BACKGROUND: Quantitation of natural killer (NK) cells in benign and malignant effusions has yielded conflicting results in the past. Studies have claimed higher, lower, and essentially equal percentages of NK cells for benign and malignant effusions. In addition, virtually no literature exists on the numbers and distribution of T lymphocytes expressing T-cell receptor alpha/beta (TCR alpha/beta) and T-cell receptor gamma/delta (TCR gamma/delta) in body effusions.

METHODS: Using multicolor flow cytometry and sequential gating techniques, NK cells and T lymphocytes expressing TCR alpha/beta and TCR gamma/delta were identified and quantitated in 30 benign and 30 malignant effusions.

RESULTS: No significant difference in percentage of NK cells was found between benign and malignant effusions. The absolute number per miroliter of CD16(+)CD56(+) NK cells was higher in malignant than in benign effusions, but only at a borderline level of statistical significance. T cells expressing TCR alpha/beta far outnumbered those expressing TCR gamma/delta in all effusions, a distribution similar to that in normal adult peripheral blood and lymphoid tissue. The percentages and absolute numbers of these T-cell subsets were the same in benign and malignant effusions.

CONCLUSIONS: Enumeration of NK cells and of T lymphocytes expressing TCR alpha/beta or TCR gamma/delta in human body effusions is not helpful in attempting to distinguish between benign and malignant effusions. Values for the two T-lymphocyte subsets in human effusions are, to our knowledge, established for the first time by flow cytometric determination.