The major histocompatibility complex (MHC), or human leukocyte antigen (HLA) complex in humans, and H2 complex in mice, plays a vital role in immune responses. It encodes class I, class II, and class III regions, each with specific functions. Highly polymorphic, it contributes to diverse immune responses and susceptibility to diseases.

Proteins undergo degradation through the ubiquitin-proteasome system (UPS) via ubiquitination, where ubiquitin is attached to target proteins. Specific enzymes (E1, E2, E3) are involved in this process. Proteins marked with polyubiquitin chains are recognized and degraded by the proteasome, leading to the generation of small peptides with various cellular fates.

The maturation process of phagosomes and endosomes involves several crucial steps, including early endosome formation, maturation to late endosomes, cargo sorting, recycling, degradation, fusion with lysosomes, membrane trafficking, and exit from the endosomal system. These steps are essential for cellular homeostasis, signaling regulation, and efficient material processing.