packet 12 Flashcards
built into cell membrane of all cells except red blood cells
MHC-I molecules
function of MHC
if cell is infected with virus MHC-I contain bits of virus marking cell so T cells recognize is problem
if antigen presenting cells (macrophages or B cells) ingest foreign proteins, they will display as part of their MHC-II
MHC-II markers seen only on membrane of
antigen presenting cells (macrophages, B cells, thymus cells)
bind to antigen in extracellular fluid
b cells
can only recognize fragments of antigens that have been processed and presented to them as part of a MHC molecule
t cells
“see” antigens if part of MHC-II molecules on surface of antigen presenting cell
helper t cells
“see” antigens if part of MHC-I molecules on surface of body cells
cytotoxic t cells
Foreign antigen in body fluid is phagocytized by
APC (macrophage, B cell, dendritic cell (Langerhans cell in skin)
Antigen is digested and fragments are bound to MHC-II molecules stuck into
antigen presenting cell membrane
APC migrates to lymphatic tissue to find
t cells
Small protein hormones involved in immune responses are secreted by
lymphocytes and antigen presenting cells
alpha-interferon used to treat Kaposi’s sarcoma, genital herpes, hepatitis B and C & some leukemias
beta-interferon used to treat multiple sclerosis
interleukin-2 used to treat cancer (side effects
Cytokine therapy uses cytokines (interferon)
Begins with activation of T cell by a specific antigen
Result is T cell capable of an immune attack
elimination of the intruder by a direct attack
cell-mediated immunity
Types of Mature T Cells
Helper T cells
Cytotoxic (killer) T cells
Memory T cells
Display CD4 on surface so also known as T4 cells or TH cells
Recognize antigen fragments associated with MHC-II molecules & activated by APCs
helper t cells
Function is to costimulate all other lymphocytes
secrete cytokines
helper t cells
function in that it costimulates itself to proliferate and secrete more interleukin (positive feedback effect causes formation of many more helper T cells)
autocrine
Display CD8 on surface
Known as T8 or Tc or killer T cells
Recognize antigen fragments associated with MHC-I molecules
Costimulation required by cytokine from helper T cell
Cytotoxic T Cells
T cells from a clone that did not turn into cytotoxic T cells during a cell-mediated response
Available for swift response if a 2nd exposure should occur
memory t cells
Millions of different B cells that can recognize different antigens and respond
B cells sit still and let antigens be brought to them
stay put in lymph nodes, spleen or peyer’s patches
Once activated, differentiate into plasma cells that secrete antibodies
Antibodies circulate in lymph and blood
Antibody-Mediated Immunity
B-cells are also drawn to a pathogen by
complement proteins
Antibodies circulate in lymph and blood
combines with epitope on antigen similarly to key fits a specific lock
80% of plasma Ab’s, enhances phagocytosis, neutralizes viruses, protects newborn
IgG
10% of plasma Ab’s, first produced during infection, neutralizes bacteria, agglutinates
IgM
0.2% of plasma Ab’s, D = Don’t know
IgD
15% of plasma Ab’s, only mucosal surfaces
IgA
0.002% of plasma Ab’s, allergic reactions (work with basophils and may fight parasitic worms / activate eosinophils)
IgE
first exposure to antigenresponse is steady, slow
memory cells may remain fordecades
Primary immune response
1000’s of memory cells proliferate & differentiate into plasma cells & cytotoxic T cells
antibody titer is measure of memory (amount serum antibody)
recognition & removal occurs so quickly not even sick
Secondary immune responsewith 2nd exposure
must learn to recognize self (its own MHC molecules ) & lack reactivity to own proteins
self-recognition & immunological tolerance
t cells
those can’t recognize self or react to it
destroyed by programmed cell death (apoptosis or deletion)
inactivated (anergy) – alive but unresponsive
only 1 in 100 emerges immunocompetent T cell
t cells
