6.3- the response to infection Flashcards
two main types of leucocytes
-leucocytes are white blood cells
-the two main types are granulocytes and agranulocytes
what are non specific responses?
-physical, chemical and mechanical barriers, they attempt to prevent entry of all pathogens
-there are also non specific responses which are a part of innate immunity
-these are biological responses in the blood such as inflammation
what is inflammation?
-eliminates invading pathogens by activating the second line of defence
-leucocytes such as macrophages are drawn to the infected area they ;
1.fight and eliminate pathogen
2.initiate tissue repair
-inflammation causes fever heat and swelling, signs the immune system is working
what is happening in inflammation?
-when the tissue is damaged, mast cells and basophils release chemicals known as histamines
-histamines cause blood vessels in the area to dilate causing heat and redness
-raised temp reduces effectiveness of pathogens in the area
-histamines make cells forming wall of capillary separate slightly
-plasma containing leucocytes and antibodies is forced out, causing swelling and pain
fevers
-when infected, the hypothalamus raises our body temperature to inhibit bacterial growth
-however, prolonged temp above 40 can be damaging to tissues and extensive water loss can be deadly
what are mast cells?
-part of inflammatory and allergic response
-they reside in the skin and mucosal tissue, becoming activated when they come in to contact with foreign antigens on pathogens
when activated they release histamines stored in their granules
phagocytes
-e.g. macrophages and neutrophils
-phagocyte engulfs the pathogen to form a phagosome (phagocytosis)
-lysosomes release enzymes (lysozymes) into the phagsome that hydrolyse proteins and lipids to digest and destroy pathogen
the specific immune response
-targets specific pathogens
-Each T and B cell is tailored towards a specific pathogen and not effective towards any others
four key features of specific immunity
1.can distinguish self from non-self
2.specific to each foreign cell
3.diverse, can recognise potentially any foreign antigen
4.immunological memory-secondary response is rapid
humoral response
-immune response to pathogens (and their antigens) free in tissues and the bloodstream, involves specific antibodies
cell mediated response
-response to own body cells that have altered self- antigen
-i.e. cells that have become infected by a virus or become cancerous
MHC
-major histocompatibility complex
-molecule found on the cell surface membrane of all cells used to present antigens
-cells of immune system recognise these as self antigens and leave these cells alone
antigen presenting cells
-phagocytic cells are known as APCs
-after they engulf and digest pathogens they present parts of the pathogen (antigens) on their surface attached to MHC molecules
what happens in phagocytosis
1.phagocytes engulf pathogen
2.pathogens are engulfed into phagosome
3.phagosome fused with lysosome where they are digested
4.cytokines released from phagocytes to stimulate other phagocytes in the area
how to APCs activate T cells
-antigens are presented to T cells and their T cell receptors, this then activates those cells
-activated T cells divide by mitosis, creating many more copies of each specific T cell
where are T cells made and matured
-made in bone marrow but mature in thymus gland
helper T cells
-each different helper T cell has a unique T cell receptor on its surface that fits a specific antigen
-T cells can only recognise antigen presented to them on MHC from an antigen presenting cell
-activated T cells divide rapidly by mitosis, creating many clones, they then;
-develop memory cells
-stimulate phagocytes
-stimulate B cells
Killer T cells
-Killer T-cells can attack body cells which have been antigenically altered by viruses or cancer cells.
-they destroy the pathogen causing cell lysis
where are b cells made and matured-
-in the bone marrow
-they produce antibodies that target specific pathogens
what do B cells do
-produce antibodies which recognise antigens
-each b cell produces a unique antibody on its surface, each a specific shape to recognise an antigen
-antibody binds to antigen and neutralises it
3 ways antibodies can act;
1.agglutination
2.opsonisation
3.neutralisation
antibodies- agglutination
-when antibodies bind to the antigens on pathogens, the microorganisms agglutinate/ clump together
-this helps to prevent them spreading through the body and makes it easier for phagocytes to engulf them
antibodies-opsonisation
-the antibody acts as an opsonin, a chemical which makes an antigen or pathogen more easily recognised by phagocytes
antibodies-neutralisation
-antibodies neutralise the effects of bacterial toxins by binding to them
T cell dependent activation of B cells
1.a B cell antibody receptor matches with complementary antigen. A B cell internalises the antigen and presents it on its surface, a bit like an APC
2. an activated T cell binds to the B cell via this presented antigen
3.T cell produces cytokines which activate the B cell
B cell activation
-after activation, the B cell divides by mitosis to produce memory B cells and B effector cells
-B effector cells eventually differentiate into antibody producing plasma cells
T killer cell activation
- an APC digests and engulfs pathogen and presents on surface via MHC
2.T Killer cell with complementary T cell receptor binds to the MHC/antigen on the APC.
3.using cytokines from activated T helper cell, killer t cell becomes activated
4.active T killer and T memory cells are formed
5.T killers release perforin chemicals, these create holes in infected cell and cause cell lysis
primary Vs secondary immune response
primary- slow weak- Helper T cells activated.
Killer T cells cause cell lysis, B cells are activated, divide, form plasma cells and produce antibodies. Memory B and T cells left behind
Secondary- use of memory cells, no symptoms of infection
artificial passive immunity
-Passive immunity is when antibodies are introduced from outside the body, you do not have to make them yourself
-Can be used if there isn’t a vaccine ready yet, or if someone requires a tetanus injection or requires antibodies for a snakebite
-immediate but only short term
natural passive immunity
-e.g. when and infant receives a mothers antibodies through placenta or breast milk
active immunity
-exposure to a pathogen or antigen
-either through natural exposure or vaccination
vaccination
-aims to stimulate a primary immune response without actually causing disease like a normal infection
-allowing people to safely develop memory cells
