Induction of homotypic lymphocyte aggregation: Evidence for a novel activation state of the β1 integrin

Sriram Neelamegham, Scott I. Simon, Bradley W. McIntyre, Kyriacos Zygourakis

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9 Scopus citations


Intercellular adhesion of Jurkat lymphocytic cells was investigated by use of monoclonal antibodies 33B6 and 18D3, which bind to the β1 integrin receptor. 33B6 induced homotypic aggregation of Jurkat cells, whereas 18D3 inhibited this aggregation. Jurkat cells could be induced to aggregate at low 33B6 concentrations corresponding to 5% β1 integrin site occupancy, and the rate of aggregation was maximum at 30% occupancy. Simultaneous addition of mAb 18D3 and 33B6 demonstrated that the two antibodies mediate changes in the β1 integrin activation state that are competitive in nature. Aggregation through β1 integrin induced by 33B6 was reversed by subsequent addition of 18D3. To further examine the mechanism by which 33B6 and 18D3 affect cell adhesion function, we explored the binding of monoclonal antibody (mAb) 15/7. This mAb recognizes an activation epitope of the β1 integrin and has been shown to sustain cell adhesion to vascular cell adhesion molecule 1 (VCAM-1) and fibronectin. Activation of Jurkat cells with Mn2+ caused a 2.5-fold increase in 15/7 binding but did not increase binding of 33B6. 33B6 partially blocked 15/7 binding to β1 integrin on unstimulated and Mn2+-activated Jurkat cells. 18D3 did not affect mAb 15/7 binding. These results indicate that 33B6 and 18D3 modulated homotypic aggregation by inducing a novel activation state of the very late activation integrin distinct from the state recognized by 15/7, which supports cell binding to VCAM-1 and fibronectin.

Original languageEnglish (US)
Pages (from-to)872-882
Number of pages11
JournalJournal of Leukocyte Biology
Issue number6
StatePublished - Jun 1996
Externally publishedYes


  • Adhesion
  • Mechanism
  • Very late activation integrin

ASJC Scopus subject areas

  • Cell Biology


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