acquired immunity: B cells and immunoglobulins

antigen

a foreign molecule that is recognized by the immune system to elicit a protective response

epitope

Region of the antigen that is specifically recognized

haptin

an incomplete antigen that cannot mount an immune response on

its own, needs a carrier (otherwise it is too small!!)

what can be an antigen 

proteins

polysaccharides

proteins

Bacterial toxins and enzymes

Fungal cell toxins and enzymes

polysaccharides 

Bacterial cell walls

Fungal cell walls

Capsules

specific modifications on proteins

Addition of sugar groups onto proteins

• different blood groups 

lipids are usually

poor antigens

what can lipids be if not antigens

recognized

PAMP

Pathogen Associated Molecular Pattern 

PAMP components

LPS – gram (-) bacteria

Flagellin

Peptidoglycan

Double stranded RNA

PAMP is a

sign of infection

DAMP is a

sign of tissue damage

DAMP

Danger Associated Molecular Pattern

DAMP conpoenents

• Heat Shock Proteins

• Hyaluronic acid fragments

• ATP

what can be recognized b y toll-like receptors

PAMP and DAMP

what are PAMP and DAMP

non-specific

what do B cells provide

humoral immunity with antibodies

types of T- cells

cytotoxic and helper

Cells of the adaptive immune system

B and T cells

what are antibodies produced by

plasma cells

what do antibodies do

Recognize epitope and adhere to the surface.

what do antibodies act as

a molecular marker for innate immune system

what do antibodies consist of

light- and heavy chain subunits each with a constant and variable domain

what is a B-cell receptor

like an antibody but attached to the surface of a B cell

IgM antibodies functions

primary response antibody (first made),activates complement (very strong), monomer serves as B- Cell receptor

IgG antibodies functions

• Secondary response and memory

• Activates complement

• Can cross placenta

• Interacts with phagocytes to trigger opsonization

IgA antibodies functions

• Secretory antibody (saliva, milk, mucous)

• Associated with mucosal immunity

• Inactivation of pathogens

IgE antibodies functions

• Stimulates allergy responses

• Bound tightly to mast cell surface

• Causes degranulation and release of histamine

IgD antibodies functions

B cell receptor (found on surface of B cells)

antibodies active b cells through

b cell receptors

what do antibodies lead to

opsonization

• help the innate immune system destroy pathogens 

what do antibodies do to toxins and bacteria

Clumping and inactivation oftoxins and bacteria

what do antibodies activate

• other cellular defense mechanism (antibody dependent cellular cytotoxicity and Mast Cell degranulation)

• complement system 

Antibodies have two major functional parts…

Fab and Fc

Fab

recognizes and binds to epitope on antigen

Fc

is recognized and bound by receptors on cell surfaces

Antibodies bound to pathogens are

recognized by phagocytes and brought into the cell and destroyed

what do antibodies act as

an enhancer to phagocytosis and clearing of pathogens

Antibody-dependent cell mediated cytotoxicity

Antibodies bound to cell are recognized by NK (natural killer) cells

NK cells release perforins and granzymes (enzymes that act to kill the foreign cell)

what does Antibody-dependent cell mediated cytotoxicity require 

antibody:antibody receptor recognition

what do B- cells receptors have

a transmembrane domain

what do B cell receptors do when bound to epitope

starts a signaling cascade that activates the B cel

what is important to B cell development 

B-cell receptors

what are immunoglobulin genes

multi-gene family found on different chromosomes

what is Immunoglobulin diversity the result of

genetic recombination events

what does genetic recombination allow

our immune system to generate immunoglobulins that can bind to nearly any antigen

what are the 2 steps required for B cell activation:

1. Antigen interacting with the B cell receptor

2. Helper T cell interaction with B cell by releasing stimulatory cytokines

cytokines

small proteins that can alter how a cell behaves

• think of them as communication signals between cells 

what does Major histocompatability complex II act as

a glove

what does the Major histocompatability complex II do 

presents antigen to other cells within the immune system

what is the Major histocompatability complex II loaded with

antigens obtained from extracellular spaces

what does Major histocompatability complex II interact with

T cells for second step of B cell activation

Processing of antigen by B cell

1)The bound B cell receptor is brought into cell along with antigen

2)The proteins are destroyed and chopped up into small pieces by enzymes

3)MHCII is made in the endoplasmic reticulum

4)MHCII is placed at the cell surface with the antigen for detection by T-cells

what does primary antibody responses start with 

IgM 

what must happen to make a more robust response 

must change the immunoglobulin class from IgM to IgG

what helps specify the ab class

the constant domain

Class-switch Recombination

Loop out and replace constant domain and replace with a new constant domain of a different class

what happens during a primary response

1. B cells multiply and produce IgM (first), then IgG (second) that bind to a particular antigen.

2. Memory B cells are produced to produce antibodies rapidly if the antigen is detected again (if you are reinfected)

what happens during a secondary response

1. Memory B cells respond to a specific antigen (reinfection) and multiply rapidly.

2. B cells produce some IgM and a high level (titer) of IgG antibodies to respond to infection.