Treg clonality and function. (A) Spectratype analysis of a representative ITP patient prior to ritucximab therapy. The normal TCR VB spectratype pattern consists of 5 to 8 bands and shows a Gaussian distribution in which the density of bands is generally higher in the middle part of the spectratype. Contracted spectratypes consisting of 1 to 4 peaks suggest the presence of a monoclonal (1 dominant peak) or oligoclonal (2-4 peaks) T-cell population. In this case almost all patterns appear polyclonal. (B) Suppressive function of Tregs in ITP. The suppressive function of CD4⁺CD25⁺ T cells isolated from the peripheral blood of patients with idiopathic thrombocytopenic purpura in active phase was decreased compared with normal controls, but was restored to normal values in those responding to rituximab. The results are expressed as the percentage of cell proliferation, according to the following formula: percent cell proliferation = (counts per minute of CD4⁺CD25⁻ plus CD4⁺CD25⁺ cells/cpm of CD4⁺CD25⁻ cells alone) × 100. Pre indicates pretreatment; R, responders; and NR, non responders. The central horizontal bar is the median and the top and bottom bars indicate the SD.