Introduction to the Immune
System
Adaku Ofoegbu, P3 Student
Pharmacy Biomedical Preview Program
adaku.ofoegbu@bison.howard.edu
Overview
General Introduction to Immune System
Types of immunity
Cells and organs
Antigens
Antibodies
Major Histocompatibility Complex (MHC)
Types of Immunity
• Innate Immunity
▫ This is your body’s first line of defense against
infection!
▫ This type of immunity is nonspecific
• Adaptive Immunity
▫ This immunity comes into play when an antigen is
introduced to the body
▫ This type of immunity is specific to the antigen
and is the basis for the “memory” of your immune
system
Examples of components of
innate immunity
• ANATOMIC
▫ Skin (dermis and epidermis)
and mucous membranes
• PHYSIOLOGIC
▫ Temperature
▫ Sebaceous gland secretions
(pH of 3 – 5)
▫ Chemicals (such as lysozyme
and interferon)
• PHAGOCYTIC
▫ Phagocytic white blood cells
(monocytes, macrophages,
etc) eat whole
microorganisms!
• INFLAMMATORY
▫ Inflammation leads to serum
proteins with antibacterial
activity going to site of tissue
damage or infection
Examples of adaptive
immunity
• Lymphocytes
• Antibodies
Humoral vs. Cell-Mediated Immunity
Humoral Immunity
Cell-mediated Immunity
• This immune response is
primarily seen in the blood
(hence “humoral”) and
involves macromolecules such
as:
▫ Antibodies
▫ Complement proteins
• Antibodies tag foreign bodies
(also known as antigens) so
that the immune cells can
destroy them
• Complement proteins basically
poke holes into bacterial cells
and cause them to lyse
• This immune involves cells
such as
▫ T-cells
▫ Phagocytes
• In this immune response, Tcells activate other immune
cells to enhance the immune
response
Lets talk about the cells first!
Cells of the Immune System
• Hematopoietic stem cells (HSC)*
• Lymphoid cells
▫ Natural killer cells (NK cells)
▫ B lymphocytes
▫ T lymphocytes
• Granulocytic cells
▫ basophils, neutrophils, eosinophils
• Dendritic cells
• Monocytes
Hematopoietic Stem Cells*
• These are the stem cells for ALL blood cells,
including red blood cells (RBCs) and white blood
cells (WBCs)
• These cells are located in the bone marrow
• (These are not actual immune cells but this is
where they originate)
Lymphoid Cells
• These cells circulate in the blood and lymph to
protect you from foreign pathogens in the body
• They make up 20-40% of your white blood cells
• The lymphoid cells include natural killer cells
(NK cells), B lymphocytes, and T lymphocytes
Lymphoid Cells
• Natural killer cells can recognize body cells
that are infected by viruses or are cancerous and
kill them without using antibodies!
Lymphoid Cells
• T lymphocytes (aka T cells) are comprised of
the helper T cells and the cytotoxic T cells
▫ Helper T cells have CD4 markers on them (hence
the CD4 count used in HIV patients)
▫ Cytotoxic T cells have the CD8 markers on them
• Special cells called antigen-presenting cells
present antigens to the T lymphocytes, which
will initiate a cascade immune response to the
antigen
Lymphoid Cells
• B lymphocytes (aka B cells) make up the
humoral immune response and make
antibodies
• They are are comprised of the effector cells and
memory cells
▫ Effector cells directly bind to free-floating antigen
in the body (T cells cannot do this)
▫ Memory cells
Granulocytic Cells
• The
granulocytic
cells are
essentially
white blood
cells that have
granules in
their cytoplasm
that can be seen
under a
microscope
Granulocytic Cells
• Neutrophils make up 50-70% of circulating
white blood cells and are phagocytes that tend to
eat bacteria
• Eosinophils make up 1 – 3% of circulating white
blood cells and tend to eat parasites
• Basophils make up <1% of circulating white
blood cells and are involved in some allergic
reactions
▫ Mast cells have a similar function as basophils and
are found in the tissues (as opposed to circulating
in the blood)
Dendritic Cells
• Dendritic cells are very potent antigenpresenting cells
• They are unique because they do not need to be
activated before they can present antigen to the
T cells
Monocytes
• Monocytes are a type of white blood cell that is
phagocytic
• They are among the largest in size of the white
blood cells
• They circulate in the blood, then enter the
tissues and become macrophages
Thymus
--site of T cell growth and maturation
Bone Marrow
--site of B cell growth and maturation
The Lymphatic System
--consists of the lymph nodes, spleen
Mucosal-associated lymphatic tissue (MALT)
--Peyer’s patches in small intestines,
What are antigens?
• Antigens are substances that can be recognized
by antibodies or by T-cells
• Antigens can cause immunogenic and/or
antigenic responses
▫ Immunogenicity – causing an immune response
▫ Antigenicity – the ability to combine with T-cell
receptors or antibodies
▫ A substance can be antigenic but not
immunogenic!
Facts about Antibodies
Antibodies are made by your B cells
Antibodies are comprised of 4 peptide chains
There are two heavy (H) chains and two light (L)
chains
IgG








IgA
LONGEST half life
Four forms of IgG
(IgG1, IgG2 , IgG3,
IgG4)
Activates
complement (in
order of best to
worst (3, 1, 2 ,4)
Fc region binds to
phagocytes (in
order, best to
worst (1 and 3, 2,
4)
Used for
SECONDARY
IMMUNE
RESPONSE
Participates in
precipitation
(form a lattice)
reactions with
immunogens and
opsonization
(complement
pathways)

γ2κ2
γ2λ2



IgM
Found in nasal

secretions

Forms LINEAR
polymers joined by Jchain







α2κ2
α2λ2


IgE
SHORTEST half life

PENTAMER (five
units attached when

floaing in blood)
Pentamer connected
via J-chain
BEST FOR BINDING
COMPLEMENT (the 
C1q)
NO CLASS
SWITCHING **MDs
don’t have class!**
Monomers present
on B cells (mature)
NO HINGE
PRIMARY IMMUNE
RESPONSE
Participates in
agglutination and
opsonization
µ2κ2
µ2λ2


IgD
Plays role in TYPE I
allergic response
Binds to mast cells
and basophils
helps cause
degranulation when
crosslinked
NO HINGE


Present on mature Bcells
NO CLASS
SWITCHING **MDs
don’t have class!**
Ɛ2κ2
Ɛ2λ2


δ2κ2
δ2λ2
**Antibody has four chains; two light chains – κ (60%) and λ (40%), and two dark chains (gamma, alpha, mu, epsilon, or
delta)
Major Histocompatibility Complex
• MHC is a type of molecule that exists on the
surface of your body’s cells
• There are two types of MHC:
▫ MHC I – found on virtually all body cells
▫ MHC II – found on the antigen presenting cells
• The CD4 on helper T cells looks at the MHC II
on the antigen presenting cells
• The CD8 on cytotoxic T cells looks at the MHC I
on your body cells
MHC I
• MHC I is present on virtually all body cells and
is how your immune system knows which cells
belong to itself!
• The cytotoxic T cells with CD8 look in the
peptide binding cleft for an unusual peptide
pattern (could be the result of a viral infection,
for example), and if the peptide is identified as
foreign, the cell is marked for destruction!