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Published on: October 17, 2009
Expression of CD9 antigen on normal activated human B cells
1Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.
Insights
The CD9 antigen, associated with pre-B acute lymphoblastic leukemia (ALL), is expressed on activated tonsil B cells. Protein kinase C activation influences CD9 expression, but anti-CD9 antibodies do not affect B cell proliferation.
Area of Science:
- Immunology
- Cell Biology
Background:
- CD9 is an antigen associated with pre-B acute lymphoblastic leukemia (ALL).
- Understanding CD9 expression in normal B cells provides context for its role in leukemia.
Purpose of the Study:
- To investigate the expression of the CD9 antigen on normal activated B cells.
- To determine the role of protein kinase C (PKC) in regulating CD9 expression.
- To assess the functional impact of anti-CD9 antibodies on B cell activation.
Main Methods:
- Flow cytometry to analyze CD9 expression on tonsillar B cells.
- In vitro activation of B cells using various stimuli (PWM, TPA, anti-Ig, BCGF).
- Treatment with phorbol esters to investigate PKC involvement and anti-CD9 antibodies to study functional effects.
Main Results:
- CD9 expression was upregulated on activated tonsillar B cells, peaking at 4-6 days.
- CD9 expression correlated with protein kinase C activation, as shown by phorbol ester experiments.
- Anti-CD9 monoclonal antibody DU-ALL-1 did not inhibit or enhance B cell mitogenesis.
Conclusions:
- The CD9 antigen is present on a subset of activated normal tonsillar B cells.
- Protein kinase C activation is involved in the induction of CD9 expression.
- CD9 does not appear to play a direct role in regulating B cell proliferation in response to common activation signals.
Abstract:
The expression of the CD9 pre-B acute lymphoblastic leukemia (ALL)-associated antigen was studied. CD9-positive B cells were enriched in the in vivo-activated buoyant B cell population isolated from tonsils. Small tonsil B cells activated in vitro with either PWM, phorbol 12-myristate 13-acetate (TPA), or anti-Ig plus low Mr B cell growth factor (BCGF) also demonstrated increased CD9 expression. The peak of CD9 expression (30-40% positive cells) occurred after 4-6 days of activation. The kinetics of increased CD9 expression was similar to that of the 4F2 activation antigen. CD9 antigen expression on tonsillar B cells as well as on pre-B leukemic cell lines was associated with protein kinase C activation. Two phorbols that activate protein kinase C (TPA; phorbol 12,13-dibutyrate) induced expression of the CD9 antigen whereas a phorbol analogue that does not activate C kinase (4-alpha-phorbol 12,13-didecanoate) and an analogue that is a very weak agonist (phorbol 12-myristate 13-acetate-4-0-methyl ether) were unable to induce CD9 expression on tonsil B cells or on the cell lines. The effect of the anti-CD9 monoclonal antibody, DU-ALL-1, on B cell mitogenesis was studied. Dense or buoyant tonsillar B cells were cultured in the presence or absence of DU-ALL-1 antibody plus PWM, anti-Ig, and BCGF, DU-ALL-1 antibody did not inhibit or augment the mitogenic response of resting or activated B cells. These results indicate that the CD9 pre-B ALL antigen is present on a population of normal activated tonsillar B cells and that its induction of expression is associated with protein kinase C activation.
