Mature (naive) B cells

1. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation Plasma cells produce antibody; depending on site of infection and duration of exposure, the class may be IgM, IgG, IgA, or IgE Memory cells Th 1 cells activate macrophages that present antigen via MHC class II molecules; also produce cytokines that orchestrate other responses Effector T-cytotoxic cells destroy cells that presented antigen via MHC class I molecules; also produce cytokines that allow neighboring cells to become more vigilant against intracellular pathogen.

2. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells

3. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs

4. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Dendritic cells gather antigen

5. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Dendritic cells gather antigen

6. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Naive T-cytotoxic (CD8) cells Dendritic cells gather antigen

7. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Naive T-cytotoxic (CD8) cells Dendritic cells gather antigen Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells

8. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Naive T-cytotoxic (CD8) cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells

9. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells

10. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Th2 Th1

11. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Th2 Th1 Free antigen

12. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Th2 Th1 T-dependent antigens Free antigen Naive B cells

13. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation

14. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation Memory cells

15. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation Plasma cells produce antibody; depending on site of infection and duration of exposure, the class may be IgM, IgG, IgA, or IgE Memory cells

16. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation Plasma cells produce antibody; depending on site of infection and duration of exposure, the class may be IgM, IgG, IgA, or IgE Memory cells Th 1 cells activate macrophages that present antigen via MHC class II molecules; also produce cytokines that orchestrate other responses

17. Primary lymphoid organ (bone marrow) Immature B cells Primary lymphoid organ (thymus) Immature T cells Mature (naive) B cells Mature (naive) T cells Tissues Secondary lymphoid organs Travel to secondary lymphoid tissue, developing into antigen- presenting cells; co-stimulatory molecules are expressed if antigen represents microbial invasion or tissue damage. Antigen presented by MHC Class I molecules in the presence of co-stimulatory molecules activates naive T-cytotoxic cells. Activation, proliferation, development of effector T cell functions Memory T-cytotoxic cells Naive T-cytotoxic (CD8) cells Effector T-cytotoxic cells Dendritic cells gather antigen Activation, proliferation, development of effector T cell functions Memory T-helper cells Naive T-helper (CD4) cells Antigen presented by MHC Class II molecules in the presence of co-stimulatory molecules activates naive T-helper cells Effector T-helper cells Activates B cells that present antigen Th2 Th1 T-dependent antigens Free antigen Naive B cells Activation, proliferation, class switching, affinity maturation Plasma cells produce antibody; depending on site of infection and duration of exposure, the class may be IgM, IgG, IgA, or IgE Memory cells Th 1 cells activate macrophages that present antigen via MHC class II molecules; also produce cytokines that orchestrate other responses Effector T-cytotoxic cells destroy cells that presented antigen via MHC class I molecules; also produce cytokines that allow neighboring cells to become more vigilant against intracellular pathogen.