Alloantigen presentation by B cells: analysis of the requirement for B-cell activation.
This paper describes a model for investigation of the functional implications of B-cell activation for antigen presentation. Mixed lymphocyte cultures were used to assess the ability of freshly isolated B cells, mitogen-activated B cells and Epstein-Barr virus (EBV)-transformed B-cell lines to stimulate the activation and proliferation of allogeneic T cells under a variety of experimental conditions. It was found that resting B cells presented antigen poorly, while activated cells were highly immunogenic. Paraformaldehyde fixation completely eliminated antigen presentation by resting B cells, despite constitutive expression of class II MHC antigens. However, fixation had little effect on antigen presentation by activated B cells that expressed B7-1 and B7-2 in addition to class II major histocompatibility complex (MHC) molecules. Arrest of B-cell activation by serial fixation after treatment with F(ab')2 fragments of goat anti-human IgM produced cells with variable antigen-presenting capacity. Optimal antigen presentation was observed for cells fixed 72 hr after the initiation of B-cell activation. Although both B7-1 and B7-2 antigen expression increased after B-cell activation, it was found that the rate of T-cell proliferation correlated most closely with B7-2 expression. Stimulation of T cells by fixed activated B lymphocytes could be blocked by antibodies directed at class II MHC molecules, indicating involvement of the T-cell antigen receptor. In addition, T-cell proliferation was inhibited by antibodies specific for B7-1 and B7-2 and by the fusion protein CTLA4-Ig, demonstrating a requirement for CD28 signal transduction. The sole requirement of B7 family expression for antigen presentation by B lymphocytes was shown by demonstration of T-cell stimulation by fixed resting B cells in the presence of CD28 antibody as a source of artificial costimulation.
Wilson
J L
JL
Department of Surgery, Medical School, University of Newcastle upon Tyne, UK.
Cunningham
A C
AC
Kirby
J A
JA
D017951:Antigen Presentation / Q000502:physiology*; D001402:B-Lymphocytes / Q000276:immunology*; D018122:B7-1 Antigen / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002478:Cells, Cultured; D005434:Flow Cytometry; D004854:Herpesvirus 4, Human; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D006801:Humans; D007519:Isoantigens / Q000276:immunology*; D008213:Lymphocyte Activation / Q000502:physiology*; D008934:Mitogens; D018448:Models, Immunological; D011948:Receptors, Antigen, T-Cell / Q000502:physiology
D018122:B7-1 Antigen; D000949:Histocompatibility Antigens Class II; D007519:Isoantigens; D008934:Mitogens; D011948:Receptors, Antigen, T-Cell