The Immune System Overview. The specific immune system is mediated by leukocytes = white blood cells ( wbcs ). P hagocytosis : wbcs engulf invading organisms and destroy them Macrophages are large, long-lived phagocytic cells c ontaining many lysosomes.
The Immune System Overview
The specific immune system is mediated by leukocytes = white blood cells (wbcs)
Phagocytosis: wbcs engulf invading organisms and destroy them
Macrophages are large,
long-lived phagocytic cells
containing many lysosomes
Macrophages are found in the lymphatic system
Antimicrobial proteins attack microorganisms
The Inflammatory Response
Cell-Mediated response: Cytotoxic T cells
Both activated by Helper T cells
B and T cells are lymphocytes (specific type of leukocyte) made in the bone marrow
B cells mature in
the bone marrow.
T cells mature in
Antigen—a foreign substance that elicits a specific response by lymphocytes
produced by B cells
Antibodies and antigen receptors on the membranes of lymphocytes recognize and distinguish among antigens.
Epitopes—small, accessible portions of an antigen to which antibodies bind
Antibodies = Immunoglobulins (Igs): have 2 heavy
chains and 2 light chains joined by disulfide bridges
C regions = constant
V regions = variable (antigens bind to V regions)
Each lymphocyte will recognize and respond
to ONE and ONLY ONE antigen. Specificity is determined during development before any antigens are encountered.
When an antigen binds to the receptors, those specific lymphocytes are activated and
begin to divide.
Plasma cells secrete
antibodies. They are also called effectorcells.
producing clones of
cells that will destroy
a particular antigen
Memory cells: stick
around until the next
time the antigen appears
Primary vs. Secondary Immune Response
The immune system distinguishes self from nonself —> no lymphocytes are reactive against
the body’s own molecules.
An autoimmune disorder is when this system fails and the immune system destroys the body’s own tissues.
Class I MHC molecules present antigens to cytotoxicT cells.
Class II MHC molecules present antigens to helper T cells.
fight against pathogens
outside of cells
T cells fight against
pathogens that have already infected cells
B cells and macrophages are antigen-presenting cells (APCs). Class II MHC molecules present the antigens to helper T cells and bind to CD4on the helper T cell membrane. When bound to MHC II, the helper T cells proliferate. Helper T cells activate both the humor and the cell-mediated responses.
Cytokines (interleukins) signal other lymphocytes (B or T cells) to proliferate as well.
When cytotoxic T cells are activated, they kill infected cells.
CD8 (on the membrane of cytotoxic T cells) binds to class
I MHCs. When it recognizes a foreign antigen, it kills the
cell by releasing perforin.
Helper T cells and free floating antigens stimulate B cells to proliferate to make Ab-secreting plasma cells & memory cells. B cells present antigens on class II MHCs to make even more B cells!
Disposal of antigens by antibodies
Active immunity can be acquired naturally (after exposure to an antigen) or artificially (by a vaccine).
Vaccines are inactivated toxins that still have the epitopes available to trigger an immune response. Then if the antigen is actually encountered,
the immune response will be quicker (secondary response)
mom to baby
IgEsfor pollen bind to mast cell. When pollen binds, mast cell releases histamine triggers vessel dilation, increased permeability sneezing, etc.
Anaphylactic shock—acute allergic response when so many mast cells release histamine that there’s a dramatic drop in blood pressure. Epinephrine counteracts this response.
Immunodeficiency diseases—parts of the immune system fail to function properly.
AIDS is an immunodeficiency disease caused by the HIV virus. HIV infects cells that have surface CD4 receptors (helper T cells).
Fusin (CXCR-4)and CCR5
are coreceptors that help
the virus to enter cells.
Antibodies to the virus increase, and the virus levels drop initially. But its DNA is still present and replicating. And cells continue to be damaged.