CD23 is a protein found on the surface of some B cells and on a type of support cell inside lymph nodes called the follicular dendritic cell. Pathologists most often test for CD23 to help diagnose chronic lymphocytic leukemia and small lymphocytic lymphoma, and to separate them from other small-cell lymphomas. CD23 also helps the pathologist see the normal structure of a lymph node and tell whether a lymphoma has replaced it.
This article explains what CD23 is, which cells carry it, how pathologists use it to diagnose lymphoma, and what a CD23 result in your pathology report means.
CD23 is a protein that sits on the outer surface of certain immune cells. There, it helps B cells grow, respond to infections, and make antibodies. It acts as a receptor for IgE, the antibody type involved in allergic reactions. In normal tissue, several types of cells carry CD23:
Pathologists test for CD23 using immunohistochemistry, a test that uses antibodies to find specific proteins in a thin slice of tissue. Cells that carry CD23 turn brown under the microscope, usually along the outer edge of the cell. Laboratories can also measure CD23 on blood or bone marrow cells with flow cytometry, a common way to diagnose chronic lymphocytic leukemia.
CD23 helps diagnose lymphoma because different lymphomas made of small B cells show different CD23 results. Chronic lymphocytic leukemia and small lymphocytic lymphoma are the same disease, and the cancer cells are positive for CD23 in almost all cases. The pathologist usually evaluates CD23 along with CD5, CD20, and cyclin D1. Typical patterns include:
Distinguishing these lymphomas matters because each grows at a different pace and needs its own plan of care. A single CD23 result never makes the diagnosis by itself, so the pathologist combines it with the other markers and the appearance of the cells.
CD23 shows the structure of a lymph node by highlighting the web of follicular dendritic cells inside each follicle. In a normal or reactive lymph node, this web appears as neat, round patches. In some lymphomas, the pattern changes in ways that help the pathologist make a diagnosis:
Pathologists also use CD23 to help diagnose primary mediastinal large B-cell lymphoma, a fast-growing lymphoma that starts in the center of the chest. Many of these lymphomas are CD23-positive, which helps separate them from other types of diffuse large B-cell lymphoma. CD23 is also positive in some cases of follicular lymphoma that grow in a diffuse sheet rather than in follicles.
A CD23 result in your report describes whether the cells being studied carry this protein. Your report may describe the result in one of several ways: