withoutid

1) I am not so sure but activated CD8 T cells do have cytoplasmic granules and they are not classified as granulocytes. 2) A naive CD8 T cell must be activated by professional APC to undergo clonal expansion and gain effector state. Professional APC not only present Ag but also co-stimulatory molecules to the T cell (CD80/CD86-->CD28, OX40L-->OX40). In this licensing step, the T cells must see at least 400 Ag/MHC on a single professional APC (http://www.pnas.org/content/111/35/E3679.long). Once CD8 T cell are licensed by APC (mostly dendritic cells), they can recognized and kill virus infected cells with even 1 Ag on MHCI. Cells other than professional APC don't express co-stimulatory to license the naive CD8 T cells. They have MHC class I for one purpose: be killed by cytotoxic T cells once they get infected by virus or intracellular bacteria. Like you said, cross-presentation is a mechansim to effeciently present Ag by APC even when they are not infected by virus.