Role of mitotic diffusion barriers in regulating the asymmetric division of activated CD8 T cells

Upon their activation, naive CD8 T cells divide and differentiate into short-lived effector cells, relevant for exerting immune control, and long-lived memory cells, relevant for long-term immunity. The proportion of memory cells generated depends highly on the context of activation and whether the activated cell divides symmetrically or asymmetrically. However, how T cells control the extent of their asymmetry during their first division in response to contextual signals is not known. Using fluorescence loss in photo-bleaching (FLIP) experiments, we show that the metabolic and plasma membrane asymmetry of mitotic T cells depend on the regulated assembly of a lateral diffusion barrier in their endoplasmic reticulum (ER-) membrane. In asymmetrically dividing T cells, the degrees of asymmetry correlated tightly to barrier strength, whereas symmetrically dividing T cells did not establish such a barrier. Direct positive or negative interference with barrier assembly enhanced or abrogated metabolic and plasma membrane asymmetry, respectively, indicating that barrier strength is a direct and decisive determinant of mitotic asymmetry. Thus, together our data identify diffusion barrier-mediated compartmentalization as a mechanism for how asymmetric T cell regulate their long-term response as a function of the activatory context.