Basophils enhance immunological memory responses

Denzel, A., et al. Nat. Immunol. 9, 733-742 (2008)

Speaker: Shih-Ping Chang (張時斌)                               Time: 15:00~16:00, Oct. 15, 2008

Commentator: Dr. Mei-Chi Hsu (許媺祺博士)              Place: Room 601

Abstract:

Immunological memory of humoral response is maintained by circulating antibodies produced by long-lived plasma cells and memory B cell populations that kept long-term survival and proliferate to secrete antibodies after encountering specific antigens, which presented by antigen-capturing cells. B220^-CD19^- cells, a non-B cell population, have been shown to be the antigen-capturing cells in the bone marrow, spleen and peripheral blood (1). Recent studies have characterized such antigen-capturing cells as basophils, a subset of granulocytes that have been linked mainly to allergic reactions and host defense against parasite infections (2), yet, the involvement of basophils in humoral memory immune responses remains unclear. There are not many basophil studies due to the lack of basophil-deficient mouse models and limitations in the number of human basophils available. In this study, the authors have developed a protocol to deplete basophils in mice in vivo. The results showed that basophils expressing FcεRI bound intact antigens through antigen-specific IgE on the cell surface and produced IL-6 and IL-4 in the spleen and the bone marrow after activation. Once basophils were depleted, lower humoral memory response was observed, and such response could also be found after vaccination. Adoptive transfer studies confirmed that antigen-reactive basophils markedly enhanced the memory response by increasing antigen-specific antibody production and B cell proliferation. In vitro experiments further investigating the interaction between basophils, B cells, and CD4⁺ T cells showed that basophil-dependent enhancement of humoral memory response relied on activated basophlis to support T_H2 cell activation that further helped B cell effector function and to secrete IL-6 for B cell stimulation. Collectively, basophils greatly contribute to humoral memory response by promoting T_H2-cell dependent B-cell help.

References:

1.         Bell, J., and D. Gray. 2003. Antigen-capturing cells can masquerade as memory B cells. J Exp Med 197:1233-44.

2.         Mack, M., M. A. Schneider, C. Moll, J. Cihak, H. Bruhl, J. W. Ellwart, M. P. Hogarth, M. Stangassinger, and D. Schlondorff. 2005. Identification of antigen-capturing cells as basophils. J Immunol 174:735-41.