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Published on: January 3, 2013
In situ expression of B7/BB1 on antigen-presenting cells and activated B cells: an immunohistochemical study
P Vandenberghe1, J Delabie, M de Boer
1Department of Internal Medicine and Pathophysiology, University of Leuven, Belgium.
Insights
The B7/BB1 molecule, a T cell co-stimulatory ligand, is expressed on various immune cells, including dendritic cells and B cells. Its presence in fetal thymus suggests a role in thymocyte development.
Area of Science:
- Immunology
- Cell Biology
Background:
- B7/BB1 is a key ligand for CD28, a T lymphocyte receptor involved in immune responses.
- CD28 ligation by B7/BB1 enhances cytokine production and prevents T cell anergy.
- Previous studies indicated B7/BB1 expression on dendritic cells, activated B cells, and monocytes.
Purpose of the Study:
- To investigate the in situ expression and tissue distribution of B7/BB1.
- To elucidate the role of B7/BB1 in T cell activation and thymocyte maturation.
Main Methods:
- Immunohistochemistry using a novel monoclonal antibody (mAb B7-24).
- Analysis of tissue samples including skin, lymph nodes, spleen, and thymus.
Main Results:
- Strong B7/BB1 expression was observed on dendritic cells in various tissues (Langerhans cells, veiled cells, interdigitating dendritic cells).
- B7/BB1 was present on fetal thymus dendritic cells but absent in adult thymuses.
- Expression was also noted on a subset of B immunoblasts and germinal center B cells, and on macrophages/epithelioid cells in granulomatous inflammation.
Conclusions:
- Tissue distribution of B7/BB1 supports its co-stimulatory role in T cell activation in vivo, particularly on professional antigen-presenting cells.
- The presence of B7/BB1 in the fetal thymic medulla suggests a role in thymocyte development and maturation.
Abstract:
B7/BB1 is a physiological ligand for CD28, a receptor expressed on a major subset of T lymphocytes. B7/BB1 has been shown to be expressed on human blood dendritic cells and on in vitro activated (but not resting) B cells and monocytes. Ligation of CD28 with B7/BB1 up-regulates cytokine production and prevents the induction of anergy in T cells activated through TCR/CD3. We examined the in situ expression of B7/BB1 by immunohistochemistry with a novel mAb B7-24. Dendritic cells in skin (Langerhans cells), lymph node sinuses (veiled cells), and T cell zones of spleen and lymph nodes (interdigitating dendritic cells) were strongly positive for B7/BB1. B7/BB1 was also present on fetal thymus dendritic cells located at the cortico-medullar junction and the medulla, but absent in normal adult thymuses. Resident macrophages and endothelial cells did not stain, but in granulomatous inflammations B7/BB1 was found on macrophages and epitheloid cells. A subset of B immunoblasts and of germinal center B cells in lymph node and spleen was also found to express B7/BB1. Our findings on the distribution of B7/BB1 expression in tissues, in particular its expression on professional antigen-presenting cells, further substantiate the putative co-stimulatory role of B7/BB1 in T cell activation in vivo. The presence of B7/BB1 in fetal but not adult thymic medulla suggests a role for B7/BB1 in thymocyte maturation.
