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Immunology Notes
Part 2: The Cells
I.
Cells of the immune system
A. Monocytes:
 Large amount of cytoplasm in relation to the nucleus
 Shape is variable
1. many are round
2. some have blunt pseudopods
3. may see phagocytized erythrocytes, leukocytes,
nuclei, cell fragments, pigment, bacteria, and
fungi in digestive vacuoles
4. nuclei are usually round or kidney shaped, but
may be deeply indented or have two or more
lobes separated by narrow filaments - may have
the appearance of brain-like convolutions
 Too large to pass readily through capillaries –extremely
large ones are seldom seen in blood smears, but are
found in body fluids other than blood.
 Remove from the circulating blood injured and dead cells
and cell fragments microorganisms, and insoluble
particles.
 Motile monophagocytes escaping between epithelial
lining cellos of the upper and lower respiratory tracts and
the gastrointestinal and genitourinary organs perform a
scavenger function, clearing the body of insoluble and
unneeded debris.
 Serve as first line of defense against microorganisms,
entrapping and killing these foreign invaders
B. Macrophages
 Derived from monocytes
 Circulating monocytes respond to inflammation and then
squeeze through the endothelium where they become
macrophages
 Main role is the removal of pathogens and necrotic
debris
 When a macrophage ingests a pathogen, the pathogen
becomes trapped in a food vacuole and fuses with a
lysosome.
 With the help of enzymes and toxic oxygen compounds
the pathogen is digested
 However, some bacteria such as mycobacterium
tuberculosis have become resistant to this method of
digestion
C. Polymorphonuclear (PMNs) leukocytes: active in inflammatory
process
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1. Basophil
have round, indented, band or lobulated nuclei
granules are dark
numbers increase during infection
leave the blood and accumulate at the site of the
infection or other inflammation
They then discharge the contents of the granules
(histamine, serotonin, prostaglandins and leukotrienes)
which increase the blood flow to the area and in other
ways add to the inflammatory process.
Play a part in hayfever and anaphylactic response to
insect stings
2. Eosinophil
 Characterized by relatively large, spherical granules
which have a particular affinity for the acid eosin stain.
 Usually have a band or two-lobed nucleus.
 Granules are spherical are uniform in size and usually
evenly distributed, fill the cell and rarely overlay the
nucleus
 In a good stain, the granules take a bright reddish-orange
stain with brownish tints.
 Gather wherever there is a parasite infection or allergic
reaction such as allergic asthma and then release their
toxins. The toxins are very efficient at harming parasites,
but will also harm us if released in the wrong place (
lining of lungs can become damaged in asthma )
3. Neutrophil
 Granules do not readily stain with either dye.
 Neutrophils (polymorphs), which can remove and kill
bacteria and particles of foreign material.
 The name 'neutrophil' ('neutro' = neutral, 'phil' = loving)
comes from the fact that they contain granules which are
neither acidic nor alkaline
 . The name 'polymorph' ('poly' = many, 'morph' = shape)
comes from the fact that like almost all cells in the body
they have a nucleus, but unlike other cells their nucleus
can have a variety of (many) shapes, consisting of usually
one to five connected lumps or 'lobes'.
D. Lymphocytes:
A. T-Cells
1. Cytotoxic T cells: (CD8+) destroy infected cells.
These cells function as “killer” or cytotoxic cells
because they are able to destroy target cells
which express specific antigens that they
recognize.
2. Helper T Cells (CD4+): are “middlemen” in the
immune response. When they get activated they
proliferate and secrete cytokines that regulate
effctor lymphocyte function. They are known as
the targets of HIV infection and the decrease of
CD4+ T cells results in AIDS. Some helper T cells
secrete cytokines that turn off the immune
response once an antigen has been eliminated
from the body
3. Regulatory T cells (suppressor T cells) suppress
activation of the immune system and maintain
immune system homeostasis. Failure of
regulatory T cells to function properly may result
in autoimmune diseases in which the
immunocytes attack healthy cells in the body.
CD = Clusters of Differentiation
Every effective immune response involves T cell activation; however, T cells
are especially important in cell-mediated immunity, which is the defense
against tumor cells and pathogenic organisms inside body cells. They are
also involved in rejection reactions.
B. B Cells
*Each B cell is programmed to make one specific antibody. For example,
one B cell will make an antibody that blocks a virus that causes the
common cold, while another produces antibody that zeros in on a
bacterium that causes pneumonia.
When a B cell encounters its triggering antigen(along with collaborating T
cells and accessory cells), it gives rise to many large plasma cells. Every
plasma cell is essentially a factory for producing antibody. Each of the
plasma cells descended from a given B cell (which are all members of the
same family, or clone) manufactures millions of identical antibody
molecules and pours them into the bloodstream.
A given antibody matches an antigen much as a key matches a lock. The fit
varies: sometimes it is very precise, while at other times it is little better
than that of a skeleton key. To some degree, however, the antibody
interlocks with the antigen and thereby marks it for destruction.