Surface immunoglobulins mediate efficient transport of antigen to lysosomal compartments resulting in enhanced specific antigen presentation by B cells.
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.
Liu
K J
KJ
Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, IL 60611.
Parikh
V S
VS
Tucker
P W
PW
Kim
B S
BS
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D017951:Antigen Presentation; D001402:B-Lymphocytes / Q000502:physiology*; D001692:Biological Transport; D007075:Immunoglobulin M / Q000502:physiology*; D008247:Lysosomes / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009113:Muramidase / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D014162:Transfection
D000911:Antibodies, Monoclonal; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D011505:Protein-Tyrosine Kinases; D009113:Muramidase