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Objectives
After working through this module, you should be
able to:
Describe in general the phases of immune response.
Explain the mechanisms involved in humoral
immunity.
Explain primary and secondary antibody responsestoward antigen.
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Immune Response
Phases of Immune Response
- Antigen recognition
- Lymphocyte activation
- Antigen elimination
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Lymphocyte Activation
T and B cells undergo proliferation and clonal
expansion T helper (TH1, TH2), T cytotoxic (TC),
T suppressor (TS), T memory, antibody
producing B cells (plasma cells), B memory
TH cells develop into effector cells that function by
secreting cytokines
Different cytokines act on B cells, T cells andmacrophages
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Lymphocyte Activation
MacrophageNK cell
TH2TH1
IFN-
IL-12IFN-
Il-12, TNF-
IFN-
Il-4, IL-10
Cross-regulation
Promotes cellular immunity Promotes humoral immunity
IL-4
IL-5IL-6
IL-10
IL-13
IL-2
IFN-TNF-
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ACTIVATION OF B-LYMPHOCYTE
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B cell uses surface Ig (sIg) to recognize antigen which isinternalized and presented to T cell as peptide-MHCclass II complex - T-dependent antigen
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Lipopolysaccharide activates irrespective of sIg
(T-independent antigen)
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Repeating antigen (e.g. complex sugars) cross-links
sIg and activates B cell - (T-independent antigen)
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A ti Eli i ti
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Antigen Elimination
The elimination ofantigens in the effector phase ofspecific immune responses occurs by the
cooperative actions of differentiated lymphocytes
and defense mechanisms of innate immunity
ACTIVITY 1
How does antibody eliminate antigen in thehumoral immune response?
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Primary humoral response:
The activation and response of lymphocytes specificfor a newly encountered antigen; generally slower and
weaker than the secondary immune response.Secondary humoral response
secondary immune response occurs after a second orsubsequent exposure, develops much more rapidly,
and is mediated primarily by immunoglobulin G (IgG)
Primary Response: Secondary Response
Slow in Onset Rapid in Onset
Low in Magnitude High inMagnitude
Short Lived Long Lived
IgM IgG (Or IgA, or IgE)14
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Differences between Primary and SecondaryImmune Response
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Primary humoral response Secondary humoral response
Responding B cell
Lag period
following antigen
administration
Time of peak
response
Magnitude of
peak antibody
Isotype produced
Antigens
Antibody affinity
Naive (virgin) B cell
Generally 47 days
710 days
Varies depending on antigen
IgM predominates early in theresponse
Thymus-dependent and thymus-
Independent
Lower
Memory B cell
Generally 13 days
35 days
Generally 1001000 times higher
response than primary response
IgG predominates
Thymus-dependent
Higher
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