B7 costimulates proliferation of CD4-8+ T lymphocytes but is not required for the deletion of immature CD4+8+ thymocytes.
In addition to TCR-derived signals, costimulatory signals derived from stimulation of the CD28 molecule by its natural ligand, B7, have been shown to be required for CD4+8- T cell activation. We investigate the ability of B7 to provide costimulatory signals necessary to drive proliferation and differentiation of virgin CD4-8+ T-cells that express a transgenic TCR specific for the male (H-Y) Ag presented by H-2Db class I MHC molecules. Virgin male-specific CD4-8+ T cells can be activated either with B7 transfected chinese hamster ovary (CHO) cells and T3.70, a mAb specific for the transgenic TCR-alpha chain that is associated with male-reactivity, or by male dendritic cells (DC). Activated CD4-8+ T cells proliferated in the absence of exogenously added IL-2. IL-2 activity was detected in supernatants of CD4-8+T3.70+ cells that were stimulated with T3.70 and B7+CHO cells. The response of CD4-8+T3.70+ cells to T3.70/B7+CHO or to male DC stimulation were inhibited by CTLA4Ig, a fusion protein comprising the extracellular portion of CTLA4 and human IgG C gamma 1. It has been previously shown that CTLA4Ig binds B7 with high affinity. Staining with CTLA4Ig revealed that DC express about 50 times more B7 than CD4-8+ T cells. CTLA4Ig also specifically blocked the proliferation of male-reactive cells in vivo. We have also used an in vitro deletion assay whereby immature CD4+8+ thymocytes expressing the transgenic male-specific TCR are deleted by overnight incubation with either immobilized T3.70 or male DC to investigate the participation of the CD28/B7 pathway in the negative selection of immature thymocytes. Staining with B7Ig established that both immature murine CD4+8+ and mature CD4-8+ thymocytes express a high level of CD28. However, despite the high expression of CD28 on CD4+8+ thymocytes, it was found that deletion of CD4+8+ thymocytes expressing the male-specific TCR by the T3.70 mAb was not inhibited by B7+CHO cells. Furthermore, the deletion of these thymocytes by DC also was not inhibited by CTLA4Ig. These findings provide evidence that although signaling through CD28 can costimulate a primary anti-male response in mature CD4-8+ T cells, the CD28/B7 pathway does not appear to participate in the negative selection of immature CD4+8+ thymocytes.
Tan
R
R
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Teh
S J
SJ
Ledbetter
J A
JA
Linsley
P S
PS
Teh
H S
HS
D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology; D000954:Antigens, Surface / Q000032:analysis / Q000502:physiology*; D018122:B7-1 Antigen; D018106:CD28 Antigens; D015704:CD4 Antigens / Q000032:analysis*; D016827:CD8 Antigens / Q000032:analysis*; D016466:CHO Cells; D006224:Cricetinae; D003713:Dendritic Cells / Q000276:immunology; D005260:Female; D007376:Interleukin-2 / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000276:immunology*
D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface; D018122:B7-1 Antigen; D018106:CD28 Antigens; D015704:CD4 Antigens; D016827:CD8 Antigens; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell