Final answer:
Helper T cells are the lymphocytes that bridge the cellular and humoral immune responses by aiding in activating B cells to produce antibodies, as well as stimulating cell-mediated responses.
Step-by-step explanation:
The lymphocytes that act as the bridge between the cellular and humoral responses are the helper T cells. Specifically, the class known as Th2 helps with the humoral immune response by secreting cytokines that assist B cells in their production of antibodies. Helper T cells play a critical role in both activating antibody production (part of the humoral response) and stimulating the cell-mediated immune response. Contrary to helper T cells, cytotoxic T cells are primarily involved in directly attacking cells that have been infected by pathogens. Regulatory T cells are mainly engaged in maintaining immune response balance to prevent overactivity that might lead to autoimmune disorders.