Chapter 16, Lecture 2
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
– 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
– 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
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
– 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
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
• 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
• Prepare a spleen cell
suspension from a primed
• Mix in warm, melted agar to
which SRBCs have been
• 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
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
• There are other membrane receptors
– LFA-1 and CD4 are involved in cellular
• Once in contact a signal generates the
expression of CD40L on the T cell
• This interacts with CD40 on the B cell
• This causes induction of cytokine receptors
• Results in fully activated B cells
– these can proliferate
• Read Chapter 17,
• Review question 3
(pg 439)
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