IB 202- Adaptive Immunity Activation

T-Cell Activation: Antigen Presentation

-dendritic cells collect info from environment and report to lymph nodes

-present antigens to T cells

-antigen presentation, key even linking innate and adaptive arms of immune system

3 Steps of T-Cell Activation

1) bacterium engulfed by phagocytosis into a dendritic cell

2) enzymes digest bacterium

3) epitopes (antigens) present on the cell surface

Immature T Cell and Antigen Presenting Cell Interaction

-Immature CD8+ T-Cell interact with class I MHC-bound antigens

• create mature cytotoxic T cell (Tc)

-Immature CD4+ T Cell interact with class II MHC-bound antigens

• create mature helper T cell (Th1/Th2)

-the cell carries the message to the T cell, if it’s foreign then mature T cells

Clonal Expansion of T cells

-activated T cells undergo clonal expansion to produce identical daughter cells

-T cells differentiate to become effector cells

• make helper and cytotoxic T cells

• helper T cells release cytokines

• cytotoxic T cells destroy pathogens

-some T cells become memory cells

Helper T Cells

-daughters of activated CD4+ T cells differentiate to effector helper T cells and activate other cells in immune response

What T cells help stimulate different cells in immune response?

1) TH1 stimulates cytotoxic T cells via cytokines

2) TH2 activates B cells

3) memory cells

Cytotoxic T cells

-daughters of activated CD8+ T cells are cytotoxic T cells:

• also called effector cells

• kill pathogens

• memory cells

4 Steps of B-cell Activation

1) BCRs on B cells interact with free-floating antigens in lymph/blood

• bound antigen internalized and digested into fragments then loaded to class II MHC proteins

2) TH2 helper cell w/complementary receptor arrives, binds to MHC-antigen complex on antigen-presenting B cell

• triggers activation signals to stimulate helper T cells

3) T2H helper cell releases cytokines that triggers clonal expansion of B cells

4) activated B cells replicate and some daughter cells differentiate into plasma cells

Inactive B Cell Morphology

-large nucleus, little cytoplasm, few mitochondria, ruffled plasma membrane

Activated B Cell Morphology

-produces large amounts of rough ER and mitochondria to manufacture and secrete antibodies

Difference between T cell and B cell activation?

• B cells interact with antigens directly

• only 1 type of B cell

• only 1 type of MHC on B cell

Different MHC and T Cells

-MHC 1 is protein presenting cell binding antigens to CD8 cells

-MHC II is protein on presenting cell binding to antigens on CD4 cells

Vitiligo and CD8 T cells

-mediated by CD8+ cells that destroy pigment-producing cells of epidermis, melanocytes

-cytotoxic T cell attack

HIV and CD4 T cells

HIV binds to CD4 molecules on surface of helper T-cells and replicates w/them

• destroys CD4+ T cells