MBL5 - Cell mediated Immunity

What is the superantigen?

A class of antigens that bind directly to MHC molecules without processing.

Describe briefly the T-cell receptor (TCR).

A molecule found on the surface of T lymphocytes that is responsible for recognizing fragments of antigen as peptides bound to MHC molecules. +T cell receptor associated with CD3 a signaling complex make up the TCR complex.

Cell mediated immune responses are regulated by MHC. What is the major histocompatibility complex (MHC)?

A set of specialized proteins expressed on surface of host cells. * In humans - HLA, large genetic locus present on Chromosome 6.

Explain briefly the exogenous antigen processing pathway.

Presentation on the cell surface together with class II MHC to CD4+ T lymphocytes.

State the clinically important superantigens & the clinical features.

Staphylococcal enterotoxins. Cause food poisoning & toxic shock syndrome toxin

State 2 classes of MHC molecules & their location respectively.

1. MHC Class I - present on most nucleated cells. 2. MHC Class II - present on dendritic cells, macrophages & B cells.

Explain briefly the endogenous antigen processing pathway.

Presentation on the cell surface together with class I MHC to CD8+ T lymphocytes. + Endogenous antigens - autoantigens, foreign antigens from viral, intracellular parasites or tumorous antigens.

T cell-mediated immune response begins in the secondary lymphoid organs. True or False.

True. The T cell-mediated immune response begins in the secondary lymphoid organs: spleen, lymph nodes, and organized lymphoid tissues associated with mucosal surfaces including Peyer's patches, tonsils and gut-associated lymphoid tissues.

State 3 functions of cytokines produced by CD4+ T helper cells.

1) Can be directly toxic to the target cells. 2) Can stimulate other T cell effector functions & B cell antibodies production. 3) Can mobilize powerful inflammatory mechanisms.

Activated T cells rapidly proliferate (clonal expansion) & perform effector functions. State 2 effector functions of activated T cells.

1) Cell-mediated cytotoxicity by CD8 T cells. 2) Production of various cytokines by CD4 T cells.

State 3 major roles of cell-mediated immunity.

1) Defense against viral & other intracellular pathogens. 2) Delayed type hypersensitivity (DTH). 3) Graft rejection.

Name 3 substances secreted by Cytotoxic T cells that leads to apoptosis.

1) Granulysin. 2) Granzymes. 3) Perforins.

Superantigens are capable of activating up to 20% of the body's T-cells. State the results of superantigens response.

1) Massive production of CD4 T cell cytokines. 2) Systemic cytotoxicity. 3) Suppression of adaptive immunity.

List 5 antigen presenting cells (APCs) & their location respectively.

1) Monocytes - peripheral blood. 2) Macrophages - tissues. 3) Dendritic cells - lymphoid tissues. 4) Langerhans cells - epidermis. 5) B lymphocytes.

State 2 key functions of MHC molecules.

1) Selectively bind to peptides produced when proteins are produced inside host cells. 2) Present peptides on surface of host cell to a T cell. * They allow T cells to distinguish self from non-self.

Name 3 examples of cell-mediated immune response.

1) Tuberculin test (DTH). 2) Contact sensitivity. 3) Graft rejection.

Explain briefly the role of Helper T cells in macrophage activation.

1. Macrophages routinely engulf invading microbes resistant to lysosomal killing. 2. TH cells recognize macrophage with engulfed microbes resistant to killing. 3. TH cells activate macrophages by delivering cytokines that induce more potent destructive mechanisms.

State how naïve T cell is activated in CMI.

Antigenic peptides are presented to naïve T cells in secondary lymphoid organs by APC. Resulting in activation of naïve T lymphocytes

Grafts of a kidney, heart, lung, liver, etc. from one human to another always (unless donated by an identical twin) are seen by the recipient's immune system as antigenic and elicit an immune response. If unchecked, this response will eventually lead to destruction of the graft. Name the T cells responsible for this CMI response.

Both CD4+ and CD8+ T cells participate in graft rejection.

State the T cells responsible for Tuberculin test (DTH).

CD4+ T Cells

Many people develop rashes on their skin following contact with certain chemicals such as nickel, certain dyes, and the active ingredient of the poison ivy plant (contact sensitivity). Name the T cells responsible for this CMI response.

CD4+ T cells.

Each type of T lymphocytes responds to different types of antigens, activated by different antigen presentation, and has different effector function. Justify this statement.

CD4+ T helper cells: 1. Responds to exogenous antigens. 2. Activated by class II MHC. 3. Effector function is cytokine production. CD8+ T cytotoxic cells: 1. Responds to endogenous antigens. 2. Activated by class I MHC. 3. Effector function is cell death.

What is the naïve T cells?

T cells that have not yet encountered foreign antigen & have not yet been activated.

Name the type of lymphocytes responsible for the cell mediated immunity.

T lymphocytes. 1. Recognize foreign antigens on the surface of cells, organisms, or tissues. 2. Regulate proliferation and activity of other cells of the immune system: B cells, macrophages, neutrophils.