CH. 15- "Host defenses II"

acquired (specific) immunity

refers to antigen specific immune response; can only be achieved after immunizing event such as infection

Products of B and T lymphocytes

undergo a selective process to specifically respond to only one antigen

Immunocompetence

the ability of the body to react with countless foreign substances

Specificity

highly specific to the antigen against which the third line of defense is directed

memory

the rapid mobilization of lymphocytes that have been programmed to recall their first engagement with the invader and rush to the attack again

B cells are formed in

bone marrow

T cells are formed in

thymus

plasma cells secrete

antibodies

MHC molecules

indicate self

Class 1 MHC

-appears on all nucleated cells
-displays unique characteristics of self
-each human inherits a particular combination of class I MHC genes.

Class II MHC genes:

-codes for immune regulatory markers found on macrophages, dendritic cells, and B cells.
-involved in presenting antigens to T cells during cooperative immune reactions.

Cluster of Differentiation (CD)

-Markers important in immunity
-Found on the membranes of a variety of different cells involved in the immune response
-Over 300 have been described

Tissue dendritic cells

-Ingest the antigen
-Migrate to the nearest lymphoid organ
-Process and present antigen to T-lymphocytes

antigen presenting cells

dendritic cells, macrophages, B cells

B cells and T cells proliferate and differentiate when

they are challenged by antigen

clone

-proliferation of a particular lymphocyte.
-genetically identical cells, some of which are memory cells.

Helper T cells

activate macrophages, assist B-cell processes, and help activate cytotoxic T cells

Regulatory T cells

control the T-cell response

Cytotoxic T cells

A type of lymphocyte that kills infected body cells and cancer cells

when activated by an antigen, B cells

divide and give rise to plasma cells

Plasma cell function

produce antibodies

markers are found on all cells except

Reb blood cells

stem cells become granulocytes, monocytes, or lymphocytes in the

bone marrow

Lymphocytes

can either become B or T cells

B and T cells are each equipped to

respond to a single unique antigen

immunoglobulins

bind with specific antigens in the antigen-antibody response

immunoglobulins are composed of

-two heavy (H) chains
-two light (L) chains
-one light chain is bonded to one heavy chain
-the two heavy chains are bonded to each other with disulfide bonds
-creates a symmetrical Y-shaped arrangement

antigen binding site

pockets on an antibody
that bind specific antigens

variable regions

-found in antigen binding sites
-amino acid position is highly varied from one clone of B lymphocytes to another as the result of genetic reassortment

constant regions

amino content does not vary greatly from one antibody to another

T cell receptor

similar to be cell receptor; different because it is small and never secreted

clonal selection theory

States that the antigen selects which lymphocyte will undergo clonal expansion and produce more lymphocytes bearing the same type of receptor.

immune tolerance

-removal of any potentially harmful clones through clonal deletion
-autoimmune diseases arise from loss of immune tolerance

the B-cell receptor is

immunoglobulin

T cell display CD3 marker and either the

CD4 or CD8 coreceptor

Antigen

A protein that, when introduced in the blood, triggers an immune response in specific lymphocytes

Immunogenicity

Ability of pathogens to induce an immune response

epitope

Small, accessible portion of an antigen that can be recognized.

Haptens

antigens too small to provoke immune responses; attach to carrier molecules and can develop immunogenicity.

molecules with molecular weight between 1000-10,000 are

weak antigens

molecules with molecular weight of

100,000 are most immunogenic

Alloantigens

cell surface markers and molecules that occur in some members of the same species but not in others; responsible for incompatibilities that occur in blood transfusions or organ grafting

three molecules that serve as antigens

-lipoproteins
-glycoproteins
-polysaccharides

role of antigen processing and presentation

-in order for the T cells to recognize antigens, an antigen must be further acted upon and formally presented to lymphocytes by cells called antigen-presenting cells (APC's)