Micro - Ch 15 - Adaptive Immunity

frederick loeffler

found club-shaped bacteria

Emil von Behring

injected diphtheria toxin into guinea pigs that had recovered from diphtheria

• suggested something in blood protected - antitoxin

True or False: adaptive immunity has memory

true

primary response 

first response to an antigen 

secondary response

the adaptive immune system remembers the mechanism that proved effective against the specific antigen 

• if encountered again, a stronger secondary response results 

humoral immunity 

works to eliminate extracellular antigens 

• bacteria, toxins, viruses in bloodstream

cell-mediated immunity

deals with antigens residing within a host cell

B cells

develop in bone marrow

differentiate into plasma cells in response to extracellular antigens 

• produce Y shaped proteins called antibodies 

• bind to antigen with high degree of specificity 

• some B cells form memory B cells - respond quickly if antigen is encountered again 

how do antibodies protect directly

by binding to antigen, preventing attachment to cell

how do antibodies protect indirectly

by tagging antigen for elimination

B cell receptor

membrane bound version of a B cells specific antibody - binding antigen triggers response

• usually need confirmation from helper T cell 

T cells

mature in thymus

helper T cells and cytotoxic T cells help to eliminate antigens 

3rd subset is regulatory T cells 

Helper T cells & Cytotoxic T cells

must be activated before they can multiply

dendritic cells are responsible for T cell activation

antigen

molecule that reacts specifically with an antibody

immunogen

antigen that elicits an immune response

antigenic / immunogenic used interchangeably - ability of an antigen to elicit an immune response

two parts of an antibody

two identical arms (Fab region)

stem (Fc region)

variable region

at ends of Fab regions, accounts for specificity

constant region

includes Fc and part of two Fab regions

what type of bonds hold the antibody together

disulfide

five classes of immunoglobulins

IgM, IgG, IgA, IgD, IgE

• each class has different constant region of heavy chain

• each class had distinct functions and properties

IgM

first class produced during a primary response 

pentamer 

• 5 monomeric subunits, gives antibody 10 antigen-binding sites

cannot cross from bloodstream to tissues

• primary role in bloodstream infections

most efficient class in triggering classical pathway of complement system

5-13% of circulating antibodies

IgG

80-85% of total serum immunoglobulin

generally first and most abundant circulating class produced during secondary response 

protect via neutralization, aggregation, opsonization, complement activation, and antibody dependent cellular cytotoxicity  

can cross placenta to fetus’s bloodstream 

IgG found in colostrum, absorbed by newborns intestinal tract 

IgA

10-13% of serum antibodies

is a dimer 

secreted form is important in mucosal immunity 

IgD

less than 1% of serum immunoglobulin 

involved with development and maturation of antibody response

• function in blood not clearly defined 

• on the surface of B cells  

IgE

barely detectable in normal blood

cause allergic reaction

tightly bound via Fc region to basophils and mast cells 

antigen binds to antibody carried by mast cell - cell releases histamine - causes inflammatory response 
basophils and mast cells can also release chemicals when IgE binds to allergens

• some allergic reactions can be life threatening