#00061542

These flow cytometry plots, corresponding to the same specimen, are both gated for lymphocytes (typically bright CD45, low side scatter). The first plot shows CD3 versus CD5, and the second shows CD8 versus CD4. In the first plot, the blue cells do express CD3, but show minimal to absent CD5 expression. The green and red cells express CD3 as well as some CD5. Lastly, the purple cells express neither CD3 nor CD5. In the second plot, the green cells express CD8 but not CD4, and conversely, the red cells express CD4 but not CD8. The blue and purple cells both lack expression of CD8 and CD4. Therefore, the green cells express CD3, CD5, and CD8, consistent with cytotoxic T lymphocytes, while the red cells express CD3, CD5, and CD4, consistent with helper T cells. The purple cells express virtually no CD3, CD5, CD4, or CD8, consistent with B lymphocytes. The blue cells, however, express CD3, and express minimal to absent CD5, but express no CD4 or CD8. This expression profile is consistent with a T lymphocyte population, with possibilities including gamma-delta T lymphocytes or malignant T lymphocytes with aberrant CD5 loss. Given the somewhat heterogeneous weak CD5 expression (minimal to absent), and concurrent lack of CD4 and CD8 expression, these blue cells are most consistent with gamma-delta T lymphocytes, which are resting mature T lymphocytes with putative roles in immune regulation and bridging between innate and adaptive immunity.