![Fig. 1. Engagement of the extracellular domain of the CD34 antigen induces homotypic adhesion. / (A) Adhesion is epitope class–specific: Monoclonal antibodies recognizing class I and II, but not class III, CD34 epitopes induce cell-cell adhesion. KG1a cells (0.7 × 106-1.0 × 106 cells/mL) were stimulated with 15 μg/mL IgG1 monoclonal antibody for 30 minutes at 37°C. Engagement of CD34 class I (with HPCA-1 [My10]) or class II epitopes (with QBEND 10) strongly induced homotypic adhesion of KG1a cells. Engagement of class III epitope (with 581) had no effect. (B) Cell-cell adhesion can be competitively inhibited by CD34 peptide. Prior to adhesion assays, cells in the right panel were pretreated for 30 minutes with 250 μg/mL blocking peptide (Stem Cell Releasing Peptide [9069N]). Each cell sample then received 15 μg/mL 9C5 antibody, and adhesion assays were carried out as in panel A. The 9C5 peptide mimics amino acids 14 to19 of the mature CD34 antigen. At this concentration, cell-cell adhesion was entirely inhibited. At 50 μg/mL, approximately 50% inhibition was observed (data not shown).](https://ash.silverchair-cdn.com/ash/content_public/journal/blood/97/12/10.1182_blood.v97.12.3768/6/h81211161001.jpeg?Expires=1735580796&Signature=EHbwRTtticFZl2FLH4AJw9Ho1-yyg6u73qGyUyjmg54HTlG0g-y~ryF6xmOYGe8CsL1VyPWb9hCDbZz0ALf52WBDmMP-KeHODLr9MZMQ7SdoMv6iHaiF~V52uCtXCLOclBMn1iO0ppc9ilM67BIpm2-Ms1UttQFs-T7m7uF7vxiTqqDYTl1hqAcenP3~CuRuvSQTgXumq-IkRSEyqlYqiA3gd25F9U9jYctDcZqxXLu5KR9dhEZGHsVE6lnbnzd5AOSnbugH0zzz1Yj2lkrMHLIetXJG0BKs-S1XgipNpmpI~wtUS-0d16u0o~eH--fb1h1Rg5wvny3JJ0ykHsa7Jg__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Engagement of the extracellular domain of the CD34 antigen induces homotypic adhesion.
(A) Adhesion is epitope class–specific: Monoclonal antibodies recognizing class I and II, but not class III, CD34 epitopes induce cell-cell adhesion. KG1a cells (0.7 × 106-1.0 × 106 cells/mL) were stimulated with 15 μg/mL IgG1 monoclonal antibody for 30 minutes at 37°C. Engagement of CD34 class I (with HPCA-1 [My10]) or class II epitopes (with QBEND 10) strongly induced homotypic adhesion of KG1a cells. Engagement of class III epitope (with 581) had no effect. (B) Cell-cell adhesion can be competitively inhibited by CD34 peptide. Prior to adhesion assays, cells in the right panel were pretreated for 30 minutes with 250 μg/mL blocking peptide (Stem Cell Releasing Peptide [9069N]). Each cell sample then received 15 μg/mL 9C5 antibody, and adhesion assays were carried out as in panel A. The 9C5 peptide mimics amino acids 14 to19 of the mature CD34 antigen. At this concentration, cell-cell adhesion was entirely inhibited. At 50 μg/mL, approximately 50% inhibition was observed (data not shown).
