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Topic 2: Cells of the
Immune System
Presented by Essence Perry
Immune System
● The immune system is the biological
structures and processes within an
organism that protects against
foreign substances by identifying and
killing pathogens and tumor cells.
● It detects a wide variety of agents,
from viruses to parasitic worms, and
needs to distinguish them from the
organism's own healthy cells and
tissues in order to function properly.
Cell Groups
Immune cells are divided into two
I. Lymphocytes: Derived in bone
marrow from lymphoid stem cells.
Help develop the ACQUIRED
immune system.
II.Granulocytes: Cells have large
granules in their cytoplasm. Help
develop the INNATE immune
Adaptive Immunity
● The humoral immune response occurs in the blood
and lymph, which were long ago called body
humors (fluids). In the humoral response,
antibodies help neutralize or eliminate bacteria,
bacterial toxins, viruses. and pathogens in the
blood and lymph.
● In the cell-mediated immune response, specialized
T cells destroy infected host cells. Defense against
cancer cells, virus-infected cells, fungi, animal
parasites, and foreign cells from transplants.
I. B cells
II. T cells
III.Natural Killer
I.B cell Progenitor (B cell)
Mature in bone marrow
Stored and mature in spleen
Involved for humoral immunity: response is
mediated by antibody molecules that are
secreted by plasma cells to prevent
intracellular infections
Once activated by antigen, proliferate into two
clones of cells: plasma cells that secrete
antibodies and memory cells that may be
converted into plasma cells at a later time
Perform antigen processing and presentation
Differentiate into two types of B cells:
○ Plasma cells
○ Memory B cells
B Cells continued…
Memory B Cells
● Remain “in reserve” so if
same pathogen appears,
the cells can immediately
differentiate into
cytotoxic and helper T
cells, causing a swift
secondary response to the
● Help gain immunity from
future infections
B Cells continued…
Plasma Cells
● A type of immune cell that makes
large amounts of a specific
● Plasma cells develop from B cells
that have been activated.
● A plasma cell is a type of white
blood cell. Also called plasmacyte.
II. T cell Progenitor
● Developed from stem cells in the
bone marrow
● Mature in the thymus
● Involved in cell-mediated
● Activated when another cell
presents antigen to them
● Several types of T cells (T cells
differentiate into… )
○ Cytotoxic T cells
○ Helper T cells
○ Suppressor T cells
T Cells continued…
Cytotoxic T Cells
● The term cytotoxic refers to their
use of toxic gene products to kill
infected cells.
● To become active, they require
signaling molecules from helper T
cells and interaction with a cell
that presents an antigen.
● Once activated, cytotoxic T cells
can eliminate cells that are
infected by viruses or other
T Cells continued…
Helper T Cells
● Cells triggers both the humoral and
cell-mediated immune responses.
● Helper T cells themselves do not
carry out those responses.
● Instead, signals from helper T cells
initiate production of antibodies
that neutralize pathogens and
activate T cells that kill infected
T Cells continued…
Suppressor T Cells
● Activated more slowly than
the other T cells
● Inhibit the response of the
immune cells to prevent
potential “autoimmune”
III. Natural Killer Cells
● Circulate through the body and
detect the abnormal surface
proteins of some virus-infected and
cancerous cells.
● Able to bind to certain tumor cells
and virus-infected cells without the
stimulation of antigens, and kill
them by the insertion of granules
containing perforin
● Inhibits the growth of cancer
I. Neutrophils
II. Eosinophils
IV.Mast Cell
V. Monocytes
A. Dendritic Cell
I. Neutrophils
● Circulate in the blood
● Are attracted by signals
from infected tissues and
then engulf and destroy
the infecting pathogens
II. Eosinophils
● Discharge destructive enzymes
● As soon as a parasite enters the
body, a chemical signal is sent out
that the eosinophils recognize and
tells them exactly where the
intruders are located
● Especially important in defense
against parasitic infections
III. Basophils
● Have large histamine-containing
granules that stain dark blue
● Release histamine (an
inflammatory chemical that
makes blood vessels leaky and
attracts other WBCs to the
inflamed site, and causes dilation
of the blood vessels)
● Aid in allergic and antigen
response by releasing the rarest
IV. Mast Cell
● Release histamine
● IgE antibodies bind to mast cells
and release histamine and other
inflammatory chemicals from
granules (vesicles)
● 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.
Dendritic Cells
● Important in alerting and activating
immune system cells to a threat such
as bacterial or viral invasion
● With their long, wispy extensions,
dendritic cells are very efficient
antigen catchers.
● Once they have engulfed antigens by
phagocytosis, they enter nearby organ
where they will present the antigens to
T cells.
● Most effective antigen presenters
known, it’s their only job.
Monocytes that have migrated out of
the bloodstream and into the body
tissues are macrophages
Engulf and destroy necrotic cell
debris and foreign material
including viruses, bacteria, and
tattoo ink
Extends long pseudopods to crawl
through tissue to reach infected site
Lysosomes within the cell digest the
infectious microorganisms it engulfs
Central actors in the final disposal
of cell debris as the inflammation
Are important in fighting chronic
infections, such as tuberculosis
Cytokines help develop the large