Activation‐induced expression of MICA on T lymphocytes involves engagement of CD3 and CD28

MICA is an HLA‐related cell stress‐regulated antigen recognized by cytotoxic cells expressing the NKG2D molecule. Although resting lymphocytes do not express MICA, it can be induced on PHA‐activated T cells. Here, we demonstrate by Western blot that MICA is induced on allogeneic‐activated CD4 + and CD8 + T lymphocytes. Blocking activation with anti‐HLA class I, anti‐HLA‐DR, or anti‐CD86 mAb affected the expression of MICA slightly. When T cells were stimulated with anti‐CD3 or anti‐CD28 mAb plus PMA, a sustained up‐regulation of MICA was observed by Western blot, RT‐PCR, and flow cytometry. The expression of MICA reached a plateau at day 4 after CD3 engagement and at day 3 after anti‐CD28/PMA stimulation. Conversely, the proliferative response reached a peak at day 4. Hence, CD3 or CD28 engagement induces MICA expression on T lymphocytes. This activation‐induced expression might participate in NKG2D‐mediated cytotoxicity toward activated T cells to maintain homeostasis during an ongoing immune response.