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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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