what happens when an active B cell encounters an antigen?
1) produces antibodies
2) antibodies label antigen
3) labelled antigen binds to the antibody receptor on a macrophage
4) macrophage engulfs antibodies & bacterium
5) lysosomes fuse with vacuole & release digestive enzymes which destroy the bacterium
what does an antibody look like?
how are macrophages involved in the activation of T helper cells?
1) bacterium engulfed by macrophage
2) macrophage becomes an APC
3) APC binds to a T helper with a complementary CD4 receptor -the T helper is activated & divided
4) produces clone of T memory& active T helpers
What happens when a B (w/ complementary receptors) cell binds to a bacterium with antigens on its surface?
1) bacterium with antigens on surface binds to a B cell with a completely receptor -becomes APC
2) APC binds to an activated T helper & produces cytokines (which stimulate B cell)
3) B cell divides to produce B memory clones & B effector clones
4) B effectors differentiate into plasma cells (which secrete antibodies)
what do B effector cells do?
- differentiate to produce plasma cells, which release antibodies into the blood and lymph
- short lived, last a few days
what do B memory cells do?
-remain in body for months/years, enable an individual to respond more quickly to the same antigen in the future
how do T killer cells work?
1) bacterium infects cell of host
2) cell presents antigens & becomes APC
3) T killer with a complementary receptor binds to APC
4) cytokines stimulate differentiation into active T killers & memory T killers
5) active T killer binds to APC
6) T killer releases chemicals that cause pores to form in the infected cell - infected cell dies
what does the secondary immune response involve?
memory cells (only takes 2-7days)
- > B memory cells can differentiate immediately to produce plasma cells
- > invading pathogens are destroyed so quickly that the person is often unaware of symptoms ( said to be immune )
why can we distinguish between our own cells & of foreign invaders?
some of the membrane proteins on the surface of our cells & mark the body as ‘self’
what happens for lymphocytes for ‘self’ membrane proteins?
- destroyed by apoptosis (programmed cell death)
- only lymphocytes with receptors for ‘non-self’ antigens remain
why does the body sometimes attack itself?
particular cells may alter in some ways so they appear ‘foreign’ and get destroyed by the immune system (ie. rheumatoid)
what causes TB?
Mycobacterium tuberculosis
what are the most common forms of TB?
respiratory or pulmonary
how many people closely exposed to TB get infected & how many of those develop symptoms?
30%
5-10%
what is the first phase of TB?
primary infection ( several months & may have no symptoms )
what happens in TB primary infection?
M.tuberculosis causes an inflammatory response:
- macrophage engulfs bacteria
- granuloma (mass of tissue) forms -in TB these are anaerobic & have dead bacteria and macrophages in the centre
- called tubercules
- after 3-8 weeks, the infection is controlled & infected region heals
where can M.Tuberculosis survive?
inside macrophages
- > they have very waxy & thick cell walls which make them very hard to break down
- > they can lie dormant for years
what can TB do to T cells?
suppress them
->reduces antibody production & attacks by T killer cells
what is the 2nd phase of TB?
active TB
- > occurs if the patient’s immune system cannot contain the disease when it first arrives in the lungs
- > the no. of bacteria is too great OR an old infection may break out
why may the activity of the immune system be reduced?
- old age
- young
- malnutrition
- poor living conditions
- AIDS
what does active TB do in the lungs?
multiply rapidly & destroy the lung tissue , creating holes.
-> eventually kill the patient
what are symptoms of active TB?
- coughing
- shortness of breath
- loss of appetite
- weight loss
- fever
- extreme fatigue
what happens with fever?
- fever-causing substances released from neutrophils/macrophages
- affect hypothalamus- raises core body temp (40.5º)
- raised temp enhances immune function &phagocytosis
- bacteria &viruses may reproduce more slowly at higher temps
what is the main symptom of glandular TB
-enlarged lymph glands (neck/armpits)
