Cells of the immune system are highly motile and use chemotaxis in navigating to and within different regions of the body. Communication between B cells and T cells is needed for antibody production and in the deployment of armed T cells to sites of infection. During development, immature immune cells must also find their way from their site of origin toward peripheral lymphoid organs.
Using two-photon microscopy of lymph nodes, Okada et al. followed the fate of antigen-specific B cells. After activation, the cells within the follicular B cell zone awoke from a relatively sluggish, random motion and began to steer a steady course toward the neighboring region of the lymph node containing T cells. This process depended on the surface chemokine receptor CCR7, linking the gradient of the chemokine CCL21 within the follicle to the directional behavior. Once inside the T cell zone, B cells coupled with T cell partners in a multidirectional dance, with the B cells appearing to take the lead.
In a study of developing T cells within the thymus, Witt et al. observed that thymocytes located within the cortical region altered their behavior after they had undergone positive selection. Similarly to follicular B cells, selected thymocytes switched from a random walk to directed migration toward the thymic medulla, through which they transit as they exit the thymus. Again, this suggests that long-distance cues induce the urge to travel in newly selected T cells. -- SJS
PLoS Biol. 3, e150; e160 (2005).
