Presence of B220 within thymocytes and its expression on the cell surface during apoptosis

Abstract

SUMMARYB220 is the full-length splicing isoform of a tyrosine phosphatase CD45 and is predominantly expressed as a transmembrane protein on B cells. Other splicing isoforms of CD45 are yielded by alternative splicing of exons 4, 5 and 6. Recently, the expression of B220 on peripheral T cells during activation-induced cell death has been reported. To investigate whether B220 is implicated in apoptosis of immature T cells, we analysed (by¯ow cytometry using the anti-B220 monoclonal antibody, RA3-6B2) the expression of B220 on mouse thymocytes undergoing X-irradiation-and dexamethasone (DEX)-induced apoptosis. The expression of B220 on thymocytes positive for Thy-1 was induced by X-irradiation or DEX treatment and increased with length of incubation. The expression of B220 was pronounced on the apoptotic hypodiploid cells in the fraction showing lower forward scattering values. Reverse transcription±polymerase chain reaction detected mRNA containing exons 4, 5 and 6 of CD45 in normal thymocytes as well as those exposed to X-rays or DEX. Surprisingly, cytoplasmic B220 antigens were detected in a considerable fraction of normal thymocytes. Moreover, the expression level of the 220 000-MW protein in normal thymocytes was similar to that in the thymocytes undergoing apoptosis. During apoptosis, the expression level of B220 antigen was reduced in the cytoplasm but, conversely, up-regulated on the surface of thymocytes. These results suggest that B220 is constitutively expressed as a cytoplasmic form within thymocytes and possibly translocated to the cell membrane during apoptosis.

A Unique Population of Extrathymically Derived αβTCR+CD4−CD8− T Cells with Regulatory Functions Dominates the Mouse Female Genital Tract

“…This has been reported in thymocytes following irradiation (33), as well as in peripheral T cells and CD8 ϩ T cells following activation (34). In the lpr/gld mouse (35), Mixter et al (36) found a large proportion of the CD3 ϩ cells that were also B220 ϩ , which accumulated in these animals and were not undergoing apoptosis.…”

“…In the lpr/gld mouse (35), Mixter et al (36) found a large proportion of the CD3 ϩ cells that were also B220 ϩ , which accumulated in these animals and were not undergoing apoptosis. Thus, an emerging theory argues that expression of B220 on T cells may be a preconditioning stage for Fas-mediated apoptosis (33). However, using TUNEL staining on frozen sections of the uterus, we could not detect increased levels of apoptotic CD3 ϩ cells in the genital tract compared with spleen or gut intestine (M. Johansson, unpublished observation).…”

Gaucher disease geneGBAfunctions in immune regulation

“…Increased activated B cells are seen in the thymus of patients with myasthenia gravis (26). However, B220 expression is also increased on apoptotic immature T cells (27,28). This suggests that thymic B220 + cells may also regulate T-cell apoptosis.…”

The Surface Glycoprotein of Feline Leukemia Virus Isolate FeLV-945 Is a Determinant of Altered Pathogenesis in the Presence or Absence of the Unique Viral Long Terminal Repeat

“…5). Thus, CD45R expression in these cases may not reflect B-cell origin as it is typically interpreted but appears to reflect tumor origin in normal thymocytes or certain abnormal and activated T cells in which CD45R is also expressed (28)(29)(30)(31)(32)(33)(34)(35). The tumors were evident in bone marrow and blood at earlier times during the disease process, an observation that may reflect either the tissue of origin or the pattern of metastasis.…”

“…4). While CD45R is typically considered a marker of B-cell origin, it is also expressed in the cytoplasm of normal thymocytes and on the surface of a subset of dendritic cells and certain abnormal and activated T cells (28)(29)(30)(31)(32)(33)(34)(35). Thus, CD45R expression in this case may reflect a T-cell origin of the tumors.…”