Lymphocyte activation is thus associated with a number of alterations each of which might serve to transmit the signal from the exterior to the interior of the cell. However, as can be gleaned from this brief discussion, many of these alterations are intimately related and it is most likely that the ultimate biochemical pathway or pathways for activation will be a combination of many of the changes. It is important to note that, although the actual pathway or pathways have not been clearly delineated, the evidence to date does allow us to devise ways of manipulating lymphocyte activation and in so doing to manipulate the immune response. It also allows one to compare the known steps in the sequence in lymphocytes activated by mitogenic lectins and other cells activated by specific agents. It is interesting that a perusal of the other articles in this series will demonstrate that many of the changes seen in the lymphocyte are seen in other activation systems and suggests that the means of activating a cell are common, but that the result of the activation is cell dependent.