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Medical Microbiology
Chapter 11 – Elements of Host
Protective Responses
Our Defense Systems
 Our
body has 3 layers/walls of defense
against pathogens and toxins
• 1st = barriers
• 2nd = innate responses
• 3rd = antigen-specific immune
responses
 My Analogy
Barriers
 Barriers
• Skin
• Mucous membranes
• Secretions
– lactic acid and fatty acids (skin)
– mucus: filter for respiratory system, etc.
– Tears, lysozyme, stomach acid
• Normal flora
Innate Responses
Responses – they are always
present and ready to go.
• Complement Proteins
• Neutrophils and Macrophages
• Natural Killer cells
 Innate
Ag-specific Responses
 Must
be produced after infection
(usually takes 5-7 days)
• Activated B-cells produce
Antibodies
• Activated T-cells attack and destroy
infected cells and cancer cells
Players in Defense

Chemicals (allow communication between
cells):
• Cytokines – stimulate and regulate the
immune response
• Interferons – anti-viral proteins, stimulate
immune response
• Chemokines – involved with the
inflammatory response
– They lead to chemotaxis and activation
Players in Defense
 Table
11-1
 Cells (carry out the actual defense):
• Table 11-2 and Figure 11-1
• Some are designated by CD
“Clusters of Differentiation”
• MHC I – found on all nucleated cells
• MHC II – found on antigenpresenting cells (APCs)
Players in Defense
 Blood
cells of defense – Table 11-3
The Lymphatic System
 Functions:
• Return tissue fluid to the blood stream
– Why is this necessary?
– Example (~30L out of capillaries, 27L in)
• Fat transportation
• Immunity – defense against pathogens
and other foreign material
Lymphatic Vessels
 Lymph
capillaries – pick up interstitial
fluid
• lymph
vessels – have one-way valves
like the veins
 Lymph
• Lymph is dumped back into the blood
 Figures
from other text
Lymphatic Vessels
 As
the lymph travels back to the
blood stream it passes through
many lymph nodes
 Figures
Lymph Nodes
 Function
as filtering stations for the
lymph
 Macrophages are in the lymph
nodes
• What do they do?
 B-cells
and T-cells are also in the
lymph nodes
• Swollen lymph nodes
Lymph Nodules and Tonsils
 Lymph
nodules
• No lymph filtering
 Tonsils
are accumulations of lymph
nodules
• Function?
– swollen tonsils are a sign of a throat
infection
• Figure
Spleen
 The
spleen is the filtering site for the
blood
• Dead RBCs
• Figure