Correlation between cell size and CD38 expression in chronic lymphocytic leukaemia

Both CD38 expression and increased cell size are features of B-lymphocyte activation and have been implicated as adverse prognostic factors in B-cell chronic lymphocytic leukaemia (CLL). We therefore examined the relationship between these two variables by FACS analysis in 140 consecutive CLL patients. Using the mean forward-angle light scatter (FSC) as a measure of cell size, circulating B lymphocytes were found to be significantly larger in "CD38-positive" cases (those in which the antigen was expressed in at least 20% of the malignant cells) as compared with "CD38-negative" patients (p = 0.029). Furthermore, within individual cases B lymphocytes expressing CD38 were, on average, significantly larger than cells that did not express the antigen (p < 0.0001). Finally, when B lymphocytes of individual "CD38-positive" cases were arbitrarily divided into large and small subpopulations using their mean FSC as a cut-off, CD38 was found to be more frequently expressed on the larger cells (p < 0.0001). This strong positive correlation between CD38 expression and cell size implicates cell activation as a possible underlying determinant of both tumour-cell phenotype and clinical outcome in CLL.