L. Santoro et al., MAJOR INVOLVEMENT OF CATHEPSIN-B IN THE INTRACELLULAR PROTEOLYTIC PROCESSING OF EXOGENOUS IGGS IN U937 CELLS, Molecular immunology, 30(11), 1993, pp. 1033-1039
Monoclonal antibodies used for diagnostic and therapeutic purposes beh
ave as antigens when injected into patients. They are recognized by T
cells in a processed form and in a major histocompatibility complex cl
ass II restricted fashion. Monoclonal murine IgG2a were used as a mode
l to analyse the early phase of antigen processing in U937 cells. IgG2
a prebound to cell surface Fc receptors were rapidly internalized in t
he cells. During internalization, they were proteolysed with a time-de
pendent intracellular accumulation of 26, 25, 24, 22 and 14 kDa fragme
nts. Comparison of in vitro IgG2a proteolysis by U937 subcellular frac
tions or by purified cathepsin B and their intracellular processing in
dicated that a major cathepsin B like protease is responsible for IgG2
a intracellular processing in endo-lysosomal compartments of U937 cell
s.