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Chapter 6 – EffectorMechanisms of T Cell–

Mediated Immunity

Dr. Hafez Sumairi

Learning outcomes

1.How do effector T lymphocytes locateintracellular microbes at any site in the body?

2.How do effector T cells eradicate infections bythese microbes?

3.What are the roles of macrophages and otherleukocytes in the destruction of infectiouspathogens?

Types of T cell–mediated immunereactions• CD4+ helper T cells secrete

cytokines that recruit andactivate other leukocytes tophagocytose (ingest) anddestroy microbes.

• CD8+ cytotoxic Tlymphocytes (CTLs) killany infected cell containingmicrobial proteins in thecytosol or nucleus,eliminating cellularreservoirs of infection

Migration of Tlymphocytes in cell-mediated immunereactions

Migration of Tlymphocytes in cell-mediated immunereactionsThe migration of naiveand effector T cells arecontrolled by threefamilies of proteins—selectins, integrins, andchemokines

Effector functions ofCD4+ helper TlymphocytesCD4+ T lymphocytes of the

• TH1 subset enhance the ability ofphagocytes to kill microbes

• TH17 cells promote the recruitment ofleukocytes to the site of infection

• TH2 cells activate eosinophils to killhelminthic parasites

Bidirectionalinteractions• Effector T lymphocytes of

the TH1 subsetthat recognize macrophage-associated antigens activatethe macrophages by CD40ligand–CD40 interactionsand by secreting thecytokine interferon-γ (IFN-γ)

• Delayed typehypersensitivity (DTH)

Role of TH2 cells inhost defense• The TH2 subset of CD4+ T

lymphocytes stimulateseosinophil-richinflammation, which isimportant in defense againsthelminthic parasites.

• TH2 cells secrete cytokinesthat inhibit classicalmacrophage activation andstimulate the alternativepathway of macrophageactivation

Effector functions ofCD8+ cytotoxic Tlymphocytes

Cooperation betweenCD4+ and CD8+ T cellsin eradication ofintracellular infections

• Resistance ofpathogenic microbesto cell-mediatedimmunity

• Different microbes have developeddiverse mechanisms to resist Tlymphocyte– mediated host defense

Thank you