What is the interpretation of T and B Cells by Flow Cytometry, specifically the expression of antigens such as Cluster of Differentiation (CD) 3, CD4, CD8, and CD19, including normal versus abnormal expression patterns, such as dim or bright expression?

From the Guidelines

Flow cytometry is a crucial diagnostic tool for evaluating lymphocyte populations, and the T and B Cells by Flow Cytometry test specifically assesses cell surface markers to identify abnormalities in T and B cell subsets. The test typically reports both absolute counts (cells/μL) and percentages of lymphocyte subsets, including T cells (CD3+), helper T cells (CD3+CD4+), cytotoxic T cells (CD3+CD8+), and B cells (CD19+) 1.

Key Components of the Test

• Absolute counts of T and B cells
• Percentages of lymphocyte subsets
• Antigen expression intensity (bright, dim, or negative)

Normal Expression Patterns

Normal expression patterns include:

• Bright CD3 on T cells
• Bright CD4 on helper T cells
• Bright CD8 on cytotoxic T cells
• Bright CD19 on B cells

Abnormal Findings

Abnormal findings might include:

• Dim CD3 expression (seen in some T-cell leukemias) 1
• Aberrant co-expression (like CD4 and CD8 together)
• Absence of expected markers
• Abnormal expression intensity, like dim CD3 in T-cell large granular lymphocytic leukemia, can indicate malignancy
• Loss of CD7 expression on T cells may suggest T-cell lymphoma

Interpretation

The interpretation requires comparing both numerical values and expression patterns to established reference ranges, with consideration of the clinical context 1.

Clinical Context

Abnormalities in either count or expression intensity can indicate primary immunodeficiencies, malignancies, or other immune system disorders. For example, in Common Variable Immunodeficiency, you might see normal T cell counts but decreased B cell (CD19+) numbers. In HIV infection, CD4+ T cells are typically decreased.

Antigen Expression

The levels of surface immunoglobulin, CD20, and CD79b are characteristically low compared with those found on normal B cells in certain conditions like chronic lymphocytic leukemia (CLL) 1. In CLL, the leukemia cells co-express the T-cell antigen CD5 and B-cell surface antigens CD19, CD20, and CD23. Each clone of leukemia cells is restricted to expression of either κ or λ immunoglobulin light chains. The T and B Cells by Flow Cytometry test is essential for diagnosing and monitoring various immune system disorders, and its interpretation requires a comprehensive understanding of normal and abnormal expression patterns.

From the Research

Overview of Flow Cytometry

Flow cytometry is a laboratory technique used to analyze and sort cells based on their physical and chemical properties. In the context of T and B cell analysis, flow cytometry is used to identify and quantify different cell populations, including CD3+, CD4+, CD8+, and CD19+ cells [ 2 ].

T and B Cell Markers

The following markers are commonly used to identify T and B cells:

• CD3: a marker for all T cells
• CD4: a marker for helper T cells
• CD8: a marker for cytotoxic T cells
• CD19: a marker for B cells These markers can be used to identify different cell populations and to determine their activation status [ 3 ].

Interpretation of Lab Results

The lab report for T and B cell analysis by flow cytometry typically includes numerical data, such as:

• Absolute counts (e.g., CD3+ cells/μL)
• Percentage of total lymphocytes (e.g., CD4+ cells/%) The report may also include information on the expression of specific markers, such as:
• CD3 dim or bright: indicating the level of CD3 expression on T cells
• CD4 or CD8 dim or bright: indicating the level of CD4 or CD8 expression on T cells
• CD19 dim or bright: indicating the level of CD19 expression on B cells Normal versus abnormal expression of these markers can vary depending on the individual and the specific clinical context [ 4 ].

Abnormalities to Look for

Abnormalities in T and B cell populations can include:

• Low absolute counts or percentages of specific cell populations (e.g., CD4+ cells)
• Abnormal expression of specific markers (e.g., CD3 dim on T cells)
• Presence of abnormal cell populations (e.g., CD19+ cells with abnormal CD19 expression) These abnormalities can be indicative of various immune disorders or diseases, such as immunodeficiencies or lymphoproliferative disorders [ 5 ].

Example of Specific Testing

For example, a lab report for T and B cell analysis by flow cytometry may include the following results:

• CD3+ cells: 1000 cells/μL (normal range: 500-2000 cells/μL)
• CD4+ cells: 40% of total lymphocytes (normal range: 30-50%)
• CD8+ cells: 20% of total lymphocytes (normal range: 15-30%)
• CD19+ cells: 10% of total lymphocytes (normal range: 5-15%)
• CD3 expression: bright on 90% of CD3+ cells (normal range: 80-100%)
• CD4 expression: bright on 80% of CD4+ cells (normal range: 70-90%)
• CD8 expression: bright on 70% of CD8+ cells (normal range: 60-80%)
• CD19 expression: bright on 80% of CD19+ cells (normal range: 70-90%) These results would be considered normal, but abnormalities in any of these parameters could indicate an underlying immune disorder or disease [ 6 ].