High CD99 expression in memory T and B cells in reactive lymph nodes

Area of Science:

• Immunology
• Cell Biology

Background:

• CD99 is a cell surface glycoprotein involved in lymphocyte activation and T-cell receptor-mediated responses.
• Its expression patterns and role in differentiating lymphocyte subsets within human lymph nodes require further elucidation.

Purpose of the Study:

• To investigate the expression levels and distribution of CD99 on lymphocytes in hyperplastic perigastric lymph nodes.
• To determine the relationship between CD99 expression intensity and lymphocyte activation status.

Main Methods:

• Immunohistochemical analysis of CD99 expression in 35 hyperplastic perigastric lymph nodes.
• Three-color flow cytometric analysis using a panel of lymphocyte subset markers (CD3, CD4, CD8, CD19, CD23, CD45RA, CD45RO, CD69, CD138, IgM, IgD, IgG).

Main Results:

• All lymphocytes expressed CD99, with distinct CD99high and CD99low populations observed.
• CD99high cells were primarily located in paracortical and medullary cords, while CD99low cells were found in germinal centers.
• Flow cytometry identified CD99high cells as predominantly activated/memory T cells (CD4+CD45RO+), whereas CD4+CD45RA+ T cells were CD99low.
• Among B cells, IgG+ cells showed higher CD99 expression than IgM+ cells.

Conclusions:

• CD99 expression is heterogeneous among lymphocytes in hyperplastic lymph nodes.
• CD99 upregulation correlates with lymphocyte activation, particularly in memory T cells and IgG-expressing B cells.
• CD99 functions as a marker for recently activated lymphocytes.