Lysosomal compartment in antigen-presenting cells (MIIC) (MIIC)

The lysosomal compartment in antigen-presenting cells (APCs) is a specialized acidic organelle critical for the processing and presentation of exogenous antigens to the adaptive immune system (Roche & Furuta, Nature Reviews Immunology, 2015). In cells such as dendritic cells, macrophages, and B cells, this compartment—often referred to as the MHC class II compartment (MIIC)—contains the enzymatic machinery, including cathepsins, required to proteolytically degrade proteins into immunogenic peptides (Watts, Current Opinion in Immunology, 2012). These peptides are loaded onto MHC class II molecules, a process facilitated by the chaperone HLA-DM, before the complex is trafficked to the plasma membrane for CD4+ T cell activation (Mellman & Steinman, Nature, 2001). Dysregulation of lysosomal function or antigen processing is implicated in various autoimmune diseases, where self-antigens are inappropriately presented, leading to chronic inflammation (Schrezenmeier & Dörner, Nature Reviews Rheumatology, 2020). Therapeutic strategies often involve lysosomotropic agents, such as hydroxychloroquine, which accumulate in these compartments, raise the internal pH, and inhibit the activity of pH-dependent proteases and Toll-like receptors (TLRs) (Ohkuma & Poole, PNAS, 1978). By modulating the lysosomal environment, these drugs effectively dampen the activation of the immune system in conditions like systemic lupus erythematosus and rheumatoid arthritis (StatPearls, Hydroxychloroquine, 2023). While not a single molecular target, the lysosomal compartment represents a vital functional hub for controlling immune signaling and antigen recognition.

Other names

LysosomeMHC class II compartmentMIICEndolysosomal systemAntigen-processing compartment

Inhibition of antigen processing and presentation via lysosomal pH elevation and protease inhibition.