Monovalent ligands of complement receptor 2 inhibit whereas polyvalent ligands enhance anti-Ig-induced human B cell intracytoplasmic free calcium concentration.
We have performed experiments to investigate the role of ligands for complement receptor 2 (CR2) in human B cell activation. Flow microfluorimetry was used to assess changes in free intracytoplasmic calcium concentration [Ca2+] in indo-loaded B cells, immediately after exposure to anti-mu antibody and to monovalent or polyvalent CR2 ligands. As monovalent ligands we used the C3d fragment and synthetic C3 peptides (peptides P14, residues 1201-1214, and P28, residues 1187-1214). As polyvalent ligands we used i) an intact monoclonal mouse anti-CR2 antibody (HB5) and its F(ab')2 fragment, ii) tetravalent P13 [residues 1202-1214) 4-template), and iii) P28 conjugated to BSA (molar ratio 5/1). Anti-CR2 antibody HB5, tetravalent P13, and P28 conjugated to BSA, enhanced the ability of F(ab')2 fragments of the IgG fraction of goat anti-human mu antibody to increase human B cell [Ca2+]i. In contrast, the monomeric CR2 ligands C3d and P28 inhibited the anti-mu-induced increase in human B cell [Ca2+]i. Multivalent P13, P28, and the HB5, by themselves, did not affect B cell [Ca2+]i. These experiments suggest that the valence of the CR2 ligands is crucial for the nature (synergistic vs antagonistic) of the message transmitted through the CR2.
Tsokos
G C
GC
Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
Lambris
J D
JD
Finkelman
F D
FD
Anastassiou
E D
ED
June
C H
CH
D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D008213:Lymphocyte Activation; D011940:Receptor Aggregation; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D011951:Receptors, Complement / Q000502:physiology*; D017464:Receptors, Complement 3d; D015398:Signal Transduction
D000944:Antigens, Differentiation, B-Lymphocyte; D008024:Ligands; D011947:Receptors, Antigen, B-Cell; D011951:Receptors, Complement; D017464:Receptors, Complement 3d; D002118:Calcium