In
immunology
Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see ther ...
, agranulocytes (also known as nongranulocytes or mononuclear leukocytes) are one of the two types of
leukocytes (white blood cells), the other type being
granulocyte
Granulocytes are
cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear. They ha ...
s. Agranular cells are noted by the absence of
granules in their
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...
, which distinguishes them from granulocytes. The two types of agranulocytes in the
blood circulation
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...
are
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adap ...
s and
monocytes. These make up about 35% of the
hematologic blood values.
The distinction between granulocytes and agranulocytes is not useful for several reasons. First, monocytes contain granules, which tend to be fine and weakly stained (see
monocyte entry). Second, monocytes and the granulocytes are closely related cell types developmentally, physiologically and functionally. Third, this distinction is not used by haematologists; it is an erroneous separation that has no meaning.
Lymphocytes are much more common in the
lymphatic system and include
natural killer T-cells. Blood has three types of lymphocytes:
B cells
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...
,
T cells and
natural killer cells (NK cells). B cells make antibodies that bind to
pathogens to enable their destruction.
CD4+ (helper) T cells co-ordinate the
immune response (they are what becomes defective in an
HIV infection).
CD8+ (cytotoxic) T cells and
natural killer cells are able to kill cells of the body that are infected by a virus. T cells are crucial to the immune response because they possess a unique
'memory' system which allows them to remember past invaders and prevent disease when a similar invader is encountered again.
Monocytes share the
phagocytosis function of
neutrophils
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying i ...
, but are much longer lived as they have an additional role: they present pieces of pathogens to T cells so that the pathogens may be recognized again and killed, or so that an antibody response may be mounted. Monocytes are also known as
macrophages after they migrate from the bloodstream and enter tissue.
The granulocytes are
neutrophils,
eosinophils
Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. ...
,
basophil
Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. However, they are the largest type of granulocyte. They are responsible for inflammator ...
s, and
mast cell
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a pa ...
s.
Infiltrate
''Mononuclear cell infiltrates'' are characteristic of
inflammatory lesions, where white blood cells, mainly
macrophages and
lymphocytes, collect at the site of injury to help clear away the debris.
It is the sign of onset of
graft rejection.
Additional images
Image:Illu blood cell lineage.jpg, Blood cell lineage
References
{{Blood
Leukocytes