Surface immunoglobulins mediate efficient transport of antigen to lysosomal compartments resulting in enhanced specific antigen presentation by B cells

Abstract

A BCL1 immunoglobulin (Ig) transfectant, expressing wild-type surface (s)IgM with the TEPC-15 idiotype (T15-Id) and anti-phosphorylcholine (PC) specificity, was previously shown to present PC-conjugated hen egg-white lysozyme (PC-HEL) to a HEL-specific T cell hybridoma at a lower antigen (Ag) concentration than that required for native HEL. Two variant Ig transfectants, expressing T15-Id sIgM with substitutions either in the entire spacer, transmembrane (TM) domain and cytoplasmic tail (B186 variant) or in the NH2-terminal third of TM domain only (TM2 variant), failed to display this sIgM-mediated, enhanced presentation of PC-HEL at low concentrations. However, prolonged treatment with anti-T15-Id monoclonal antibody (mAb) led to a reduction of surface expression of the T15-Id sIgM in the wild-type and TM2 variant, but not in the B186 variant sIgM transfectants. Treatment with anti-T15-Id mAb also resulted in an increased intracellular accumulation of T15-Id sIgM in the wild-type transfectant, but not in the B186 variant. Subcellular fractionation analysis revealed that the ligands bound to the T15-Id sIgM are not efficiently transported to the dense lysosomal compartments in both B186 and TM2 transfectants, as compared to the wild-type sIgM transfectant. A significant increase in tyrosine phosphorylation after cross-linking of the T15-Id sIgM was observed only in the wild-type sIgM transfectant. These results suggest that, while the NH2-terminal third of the TM region is not involved in the process responsible for the ligand-induced reduction of surface expression of sIgM, it appears to be essential for subsequent transport of sIgM/ligand complexes to the lysosomal compartments, as well as efficient activation of tyrosine kinases. These results strongly suggest that sIg-mediated enhancement of specific antigen presentation reflects the ability of sIg to efficiently transport antigen to the lysosomal compartments, and possibly the activation of protein tyrosine kinases.

Activation of B cells using Schneider 2 cells expressing CD40 ligand for the enhancement of antigen presentation in vitro

“…For effective induction of T cell mediated immune response, efficient presentation of antigen peptides is required. Among the various APCs including dendritic cells (DC) (Metlay et al, 1989;Romani et al, 1989;Steinman et al, 1993;Salusto et al, 1994;Celluzzi et al, 1996;Paglia et al, 1996), activated macrophages (Rock et al, 1993) or activated B cells (Gollob et al, 1993;Liu et al, 1994;Topalian et al, 1994;Constant et al, 1995;Mitchell et al, 1995;Schultze et al, 1995;Ke et al, 1996;Vidard et al, 1996), lymphoblastoid B cell lines (LCL) (Livingston et al, 1997;Barbara et al, 2002), the best known APC is DC for its potency in antigen capture, processing and migration (Steinman et al, 1993).…”

CD40-activated human B cells: an alternative source of highly efficient antigen presenting cells to generate autologous antigen-specific T cells for adoptive immunotherapy.

“…Induction of productive T cell immunity requires efficient presentation of peptide antigens by professional antigenpresenting cells (APCs). 1 Although dendritic cells (DCs) (5)(6)(7)(8)(9)(10)(11)(12), activated macrophages (13), or activated B cells (14)(15)(16)(17)(18)(19)(20)(21)(22) are all capable of presenting peptides, DCs are considered to be the most efficient APC since fewer DCs are required to induce an optimal T cell immune response (8). In addition to their capacity to present antigen, DCs are also highly efficient at antigen capture, processing, and migration (reviewed in reference 23).…”