This scanning electron micrograph shows a T lymphocyte, which is responsible for the cell-mediated immune response. The spike-like membrane structures increase surface area, allowing for greater interaction with other cell types and their signals. As explained in Overview of Specific Adaptive Immunity , the antibodies involved in humoral immunity often bind pathogens and toxins before they can attach to and invade host cells. Thus, humoral immunity is primarily concerned with fighting pathogens in extracellular spaces.
Introduction to T and B lymphocytes - Autoimmunity - NCBI Bookshelf
T cell , also called T lymphocyte , type of leukocyte white blood cell that is an essential part of the immune system. T cells are one of two primary types of lymphocytes — B cells being the second type—that determine the specificity of immune response to antigens foreign substances in the body. T cells originate in the bone marrow and mature in the thymus. In the thymus, T cells multiply and differentiate into helper , regulatory , or cytotoxic T cells or become memory T cells. They are then sent to peripheral tissues or circulate in the blood or lymphatic system.
NCBI Bookshelf. New York: Garland Science; The greater part of lymphocyte development in mammals occurs in the specialized environments of the central lymphoid organs—the bone marrow and the liver in the fetus for B cells and the thymus for T cells.
A T cell is a type of lymphocyte which develops in the thymus gland and plays a central role in the immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor on the cell surface. These immune cells originate as precursor cells , derived from bone marrow ,  and develop into several distinct types of T cells once they have migrated to the thymus gland - for which these cells are named. T cell differentiation continues even after they have left the thymus. Groups of specific, differentiated T cells have an important role in controlling and shaping the immune response by providing a variety of immune-related functions.