What do the different types of agranulocytes do?

Lymphocytes

One of the most important types of leukocytes in the human body, lymphocytes protect the body against serious infections. Lymphocytes are small and spherical in shape with very little cytoplasm and large nuclei. They form a lymphoid cell line within the bone marrow and circulate between the lymphatic system, tissues, and peripheral blood. There are three main types of lymphocytes – T cells, B cells, and natural killer cells. T cells and B cells provide specific immune responses while natural killer cells provide nonspecific immunity.

Monocytes

Monocytes play a key role in the immune response against bacterial infection. They belong to the myeloid cell line within the bone marrow and are found in abundance in the blood. These large-sized leukocytes have an amoeboid shape and a single, large nucleus that varies in shape but is usually kidney-shaped. Monocytes are circulating leukocytes. They remain in the blood for about eight hours before migrating to tissue, where they differentiate into either macrophages or dendritic cells. 

Macrophages

Macrophages are large, phagocytic cells that have a round, single-lobed nucleus. They play an important role in the immune system by acting as scavengers, destroying foreign organisms that enter the body by phagocytosis. Macrophages also secrete cytokines that activate and regulate the immune response.