B and T-lymphocytes are immune cells found in the white pulp of the spleen. T-lymphocytes are in charge of cell-mediated immunity, which is an immunological response that requires the activation of certain immune cells in order to combat infection. B-lymphocytes are responsible for producing antibodies that fight off foreign particles such as bacteria or viruses. The white pulp contains the largest number of lymphocytes in the spleen. Lymphocytes account for about 95% of all splenocyte cells. The remaining 5% consist of red blood cells, platelets, and small numbers of neutrophils and macrophages. The white pulp is divided into zones with different functions: the periarterial zone, the perivenous zone, and the marginal zone. The periarterial zone lies adjacent to the arterial supply of the spleen and is where most of the B-lymphocytes are found. The perivenous zone surrounds the venules that lead away from the central artery. This is where most of the T-lymphocytes are located. The marginal zone is the transition zone between the periarterial and perivenous zones. It contains many lymphoid follicles that are areas where B-cells can interact with their targets. Lymphocytes enter the spleen through special channels called sinuses. These channels are so named because they resemble the holes in a sieve.