Final answer:
In newborns, lymphocytes are primarily T cells, which are involved in the cell-mediated immune response.
Step-by-step explanation:
In newborns, lymphocytes are primarily T cells. T cells are a type of lymphocyte that make up approximately 80 to 90 percent of lymphocytes in human circulating blood. They are involved in the cell-mediated immune response, which helps protect against pathogens.