Two types of polyubiquitin-reactive cytoplasmic bodies, particulate cytoplasmic structures (PaCS) and dendritic cell (DC) aggresome-like induced structures (DALIS), were analyzed by electron microscopy, immunocytochemistry, immunoblotting, and flow cytometry in DC obtained from human blood monocytes incubated with GM-CSF plus IL-4 (IL4-DC), GM-CSF plus IFNα (IFN-DC), or GM-CSF alone (GM-DC), with or without LPS maturation. PaCS developed as monomorphic aggregates of proteasome-reactive barrel-like particles only in ribosomes-rich cytoplasmic areas of differentiating IL4-DC. In contrast, DALIS formed as vesicular bodies storing K63-linked ubiquitinated proteins by coalescence of increased endosomal structures, in IFN-DC or after LPS maturation of GM-DC. DALIS-forming cells showed incomplete morphological and functional DC-type differentiation when compared to PaCS-forming IL4-DC. PaCS and DALIS may have different function as well as different origin and cytochemistry. DALIS may be a transient accumulation site of potentially antigenic polyubiquitinated proteins during their processing and presentation. PaCS are found under physiologic or pathologic conditions associated with increased/deranged protein synthesis and increased ubiquitin-proteasome activity. Given its high heat-shock protein content PaCS may work as a quality control structure for newly synthesized, cytosolic proteins. This comparative analysis suggests that PaCS and DALIS have distinctive roles in DC.
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