Transcript 08 Human immune system

Human immune system
CELLS COOPERATION IN IMMUNE RESPONSE
PRIMARY OR CENTRAL LYMPHOID ORGANS
are responsible for synthesis and maturation of
immunocompetant cells.
These include the bone marrow and the thymus.
PERIPHERAL OR SECONDARY LYMPHOID ORGANS
are sites where the lymphocytes localise, recognise foreign antigen and
mount response against it.
These include the lymph nodes, spleen, tonsils, adenoids, appendix, and
clumps of lymphoid tissue in the small intestine known as Peyer's patches.
They trap and concentrate foreign substances, and they are the main sites
of production of antibodies.
Cells of the Immune System
White Blood Cells
Phagocytes - Neutrophils
Macrophages
Lymphocytes
White blood cells
Lymphocyte (could be B cell or T cell!)
Lymphocytes
• Present in lymphoid organs and in blood
• Groups
• T-lymphocytes (grow up in thymus)
• B-lymphocytes (grow up in bone marrow)
• Each one has receptors for a specific antigen
• Recognize millions of different antigens!
• Diversity generated by:
• rearrangement of antigen receptor genes
• different joining of the gene segments
• Gene rearrangement studies
Lymphocytes
B lymphocytes
• Live in blood, bone marrow, lymphoid tissues
• Basic function: make antibodies (immunoglobulins)
• B-cell receptor complex recognizes antigens
• binds antigen
• sends signals to T cells
• Antigens can be free and circulating (don’t have to be
bound to MHCs or displayed by other cells to be
recognized!)
The B-Cell Receptor
Lymphocytes
T lymphocytes
• Live in blood, bone marrow, lymphoid tissues
• Two basic functions:
• kill stuff
• help other cells do their jobs
• T-cell receptor (TCR) complex recognizes antigens
• binds antigen
• sends signals to the T cell
• Antigens must be:
• displayed by other cells…
• …AND bound to an MHC receptor
T Cell Selection in the Thymus
Chapter 21, Immune System
1821.7
Figure
The T-Cell Receptor
The T-Cell Receptor
Antigen-presenting cell
T cell
Lymphocytes
T lymphocytes
• Helper T cells
• CD4+ (and CD8-)
• help B cells make antibodies
• help macrophages eat bugs
• decreased in patients with AIDS
• Cytotoxic T cells
• CD8+ (and CD4-)
• kill virus-infected cells and tumor cells
CD8+ T cells surrounding tumor cell
Lymphocytes
Natural Killer Cells
• Belong to innate immunity arm
• No highly variable receptors like T and B cells
• Main job: recognize and kill damaged or infected cells
• Antigens don’t have to be bound to MHCs or displayed
by other cells!
Natural killer cell
Natural killer cell (top) killing infected cell (bottom)
Antigen-presenting cells
• Main job: catch antigens and display them to lymphocytes
• Dendritic cells
• Have fine cytoplasmic projections
• Present all over body: skin, lymph nodes, organs
• Capture bug antigens, display to B and T cells
• Other APCs
• Macrophages eat bugs and present antigens to T cells,
which tell macrophages to kill bugs
• B cells present antigens to helper T cells, which tell B cells
to make antibodies
dendritic cells
Antigen-presenting cells (APC) activate T helper cells
APC
presents
peptide
to Т helper
T helper 2 activates
B lymphocyte
Humoral immune response
Cell-mediated immune response
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