Basophils

Basophils are the least numerous of the circulating leukocytcs, constituting 1% of the white blood cells of healthy adults. Like other white blood cells, basophils may leave the circulation, but they are capable of only very limited ameboid movement and phagocytosis in the tissues. Extravascular basophils are found most often at sites of inflammation and may be the major cell type at sites of cutaneous basophil hypersensitivity. Despite structural and functional similarities between basophils and mast cells, these cells are not the same and are distinguishable on the basis of ultrastructure. blood histology

Eosinophils

Eosinophils constitute only 1-4% of the circulating leukocytes in healthy adults. They may leave the bloodstream by diapedesis, spread out, and move about in the connective tissues. They are capable of only limited phagocytosis, showing a preference for antigen antibody complexes. The number of circulating eosinophils typically increases during allergic reactions and in response to parasitic infections and rapidly decreases in response to treatment with exogenous corticosteroids in blood.

2. Granulocytes have segmented nuclei and are described as polymorphonuclear leukocytes (PMNLs). Depending on the cell type, the mature nucleus may have 2-7 lobes connected by thin strands of nucleoplasm. Granulocyte types are most easily distinguished by their size and staining properties and by the appearance (as seen by EM) of the abundant specific granules in their cytoplasm. These granules are all membrane-limited and bud off the Golgi complex.

In addition to a small Golgi complex, each granulocyte contains a few mitochondria and free ribosomes and sparse RER. a. Neutrophils are the most abundant leukocytes in the blood. They usually constitute 60-70% of the white blood cells, with a limited range of normal variation (50-75%). They are also found outside the bloodstream, especially in loose connective tissue. Neutrophils are the first line of cellular defense against the invasion of bacteria. Once they leave the bloodstream, they spread out, develop ameboid motility, and become active phagocytes. Unlike lymphocytes, neutrophils are all terminally differentiated cells and so are incapable of mitosis.

Leukocytes

Leukocytes, or white blood cells, are nucleated and are larger and less numerous (6000-10,000/Cl) than erythrocytes.
Leukocytes can be divided into 2 main groups, granulocytes and agranulocytes, according to their content of cytoplasmic granules. Each group can then be further divided on the basis of size, nuclear morphology, ratio of nuclear to cytoplasmic volume, and staining properties. Two classes of cytoplasmic granules occur in leukocytes: specific and azurophilic granules. Specific granules are found only in granulocytes; their staining properties (neutrophilic, eosinophilic, or basophilic) distinguish the 3 granulocyte types. Azurophilic granules occur in both agranulocytes and granulocytes.
Their content of lytic enzymes suggests that they function as lysosomes. Unlike the RBCs, all leukocytes can leave the capillaries by squeezing between endothelial cells, a process termed diapedesis, and enter the surrounding connective tissue in response to infection or inflamma tion. The types and levels of activity expressed by extravascular leukocytes depend upon the specific cell type