Lecture 6: Antibodies in Infection Flashcards
How do foreign antigens meet the adaptive immune system (lymphocytes)
Antigens are phagocytosed by localised phagocytic cells which leave the tissue and enter the lymphatic system to the secondary lymph organs where specialised antigen presenting cells use MHC proteins on their surface to present antigens to the specific receptors on lymphocytes.
What lymphocytes are regulators
-CD4 T lymphocytes by producing cytokines
Which lymphocytes are effectors
- B lymphocytes (produce antibodies)
- CD8 T lymphocytes with antigen specific toxicity
- Antibody dependent cell mediated cytotoxicity (K cells) help b lymphocytes
- NK cells
What are the 3 ways recognition can be established
- common characteristic : non specific
- particular microbe characteristic : specific
- common characteristic in uncommon context
Compare the ways that B lymphocytes and T lymphocytes bind to antigen to generate an internal signalling pathway leading to them becoming an effector
B cell: receptor is a surface immunoglobulin (antibody) which binds antigen directly whereas for T cell its a Tcell receptor which needs to be stimulated by other cells presenting the antigen.
B cell has CD79 signal transduction molecules and T cell has Cd3 “” molecule.
What antigens are recognised by b and t cells
B cells recognise a wide range of antigenic substances but T cells can only recognise short peptide antigens
Describe immunological cross reactivity for b and t cell surface receptors
It is the property of surface receptors to be able to induce a signal even if its not a perfect fit (can be med or low affinity depending on conc of antigen) so a finite number of b and t cells can still get activated by a infinite number of antigens
Whats the other word for antigen
Epitope
Describe the structure of an antibody
2 heavy chains and 2 light chains held together by disulphide bonds and non covalent interactions. The arms of the Y have variable (antigen binding sites same on each arm)
and the feet are made of constant (biologically functional regions) where phagocytic cells bind to (Fc). Part of this constant region is a complement binding region under the hinge.
From when after birth does the concentration of baby’s own antibodies start to overtake the adoptively transferred immune response from maternal antibodies transferred in utero and trapped in breast milk
2 months after birth
Describe the principle of immunisation by defining primary and secondary antibody response
Primary response is to an antigen not previously exposed to. There is a lag before antibodies are in the blood neutralise the antigen
-Primary response decays with absence of antigen
SEcondary response is to same antigen later in life. This is rapid and vigorous and decays slower.
What happens to B cells at the primary response that leads to 2ndary response later
Antigen in 2ndary lymphoid organs will bind to a Virgin b cells that has the antibodies with high enough affinity to activate it. It will recieve activation signals from a helper T lymphocytes which lead to proliferation and maturation of plasma cells which secrete the same antibodies in the blood as well as memory b cells which live long and go to every 2ndary lymhoid organ ready to produce secondary response which no longer needs helper T cell signals
What are the 4 ways that antibodies help
- Direct neutralisation by physically blocking the viruses ability to bind to target cell and infect
- Opsonisation: coating the bacterium in antibody bc phagocytes have high affinity to the fc region of antibody
- Antibody dependent cell mediated cytotoxicity called K cells deliver short range cytotoxicity to antibody covered antigen
- Complement activation:
What are the two pathways to the complement cascade and what are the main effects of it
Classical pathway is activated by antigen-antibody complexes whereas Alternative pathway is formed by pathogen surfaces.
The C3 convertase part of the early components cleaves C3, leading to
1. C3a–> vasodilation, chemotaxis
2. C3b opsonisation and later part of later component assembly into membrane pore for membrane lysis
What type of immunity is the product of b cells and effective against antigens on the outside of cells (bacteria, stopping attachement of viruses and toxins) and what is the other type of immunity
Humoral immunity - has antibodies.
the other immunity is Cell- mediated- no antibodies and is effective against intracellular antigens (eg virus infected cells, tumour, transplanted organs)
