[Laboratory tests for cellular immunology: flow cytometric analysis of lymphocyte subsets]

Flow cytometric analysis for lymphocyte subsets provides two kinds of data: proportion of fluorescence-positive cells (lymphocyte subsets) and the fluorescence intensity. For proportional analysis of lymphocyte subsets, lymphocytes are fractionated with a conventional gate window in scatter analysis, but if activated or enlarged lymphocytes are examined, lymphocytes should be fractionated with an extended gate window. On the other hand, fluorescence intensity of a lymphocyte subset, which represents density of cell surface antigen detected by fluorescence-conjugated specific antibody, is not measured in routine tests yet. However, data on fluorescence intensity are often more valuable than the proportions of lymphocyte subsets: e.g., decrease in fluorescence intensity, but not in proportion, of CD8+ cells in active Graves' disease, and marked decrease in fluorescence intensity of OKT4+ cells in a carrier of familial OKT 4 epitope deficiency. Furthermore, two-color flow cytometry has enabled to measure more valuable, classified subsets of lymphocytes than single color flow cytometry. For example, measurement of peripheral CD5 (Leu-1)+ B cells is very useful for diagnosis of Graves' disease and its differentiation from destruction-induced thyrotoxicosis. In conclusion, we showed that measurement of fluorescence intensity of lymphocyte subsets and two-color flow cytometry are useful for laboratory tests of lymphocyte subsets.