Cell Mediated Immunity

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Cell mediated immunity

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Direct attack on pathogens which hide inside our cells (tuberculosis bacteria, viruses) by T lymphocytes, which secrete cytokines (interleukins)

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1. Cytotoxic T cells

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function to directly destroy pathogens (CD8+)

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2. Helper T cells

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aid in immune response via secretion of interleukins (CD4+)

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3.Suppressor (regular) T cells

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secrete interleukins that limit the immune response
CD= cell differentiation; refers to surface glycoproteins; refers to surface glycoproteins

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Activation of T lymphocytes

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T cells can't "see" antigen unless its processed into fragments and presented to them. This requires accessory cells called antigen presenting cells (APCs)
1. Macrophages
2. B-lymphocytes
3. Dendritic cells
All of these express MHC Class II

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Cytotoxic T lymphocytes bind to, and destroy?

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"self" cells which express MHC Class I AND display abnormal proteins (often due to viral infection or cancer)

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Helper T cells express?

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CD4 proteins that bind to MHCII

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CD4 protein & antigen receptor recognize ?

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the MHCII glycoprotein complexed with a foreign antigen

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Activation is via ?

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macrophages, dendritic cells and B cells

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Requires co-stimulation with ?

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interleukins (1,2) and other co-stimulatory signals from APCs

This requirement for 2 signals for activation is a safeguard to prevent the immune system from destroying healthy cells

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Activated Helper T lymphocytes secrete interleukins

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-Stimulate B cell proliferation (interleukin 4 & other cytokines) Note: these chemical signals are necessary for full B cell activation
-Stimulate cytotoxic T cell proliferation
-Stimulate Natural Killer (NK) cells
-Stimulate macrophages to become potent killers

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Cytotoxic T lymphocytes express CD8 proteins that bind to MHCI

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-Activated by cancer cells or infected cells (bacteria, viruses)
-Proliferation is stimulated by Helper T cells
-Kills foreign cells via chemical agents:perforins, granzymes
-Killing requires binding of cytotoxic T lymphocyte to the cell

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Congenital (immunodeficiencies)

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Ex: children are born without B and/or T cells

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Acquired (immunodef)

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Ex: HIV infection which can progress to AIDS (acquired immunodeficiency syndrome) if not treated.

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Human immunodeficiency virus (HIV) was first identified?

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in 1981

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Virus (AIDS) is transmitted through which body secretions?

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blood, sexual & birth fluids, saliva, and tears

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HIV enter its target tissue (helper T cells) via?

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CD4 proteins

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No symptoms during the replication phase as HIV is spreading through the?

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Lymphatic system, but the loss of T cells (and others) eventually depresses cell-mediated immunity.

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What happens once the virus is no longer contained in lymph nodes?

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immune system collapses. Death occurs due to opportunistic infections, tumors, or both