Presentation of a viral peptide assembled on the carbohydrate moieties of immunoglobulin does not require processing

We have previously demonstrated that an immunodominant CD4 T cell epitope, HA110-120 of the hemagglutinin (HA) of the A/PR/8/34 influenza virus, enzymatically assembled on the carbohydrate moieties of self immunoglobulins (Ig) primed the precursors of peptide-specific T cells and induced efficient proliferation in vivo of naive lymphocytes from transgenic mice expressing the peptide-specific T cell receptor. Here, we show that an immuno-galacto-peptide construct, IgG-gal-HA, does not require intracellular or extracellular processing to present the peptide to the specific T cells. The presentation occurs following the binding of the IgG-gal-HA construct to Fc gamma receptor on the surface of antigen-presenting cells (APC), with concurrent interaction of the peptides to their neighboring major histocompatibility complex class II molecules. This mechanism of peptide presentation may harness the immune response in vivo by the engagement of APC with a low capacity of antigen processing, such as neonatal B cells. In addition, the enzymatic method of assembling various aminated compounds on the sugar moieties of Ig may offer novel perspectives on immuno-targeting of antagonist peptides, cytostatic drugs, and biologically active ligands of therapeutic use.