Synthetic peptides of human CD4 enhance binding of Ig to monocyte/macrophage cells. I. Characterization and mapping studies.
Human T cell glycoprotein CD4 binds to class II MHC molecules and to HIV envelope protein gp120. We have shown that CD4 and synthetic peptides corresponding to amino acid residues 21-49 of the first extracellular domain of CD4, also bind Ig and, with greater avidity, antibody:Ag complex. We investigated the effect of CD4 synthetic peptides on the binding and uptake of human Ig by monocyte/macrophage U937 cells. We found that a synthetic peptide corresponding to amino acid residues 21-49 enhanced binding to U937 cells of both aggregated and nonaggregated Ig. The enhancement was concentration dependent, occurred both in normal and low ionic strength conditions, and varied with the time and the temperature of the preincubation step. The enhancement was maximal after preincubation for 3 h at 37 degrees C. A peptide concentration of 20 micrograms/ml was sufficient for optimal binding of both nonaggregated and aggregated Ig. CD4 peptide 21-49 also enhanced binding of Ig to Staphylococcus aureus protein A. These studies open a new perspective in the way monocyte/macrophage cells handle Ig, antibody:Ag or Id:anti-Id complex, in particular when present at threshold amounts in a nonprecipitating form.
Lenert
P
P
Department of Medicine, University of California, San Diego 92103.
Mehta
R L
RL
Zanetti
M
M
D000595:Amino Acid Sequence; D000936:Antigen-Antibody Complex / Q000378:metabolism; D001692:Biological Transport; D015704:CD4 Antigens / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D066298:In Vitro Techniques; D008264:Macrophages / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism*; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013205:Staphylococcal Protein A / Q000378:metabolism; D013329:Structure-Activity Relationship; D013696:Temperature; D013997:Time Factors
D000936:Antigen-Antibody Complex; D015704:CD4 Antigens; D007136:Immunoglobulins; D010446:Peptide Fragments; D013205:Staphylococcal Protein A