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Components of the Immune System
Learn on your own:
Spleen structure and function
Mast cells and NK cells
Self-Test Questions:
A1: all
A2: 1 - 4
A3: 1 - 3, 5
A4: 1, 2, 4
A5: all
A6: both
B1: none
B2: 1, 2, 4, 5
C1: all
C2: none
C3: all
D1: both
D2: 2 & 3
D3: none
Cells and Organs
1
“Hematopoiesis”
= Formation of blood cells
Stem cells
self-renewing
multipotent
(less differentiated)
progenitor cells
(more differentiated
vs blast cells
vs mature (naïve) cells
vs effector cells
Site of hematopoiesis
changes during development
Cells and Organs
2
Why is apoptosis (programmed cell death) also
Important?
-- a normal and essential process
Apoptosis vs
Necrosis (cell lysis)
Occurs during B- & T-cell
development
Also an important
killing mechanism
Prevents triggering of
inflammation Apoptosis
Cells and Organs
3
How can different cells be identified and separated?
Cells possess
different
CD antigens
With Immunofluorescence
CD antigens can be stained
with antibodies tagged
with fluorescent molecules
Flow cytometry and “fluorescence activated
cell sorting” (FACS) can be used to count,
sort and separate cell types
See appendix 5
Cells and Organs
4
What are the 2 major categories of immune cells?
1- Lymphoid cells
-- B- & T- cells
-- NK cells
2- Myeloid cells
-- Granulocytes
-- Monocytes, macrophages, DC
Lymphoid cells
B-cells -- naïve carry B-cell receptor (membrane Ab)
activated plasma cells secrete Ab
T-cells -- Carry T-cell receptor (TCR)
Tc cells are MHC-I restricted
activated become CTLs
TH cells are MHC-II restricted
activated secrete cytokines (TH1 vs TH2)
Cells and Organs
5
Myeloid cells
A. Granulocytes
-- degranulation
Neutrophils
-- multilobed
-- rapid response
Eosinophils
-- bilobed
-- eukaryotic parasites
Basophils
-- densely granular
-- eukaryotic parasites
-- type I hypersensitivities
Neutrophil chase
Cells and Organs
6
Granulocyte abnormalities can
underlie disorders
Eosinophilia
-- too many eosinophils
Causes
Allergies
Parasitic infections
Neutropenia
-- too few neutrophils
Causes
Leukemia
Congenital
Drug-induced
Cells and Organs
7
B. Other myeloid cells
Macrophages
Develop from monocytes (in blood)
-- within tissues
Go by various names; e.g.:
-- Kumpfer cells, Langerhans cells, microglial cells, etc
-- tissue type specific
How do macrophages kill pathogens?
-- external & internal mechanisms
-- enzymes and reactive molecules
Act as “Professional-APCs”
-- only to memory T-cells
Cells and Organs
8
Dendritic Cells
Functions: antigen…
Capture
Processing
Presentation
Antigen + T-cell interaction…
 “licensed DC”

Only licensed DC can
activate naïve T-cells
Take on specialized functions
-- determined by cytokines
-- generate different types of T-cells
Cells and Organs
9
What are the organs of the
immune system?
Primary lymphoid organs
(naïve immune cell development)
Bone marrow
Thymus
The “Nude Mouse”
Secondary lymphoid organs
(immune cell activation)
Cells and Organs
10
Structure and function of
2O lymphoid tissues
“Follicle”
-- basic organizational unit
-- may be within specialized organ
2O tissues carry out
surveillance of systems
-- respiratory : tonsils & MALT
-- digestive : GALT
-- circulatory : spleen
-- lymphatic : lymph nodes
-- skin : SALT
What happens in these tissues
AG presentation
cell : cell interactions
cell activation
Cells and Organs
11
Immune Surveillance
Circulation of cells
and Interstitial fluid
-- antigens / pathogens
-- immune cells
Cell extravasation
-- Chemokines
-- post-venous capillaries
-- receptors
-- adhesion proteins
Leukocyte Rolling
Cells and Organs
Leukocyte Homing
12
Structure and function
of lymph nodes
Lymphatic vessels
afferent
efferent
Cortex
Follicles & Germinal centers
1O vs 2O
B-cell activation
Paracortex
AG-presentation &
T-Cell activation
Medulla
Plasma cell
accumulation
Cells and Organs
13
Mucosal-Associated
Lymphoid Tissue (MALT)
Widely distributed
-- More about MALT in Chapter 12
e.g., Peyer’s patches (GALT)
-- Protects Intestinal track
-- M-cells
Cells and Organs
14
Recent findings show effect of HIV on GALT
Destruction of T-cells in gut
Leads to destruction of GALT
Ileum of:
Uninfectected person
HIV infected person
GALT
Image by Daniel Douek from Science (2005) 307: 1395
Cells and Organs
15