cell mediated immunity

what is an antigen?

a protein on the outside of a cell that acts as a marker

what is an antibody?

a protein produced by B cells that are complimentary to antigens and can attack pathogens

what are the structures of antigens like and where are they found?

Antigens are macromolecules found on cell membranes, bacterial walls, or viral surfaces

what is immunity?

the ability of an organism to resist disease

when are non-specific responses present from and do they give lasting immunity?

• present from birth

• don’t distinguish between pathogens

• do NOT give any lasting immunity

when are specific immune responses acquired and what do they result in?

• acquired during the organisms lifetime

• can distinguish between different pathogens

• result in an immunological memory that gives lasting protection to that specific pathogen

what happens as lymphocytes mature?

• they gain unique cell surface receptors

• these are specific and complementary to one type of antigen

what type of receptors do T cells and B cells have?

• T cells have T cell receptors

• B cells have antibody receptors

how do T lymphocytes respond to an organism’s own cells that have been changed in some way?

• virus infected cell

• mutated cells (early cancer cells)

• transplanted cells

• antigen presentation by macrophages

how do macrophages work?

• macrophage engulfs pathogens in phagocytosis

• Macrophage processes the antigens by combining them with glycoproteins in the cytoplasm called major histocompatibility complex (MHC)

• The MHC moves these pathogen antigens to the macrophage's cell surface membrane

• Macrophage is now an APC (antigen presenting cell)

how are T lymphocytes activated?

• T lymphocytes are activated when their particular cell receptor binds with the antigen on the body cells that have been changed

• (they only respond to antigens that are in the plasma membrane of a body cell)

what do T lymphocytes do after activated?

once activated (in clonal selection) they then go through:

• clonal expansion

• differentiation

what are the 3 steps for T lymphocytes when they encounter an antigen?

• clonal selection

• clonal expansion

• differentiation

what happens during clonal selection? (T cells)

• Specific T helper cell binds to the presented antigens (complimentary binding)

• The APC secretes interleukins (type of cytokine) to activate the selected T cells

what happens during clonal expansion? (T cells)

mass proliferation occurs:

• The selected T cells, stimulated by interleukins, divide rapidly by mitosis to form clones of identical T helper cells

• All the cloned activated T helper cells carry the same complementary receptor to a particular antigen

what happens during differentiation? (in T lymphocytes)

• interleukins (cytokines) promote the differentiation of cloned T cells

what are the 4 different types of T helper cells?

• helper T cells

• killer T cells

• regulatory T cells

• memory T cells

what do helper T cells do?

• release interleukins which stimulate B cells to divide and differentiate onto plasma cells

• assist other cells in the immune system (e.g. promote phagocytosis)

• activate Killer T cells

what do T killer cells (cytotoxic) do?

seek out and destroy infected cells or non-self cells

what do regulatory T cells (suppressor T cells) do?

• inhibit other cells in the immune system once pathogen has been eliminated

• act as a control and prevent autoimmune responses

what do memory T cells do?

remain in body for a long time and reactivate quickly during secondary response giving immunological memory

how do T killer cells work?

• active killer T cells attach to an antigen presenting cell, secrete perforins to lyse the cell membrane and release toxins such as H2O2 to destroy the cell

how is the immune response an example of cell signalling?

• Macrophages present antigens on their surface, signalling via proteins on cell surface

• Clonal selection - selection of the correct B and T lymphocytes through antigen receptor binding. Triggers release of interleukins leading to clonal expansion

• Clonal expansion - mitosis occurs and so numbers of lymphocytes increases

• T helper cells - release interleukins that stimulate B cells to develop and stimulate phagocytosis