Alloantigen presentation by B cells: analysis of the requirement for B-cell activation

• Published in: Immunology 1995-11, Vol.86 (3), p.325-330
• Main Authors: Wilson, J L, Cunningham, A C, Kirby, J A
• Format: Article
• Language: English
• Subjects: Antigen Presentation - physiology; B-Lymphocytes - immunology; B7-1 Antigen - immunology; CD4-Positive T-Lymphocytes - immunology; Cells, Cultured; Flow Cytometry; Herpesvirus 4, Human; Histocompatibility Antigens Class II - immunology; Humans; Isoantigens - immunology; Lymphocyte Activation - physiology; Mitogens; Models, Immunological; Receptors, Antigen, T-Cell - physiology
• ISSN: 0019-2805; 1365-2567

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.