Internalization and degradation of anti-CD4 monoclonal antibodies bound to human peripheral blood lymphocytes

• Published in: Molecular immunology Vol. 30; no. 7; p. 649
• Main Authors: Morel, P, Vincent, C, Wijdenes, J, Revillard, J P
• Format: Journal Article
• Language: English
• Published: England 01.05.1993
• Subjects: Antibodies, Monoclonal - metabolism; CD4 Antigens - metabolism; CD4-Positive T-Lymphocytes - immunology; CD4-Positive T-Lymphocytes - metabolism; Endocytosis; Humans; In Vitro Techniques
• ISSN: 0161-5890
• DOI: 10.1016/0161-5890(93)90076-N

Treatment of patients with anti-CD4 mAbs induces both functional alterations of CD4+ cells and depletion of circulating CD4+ lymphocytes. Some of these effects depend on the amount of mAb molecules bound per CD4+ cell and on the properties of the Fc part of the mAb (isotype specificity). We have investigated the fate of anti-CD4 monoclonal antibodies (mAbs) after their interaction with CD4 protein on the surface of peripheral blood lymphocytes (PBL). We used seven anti-CD4 mAbs whose epitope specificity, equilibrium constant and kinetics of binding are reported. Lymphocytes were saturated with anti-CD4 mAbs either at +4 degrees C or 37 degrees C then washed and incubated in antibody-free medium. At different time intervals cells were processed for analysis. By indirect immunofluorescence, it was shown that the amount of surface-bound mAb decreased rapidly when cells were incubated at 37 degrees C, but not at 4 degrees C. With 125I-mAbs, we demonstrate that there was a rapid internalization of the molecules followed by the re-expression on the cell surface of a part of initially bound mAbs and by the release of partially degraded antibody in the cell supernatant. In the presence of sodium azide (10 mM) only a slow dissociation of intact antibody occurred, without internalization. The radioactive material eluted in the 100-200 kDa zone from supernatants was only partly adsorbed on protein A and hardly on CD4+ cells, indicating that alterations of the Fc region and loss of antigen binding activity, possibly by formation of CD4-anti-CD4 complexes, had occurred during the process of internalization and release into the extracellular medium. These data may be important to consider for adjusting the dosage of anti-CD4 mAbs to be administered.