Eosinophils: they have a bilobed nucleus and possess acid granulations in their cytoplasm. These granules contain hydrolytic enzymes and peroxidase, which a discharged into phagocytic vacuoles.

Eosinophils are more numerous in the blood during allergic diseases; they norma asent only – 3 % of leukocytes.

Basophils: they possess large spheroid granules, which are basophilic and metachromatic

Basophils degranulate in certain immune reaction, releasing heparin and histamine into their surroundings They also release additional vasoactive amines and slow reacting substance of anaphylaxis (SRS-A) consisting of leu-kotrienes LTC4, LTD4, and LTE4. They represent less than 1 % – of leukocytes

Agranulocytes are named according to their lack of specific granules. Lymphocytes are generally small cells measuring 7 – 10 mm in diameter and constitute 25–33 % of , leukocytes. They con tain circular dark-stained nuclei and scanty clear blue cyto plasm. Circulating lymphocytes enter the blood from the lymphatic tissues. Two principal types of immunocompetent lymphocytes can be identified T lymphocytes and В lymphocytes.

T cells differentiate in the thymus and then circulate in the peripheral blood, where they are the principal effec tors of cell-mediated immunity. They also function as helper and suppressor cells, by modulating the immune response through their effect on В cells, plasma cells, macrophages, and other T Cells.

В cells differentiate in bone marrow. Once activated by contact with an antigen, they differentiate into plasma cells, which synthesize antibodies that are secreted into the blood, intercellular fluid, and lymph. В lymphocytes also give rise to memory cells, which differentiate into plas ma cells only after the second exposure to the antigen. Monocytes vary in diameter from 15–18 mm and are the largest of the peripheral blood cells. They constitute 3–7 % of leukocytes.