Download IMMUNITY- humoral immunity, or antibody

Humoral Immunity
Human A&P II
Dr. Shaffer
Page 1
IMMUNITY- humoral immunity, or antibody-mediated immunity and cell mediated immunity
I. Antigens- substances that provoke an immune response
a. Complete antigens and haptens
i. complete antigens
1. immunogenicity- they stimulate proliferation of specific
lymphocytes and antibodies
2. reactivity- they react with activated lymphocytes and antibodies
3. almost anything can be a complete antigen, usually large, proteins
strongest
ii. Haptens- incomplete antigen
1. reactive
2. not immunogenic unless combined with protein carriers (example:
the lipids in poison ivy)
b. Antigenic determinants (AKA “epitopes”) - the immunogenic sites on the antigen
i. Most antigens have many different antigenic determinants
ii. Single antigen can mobilize many lymphocytes, stimulate production of
many antibodies
iii. Self-antigens- our cells would be antigens to someone else
1. MHC proteins (Major Histocompatibility Complex) on cell surface
2. MHC proteins bind to antigens in infected cells.
II. Cells of the Immune System: overview
a. Lymphocytes- all alike when released from red marrow. Develop
"immunocompetence" elsewhere.
i. T-cells mature (develop immunocompetence) in thymus
ii. B-cells mature in bone marrow
iii. Immunocompetent lymphocytes have unique receptors, committing them
to binding with a specific antigen
iv. Lymphocytes become immunocompetent before exposure to antigens
1. already programmed genetically
2. antigen exposure determines amount of proliferation of a given
type
3. some never get mobilized- no exposure to their particular antigen
v. After immunocompetency they go to lymphoid organs, they become "fully
functional" after binding with their antigens.
b. Macrophages- arise as monocytes in bone marrow
i. engulf foreign particles- present antigens on their surface
ii. secrete proteins that activate T-cells
iii. activated T-cells promote macrophages turning into insatiable "activated
macrophages"
III. Humoral Immune Response
a. Clonal selection and differentiation of B-cells
i. immunocompetent B-cell is activated when antigen binds to its surface
ii. B-cell grows and multiplies rapidly (all identical=clone)
a. Most of the cells become plasma cells cranking out
antibodies which bind to that antigen, marking it for
destruction
Humoral Immunity
Human A&P II
Dr. Shaffer
Page 2
b. some clone cells become memory cells ready to act fast if
exposed again.
b. Immunological Memory
i. "Primary Response"- has 3-6 day lag time, plasma antibody levels peak in
about 10 days
ii. Re-exposure leads to "secondary response" 2-3 days antibody blood levels
even higher than in Primary. Stay high for weeks to months
iii. This is similar to what happens to T-cells too.
c. Active and Passive humoral immunity
i. Active- antibodies produced after exposure to antigen
1. naturally
2. artificially
ii. Passive- antibodies come from serum of an immune individual (not always
human)
1. immediate protection
2. short lived protection
3. mother/ fetus
d. Antibodies- also known as "Ig"s (for immunoglobulins). Secreted by plasma cells
or by activated B-cells
i. Basic structure 1. "variable" region - antigen binding site
2. "constant" region - the stem) - determines the cells and chemicals
an antibody can bind to, and how that class of antibody will
function.
ii. Antibody classes. There are 5
1. classification is based on the C regions (constant regions)
2. different classifications have different roles. For example, some are
only found in secretions, some pass the placental barrier.
3. plasma cells can make more than one class of antibody with the
same antigen specificity.
iii. Antibody targets and functions. The antigen-antibody complex is the first
part of 4 different defense mechanisms.
1. neutralization - the antibody blocks sites on viruses or exotoxins
(bacterial toxins), then they can't bind to tissue cells and do them
harm.
2. complement fixation and activation - the main defense against
cellular antigens. After the antibody binds to the antigen, the C
region changes, exposing complement binding sites. This promotes
complement fixation and subsequent lysis of the cell.
3. antibodies can bind to more than one antigenic determinant. This
can have the effect of clumping together many foreign cells. This
agglutination is similar to precipitation, only precipitation is
when molecules (as opposed to cells) are clumped together. In both
agglutination and precipitation, the clumps are more easily
phagocytized.
Humoral Immunity
Human A&P II
Dr. Shaffer
Page 3
4. immobilization occurs when the antigenic determinant is
associated with cilia or flagella of the foreign organism. The
antibodies block the ability of the organism to move freely, again
setting them up for phagocytosis.