B3: humoral and cellular adaptive immunity

what is an antibody?

proteins that circulate through the blood and recognize specific molecules, antigens

what is an antigen?

antibody generating

anything that can cause an antibody to be produced

• proteins, carbs, DNA, fats, other chemicals

antigens bind tightly and specifically to their antibody

what are immunoglobulins (Ig)?

antibodies

what are the multiple classes of Ig determined by?

constant regions of antibodies

what are the 5 mechanism of antibody action?

agglutination

opsonization

neutralization

activation of complement

antibody-dependent cell-mediated cytoxicity

what is agglutination?

antibodies glue multiple cells together that have the same antigen on surface

how is agglutination beneficial?

by binding to more than one antigen, pathogen are chained together and clump → bigger targets

• easier for neutrophils and macrophages to engulf them all and kill them

what is osponization?

phagocytes have an easier time grabbing pathogens that are coated with antibodies

• neutrophils and macrophages can engulf anything with an antibody on it

what is neutralization?

if the antigen is biologically important, binding of the antibody may shut it down

how does neutralization work?

antibody binds to viruses and toxins → directly affects the pathogen

shuts down the virus’s and toxin’s ability to enter the cell

what is activation of complement?

antibodies attract the complement system, which can lyse bacterial cells and signal for inflammation

what is antibody-dependent cell-mediated cytotoxicity?

antibodies attract granulocytes to attach and try to kill whatever they’re stuck to (self cells, large pathogens)

granulocytes dump their toxic contents on the outer surface of the parasite

what are B cells? how are they related to antibodies?

produce antibodies and are made in our bone marrow

where are B cells found?

circulate in our blood and lymph

how many antibodies does a B cell produce?

each B cell produce one and only one type of antibody

how are so many antibodies produced?

cells that produce antibodies use recombination to make variants

how do cells use recombination to make antibodies?

regions that code for the variable region of anitbodies are built with short regions of DNA that are very similar

as a B cell matures → splices out bits from the different regions

what are the first stages to produce an antibody?

naive B cells carrying specific antibodies are produced

variants are made without knowing that they’re useful

huge population of different B cells in the blood/tissues

what is the second stage to produce an antibody?

naive B cell comes across an antigen that matches its antibody, and undergoes clonal selection

B cell is activated, selected for growth → become a long-term part of the immune system

what is the third stage to produce an antibody?

some B cells become plasma cells to produce large amounts of soluble antibody in the blood

some become memory cells to “remember” a pathogen later

what is clonal selection?

population of the B cell that came across an antigen that matched its antibody expands

produce memory cells and plasma cells

what are memory B cells?

keep the antibody on their surface

act as sensors

take up long-term residence in your lymphatic tissues, blood, and various organs → for long-term responses

what are plasma B cells?

secrete antibodies into blood and lymph

these are the antibodies we find in your blood

what would a graph of antibody production look like after an initial exposure to antigen? a second or later exposure?

why are the responses different?

later responses are stronger and faster than early ones because of the memory cells

initial response:

• don’t have a strong antibody response

• eventually recover because naive B cells got clonally selected and started producing more antibodies

second response:

• you have memory cells now → large B cell population

• immediately starts producing large amounts of antibodies

what are T cells?

produced in the marrow and mature in the thymus

circulate in our blood and lymph

what do T cells carry? what are they similar to?

each T cell carries one type of T cell receptor (TCR)

TCRs are very similar to antibodies → same structural components

how are TCRs and antibodies different?

TCRs are never made in a secreted form → always associated with a T cell

how are T cells like B cells?

like B cells, T cells that “see” a matching antigen are amplified and will respond faster/stronger to later infections

how are T cells and B cells different?

antibodies can’t deal with intracellular pathogens, but T cells can (memory T cells)

what are helper T cells?

immune system coordinators

• respond to TCR binding by sending out chemicals signals

• help activate B cells, cytotoxic T cells, macrophages, etc.

• serve as a crucial central regulator of the immune response

what are helper T cells a primary target of?

HIV

what are memory T cells?

long-lived cells produced after TCR exposure to antigen

create more rapid responses to future exposures

what do cytotoxic T cells do?

scans our own cells for improper proteins

how are cytotoxic T cells similar to NK cells?

CT cells probe our own cells

how are CT cells different NK cells?

CT cells are looking for a specific match to their TCR (specific response)

• only go after a cell with a binding partner to their T cell receptor

• inject its granules → stops viral infection

what sorts of infections are cytotoxic T cells particularly good at combating?

provides good defenses against viruses, intracellular bacteria

how do various cell types attack larger pathogens?

many immune cell types recognize bound antibodies

release toxic granules/lysosomes to attack pathogens

is the attack of larger pathogens from humoral or cellular systems, or both?

both