Circulating specific antibodies enhance systemic cross-priming by delivery of complexed antigen to dendritic cells in vivo

Increasing evidence suggests that antibodies can have stimulatory effects on T-cell immunity. However, the contribution of circulating antigen-specific antibodies on MHC class I cross-priming in vivo has not been conclusively established. Here, we defined the role of circulating antibodies in cross-presentation of antigen to CD8 + T cells. Mice with hapten-specific circulating antibodies, but naϊve for the T-cell antigen, were infused with haptenated antigen and CD8 + T-cell induction was measured. Mice with circulating hapten-specific antibodies showed significantly enhanced cross-presentation of the injected antigen compared with mice that lacked these antibodies. The enhanced cross-presentation in mice with circulating antigen-specific antibodies was associated with improved antigen capture by APCs. Importantly, CD11c + APCs were responsible for the enhanced and sustained cross-presentation, although CD11c - APCs had initially captured a significant amount of the injected antigen. Thus, in vivo formation of antigen-antibody immune complexes improves MHC class I cross-presentation, and CD8 + T-cell activation, demonstrating that humoral immunity can aid the initiation of systemic cellular immunity. These findings have important implications for the understanding of the action of therapeutic antibodies against tumor-associated antigens intensively used in the clinic nowadays.

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