Endogenous and exogenous forms of the same antigen are processed from different pools to bind MHC class II molecules in endocytic compartments

Abstract

The current studies were carried out to examine the basis for the differences in the antigenic peptides generated from exogenous and endogenous forms of hen egg white lysozyme (HEL). The role of different intracellular compartments in the generation and binding of HEL peptides derived from two endogenous forms of HEL, either secreted (sHEL) or retained in the endoplasmic reticulum (ER, KDELHEL), presented by MHC class II molecules was examined and compared to exogenous HEL. Initially it was found that antigen-presenting cells bearing both intracellular forms of HEL generated and presented a number of IAk-restricted HEL epitopes to T cell hybridomas, although sHEL was processed more efficiently than KDEL-HEL. There were differences, however, for some determinants between endogenous and exogenous HEL. At equivalent antigen-presenting efficiencies, endogenous HEL-bearing cells displayed a lower surface density of IAk-bound HEL-52-61-related peptides than cells pulsed with exogenous HEL, as detected by a specific monoclonal antibody. Neither endogenous HEL degradation nor peptide binding to MHC class II molecules occurred in the ER. Processing of sHEL and KDELHEL appears to take place either in a post-trans-Golgi network acidic compartment or in the cytosol, whereas peptide binding to MHC class II molecules occurs in endocytic compartments. Furthermore, the peptides generated were derived from an endogenous source rather than from secreted and re-endocytosed HEL. Thus, processing of endogenous HEL is from a different pool than exogenous HEL and occurs in different compartments.

Negligible Class II MHC Presentation of B Cell Receptor-Derived Peptides by High Density Resting B Cells

“…Although our experiments with normal B cells produced a compatible result with respect to a second (V H ) epitope, these assays lacked high sensitivity because so few B cells expressed the corresponding V H gene. Moreover, there is good evidence that different Ags are processed differentially in subcellular compartments associated with MHC presentation (2,61,62). Thus, although there is still no clear precedent, it is conceivable that other BCR-associated epitopes may be presented by truly resting B cells.…”

Brucella abortus Lipopolysaccharide in Murine Peritoneal Macrophages Acts as a Down-Regulator of T Cell Activation

“…OVA was passively adsorbed to latex beads (Polysciences, Warrington, PA) in accordance with the manufacturer's protocol, followed by extensive washing in medium. The HEL-specific CD4 ϩ T cell hybridomas 3A9 and 3B11 are specific for HEL 46 -61 -IK k and HEL 34 -45 -IA k , respectively (19). The OVA-specific CD8 ϩ T cell hybridoma 4B10 is specific for OVA 257-264 -K b (20).…”

Peripheral Tolerance to a Nuclear Autoantigen: Dendritic Cells Expressing a Nuclear Autoantigen Lead to Persistent Anergic State of CD4+ Autoreactive T Cells After Proliferation

“…Regarding the case of Ag-presentation on MHC class II molecules to CD4 ϩ T cells, Ag localization (extracellular vs intracellular) was demonstrated to significantly influence the expression level (6) and processing (4 -6) of Ags. Especially among intracellular Ags, compartmentalized Ags appeared to be expressed at lower levels, as shown in the model of hen egg white lysozyme (6). Thus, the findings of previous experiments, most of which used peptide-pulsed APCs or mice bearing soluble/membrane-bound neo-self Ags, might be difficult to apply directly to understanding CD4 ϩ T cell tolerance to intracellular autoantigens.…”

“…These systemic autoimmune responses are driven by autoantigen-specific CD4 ϩ T cells (1,2). Although Ag compartmentation within cells could influence the processing and loading of antigenic determinants onto MHC molecules (3)(4)(5)(6), only a few studies have focused on the mechanism of T cell tolerance to nuclear autoantigens (7,8).…”