Antibodies Flashcards
Two different types of immune responses + definitions
innate- comprises of a genetically programmed set of responses that can be mobilised immediately upon infection
adaptive- immunity developed against one pathogen, providing a highly specialised defence
What mediates the adaptive immunity response?
Specific antigen receptors that bind to antigens on or produced by pathogens
different forms of antigen receptor
secreted or cell associated
antigen definition
a molecule that elicits an adaptive immune response
Immunoglobin definition
A large, Y shaped protein, produced mainly by plasma cells that is used by the immune system to neutralise pathogens and viruses, otherwise known as antibodies/ Ig
two types of antibody
B-cell associated
secreted- soluble in humour
What are T cell receptors?
protein complex found on the surface of T lymphocytes that are responsible for recognising antigens, however can never be secreted
What produce antibodies?
plasma cells, that differentiate from B-cells
Where are plasma cell sites for immunoglobulin synthesis?
gut, mammary gland, bone marrow, lymphoid organs
Role of antibodies
Bind to micro-organisms and prevent their entry into cells
bind to organisms and also to cells
assists phagocytes- opsonisation- and helps phagocytes neutralise bacterial toxins
activates complement and induces inflammation
membrane bound immunoglobulins act as a receptor for antigens
Explain binding to microorganisms
agglutination- antibodies glue together foreign cells into clumps that are attractive targets for phagocytosis
precipitation- antibodies glue together serum-soluble antigens, forcing them to precipitate out of solution into clumps that act as targets for phagocytosis
explain neutralisation
antibodies bind to regions of the bacterial cell or virion surface, preventing it from being able to enter the cell, thus neutralising it
define opsonisation
a molecular mechanism whereby molecules, microbes and apoptotic cells are chemically modified to have a stronger attraction to the cell surface receptors on phagocytes and natural killer cells
how do opsonins aid phagocytosis?
cell membranes have a negative charge- Zeta potential, which results in the cells repelling
opsonins bind to their targets, boosting the kinetics of phagocytosis by favouring interaction between the opsonin and cell surface receptor
inflammation definition
an ancient concept of medicine, that has been traditionally defined by the Latin words calor, dolor, rubor and tumor, heat, pain, redness and swelling
it is a result of the body’s working immune system and not the pathogen itself
Antibody structure
a glycoprotein made with two heavy chains and two light chains, bound together by disulfide bridges
the N- termini V light and V heavy domains act as the variable region, which contains the binding site
the rest of the Y-shaped molecule forms the constant region
Explain light chain structure
made of two domains Vlight and Clight which are formed of two different beta chains
What is the constant domain?
the other C domains, that have little or no sequence diversity within a particular class of antibody
What is the variable region?
the region where the polypeptide chains of different antibodies vary greatly in amino acid sequence
What two fragments can be formed by cleaving the antibody + where?
cleaved at the hinge region using proteases papain and pepsin
form 2 Fab- fragment antigen binding, because they bind the antigen
form 1 Fc - fragment crystalisable, because it readily crystallises
Fc function
mediates the effector functions of the antibody molecule by binding to serum proteins and cell surface receptors
formed of 4 constant heavy domains
Hinge function of IgG
Allows the two Fab molecules to adopt different spatial orientations relative to one another, which enables antigens spaced at different distances apart on pathogens to be bound tightly by one IgG molecule
Fab function
antigen binding region for specificity, formed of V light, V heavy, C light and C heavy
What are the different classes of immunoglobulins?
IgG, IgM, IgD, IgA and IgE
