Abnormal CD69 upregulation upon TCR activation 2017-08-12T19:45:57Z This feature can be measured by flow cytometry. Any abnormality in the upregulation of CD69 on T cells after activation via the T cell receptor (TCR). Upregulation of CD69 is one of the earliest and most sensitive measures of antigen recognition in the periphery, and transient expression of CD69 is associated with positive selection in the thymus. Abnormal T cell activation