphery, and simultaneously prevented the deletion of V6+ T cells in the CAKF1 thymus.