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Changes in CD44 expression during B cell differentiation in the human tonsil
1Department of Clinical Immunology, Flinders Medical Centre.
Insights
CD44 cell surface glycoprotein expression changes during B cell differentiation, with levels varying from high on resting cells to low on activated blasts, and re-emerging on mature B cells.
Area of Science:
- Immunology
- Cell Biology
Background:
- CD44 is a cell surface glycoprotein involved in cell adhesion and signal transduction.
- Its role in B cell differentiation, particularly in secondary lymphoid tissues, is under investigation.
- Changes in CD44 expression may reflect evolving cellular requirements during B cell maturation.
Purpose of the Study:
- To investigate the expression pattern of CD44 during antigen-dependent B cell differentiation.
- To correlate CD44 expression levels with specific B cell differentiation markers.
Main Methods:
- Flow cytometry analysis of CD44 expression.
- Correlation with surface immunoglobulin (IgD, IgM, IgG, IgA) and differentiation markers (CD23, CD38).
Main Results:
- CD44 exhibits a trimodal expression pattern during B cell differentiation.
- High CD44 on resting IgD+/IgM+ cells; maintained at early CD23+ activation stage.
- CD44 downregulated on CD38+ blasts (centroblasts); re-expressed on centrocytes and post-germinal center B cells (IgG+/IgA+).
Conclusions:
- CD44 expression is dynamically regulated during B cell differentiation.
- The observed pattern suggests CD44's involvement in B cell homing, proliferation, and survival.
- Further studies are needed to elucidate the functional significance of CD44's dynamic expression in B cell development.
Abstract:
CD44 is a widely distributed cell surface glycoprotein that has been implicated in a number of cellular adhesion processes and signal transduction events. These functional capabilities qualify CD44 as a potential mediator of contact-signaling events underlying the process of antigen-dependent B cell differentiation in secondary lymphoid tissues. We postulated that changes in the expression of CD44 during B cell differentiation reflect the cells' changing requirements for this receptor. It has been reported that germinal center B cells are low to negative for CD44 expression, implying that the receptor is lost upon activation. Correlation of the expression of CD44 with surface immunoglobulin and a number of B cell differentiation markers revealed a trimodal expression pattern. High levels of CD44 are expressed on resting IgD+/IgM+ cells. The receptor is still expressed at the early activation stage defined by the expression of CD23. At the early blast stage, when the blast marker CD38 appears on the cell surface and IgD and CD23 disappear, CD44 is downregulated. The majority of CD38+/IgM+ blasts and CD38+/Ig- centroblasts are CD44 low/negative. The receptor is re-upregulated at the point of transition from the centroblast to the centrocyte level. Centrocytes expressing IgG or IgA comprise CD44high and CD44low fractions. IgG+ or IgA+ cells at the postgerminal center stage express high levels of CD44. The functional implications of this expression pattern are discussed.
