Immunology

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Immunology
Chapter 16, Lecture 2
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Richard L. Myers, Ph.D.
Department of Biology
Southwest Missouri State
Temple Hall 227
Telephone: 417-836-5307
Email: [email protected]
The Humoral Response
• Used for eliminating extracellular
pathogens
– produces many different antibody molecules
– each specific for a certain epitope
– may produce 1011 different antibodies
• In addition, the constant portion of the
antibody may account for biological
effector functions
• Humoral process requires participation of
other cells
– macrophages
– B cells
– also important is the interaction between TH and
antigen-class II MHC complex
• B cells are the principle cell in humoral
immunity
– they interact with antigen via a BCR
– proceeds with receptor-mediated endocytosis
• unlike macrophage which phagocytizes anything
– then antigen presented with a class II MHC on
the membrane
Humoral effector functions
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Activate complement system
Enhance phagocytosis via opsonins
Neutralize bacterial toxins
Neutralize viruses
Prevent colonization at mucosal surfaces
Involved in ADCC
Basic facts
• Immunocompetent B cells possess IgM and
IgD membrane bound antibodies
• Clonal proliferation and differentiation
occur after activation
• B cells have average cell cycle of 15 hr
• Unless activated by antigen, they will die in
a few days (usually 90% will die)
• Marrow produces about 107 B cells/day
General response to antigen
• The response is characterized by the
1) production of antibody-secreting cells
and 2) memory B cells
– during the lag phase cells undergo clonal
selection
– then the logarithmic phase occurs
• increase in antibody; it eventually declines
– for example, with SRBCs, lag phase lasts 4
days; peak plasma cell levels within 5 days;
peak antibody within 7 days
– IgM secreted initially, followed by IgG
• Referred to as the primary response
• Primary response with formation of
antibodies differs depending upon
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nature of the antigen
route of antigen administration
presence of adjuvants
species or strain
• Secondary response
different from primary
– response is more rapid
– produces more antibody
– lasts for a longer time
• maybe 1,000 times more
antibody produced
• Secondary response occurs
with second exposure to the
antigen
• Depends upon the existence
of memory B cells and
memory T cells
Plasma cell
Hemolytic plaque assay
• Assay to measure plasma
cell numbers in mice
primed with SRBCs
– many modifications
• Assay can be used to
quantitate plasma cells
secreting antibodies
specific for any antigen
• First, immunize mice with
SRBCs
• Prepare a spleen cell
suspension from a primed
mouse
• Mix in warm, melted agar to
which SRBCs have been
added
• Prepare a petri dish with a
layer of hard agar
• Overlay with mixture above
• Allow to cool and solidify
• Incubate for 1 hr at 37oC
• During incubation, antibodies
diffuse into agar and binds to
the SRBC
• Guinea pig serum containing
complement is added
• Complement reacts with the
bound antibody
– mediates lysis
• Lysis is indicated by a plasma
cell surrounded by a clear
plaque devoid of cells
• Plaques can be counted
– referred to as direct plaqueforming cells (PFC)
Elispot assay
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Plasma cells quantitated without SRBCs
Use antigen-primed splenocytes
Plate in agar containing antigen
Plasma cells secrete antibody which binds
to the antigen
• Remove cells
• Visualize bound antibody with ELISA
Associative (linked) recognition
• This is a process where
TH and B cells must see
peptides on the same
molecule for B cell
activation to occur
• In the following example
the epitope is a viral coat
(spike) protein
• T cells recognize internal
protein which allows B
cells to make antibody to
coat protein
• The activated TH cell
recognizes the processed
peptide together with the
class II MHC molecule
• Antibodies can then be
produced to the peptide
• Binding of antibody to
virus occurs
• There is also localized
release of cytokines
• Cytokines allow B cell to
proliferate/differentiate
• There are other membrane receptors
involved
– LFA-1 and CD4 are involved in cellular
adhesion
• Once in contact a signal generates the
expression of CD40L on the T cell
• This interacts with CD40 on the B cell
membrane
• This causes induction of cytokine receptors
• Results in fully activated B cells
– these can proliferate
Assignment
• Read Chapter 17,
Hypersensitivity
Reactions
• Review question 3
(pg 439)
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