Background For Immune Disorders Flashcards
What are the characteristics of antigens?
Usually protein or polysaccharides. Classified as either exogenous or endogenous.
What are antigens?
Macromolecule of natural or synthetic, capable of inducing and being recognised by immune responses such as antibodies and T cells.
Describe the classical pathway of complement activation.
Complement proteins are present in circulation and can be activated by a variety of mechanisms. Attached immunoglobulins can set off the “classical pathway”. The complement cascade can generate active compounds such as C3b that functions as an opsonin, or C5a that attracts neutrophils. If the C5-9 complex (the “membrane attack complex”) is generated, the cell to which the complex is attached can be lysed by perforation of its cell membrane.
What sets off the alternate complement activation pathway?
Bacterial products can set off the “alternate pathway”.
What are the characteristics of non-specific immunity? (Natural, native, innate immunity).
System in place prior to exposure to antigen.
Lacks discrimination among antigens
No immunological memory
Can be enhanced after exposure to antigen through effects of cytokines.
What are the characteristics of specific immunity? (Acquired, adaptive immunity)
Is induced and enhanced by antigen Shows fine discrimination - specificity Has immunological memory B cells - antibodies T cells - cytokines
What are the two pathways of adaptive immunity?
Cell mediated immunity by T cells:
CD8 T cells: direct lysis of target (infected) cells
CD4 T cells: production of cytokines that activate infected cells (e.g. Macrophages) to kill pathogens, help B cells for production of antibodies.
Humoral (antibody) mediated immunity by B cells:
Antibodies bind to whole or fractions of antigens outside cells.
Describe the primary and secondary antibody response.
Primary:
Takes days/weeks
IgM appears first, followed by IgG.
Secondary:
Activates memory B cells
Ab response detected within a day
Much higher Ab levels, higher IgG response.
What type of immune response is needed for extracellular and intracellular infections?
Extracellular (site of most bacteria) Elicits antibody (humoral) response
Intracellular (site of viruses and some bacteria, tumour cells)
Elicits cell-mediated response
Define active immunity.
Acquired through contact with antigen (e.g. vaccination, infection)
Define passive immunity.
Acquired by transfer of antibodies or sensitised lymphocytes (e.g. Antibody from mothers milk to baby).
What is the life cycle of lymphocytes?
Bone marrow and thymus (primary lymphoid tissues) produce B cells and T cells, respectively.
B cells and T cells recirculate through spleen and lymph nodes (secondary lymphoid tissues)
Antigen presenting cells (APC) pick up antigen and migrate to secondary lymphoid tissues and interact with lymphocytes.
What are cytokines?
Messenger molecules (polypeptides) Secreted by lymphoid and non-lymphoid cells Forms a mediator network, regulating the growth, differentiation and function of cells involved in immunity, hematopoiesis and inflammation.
What are the features of antibodies?
Produced by B cells and plasma cells
Specific to one type of antigen
Composed of four-polypeptide chain units with constant and variable structural regions
Two identical heavy chains
Two identical light chains, either kappa or lambda.
What are the functions of antibodies?
Opsonisation - Ab binds to pathogen surface molecules to be phagocytosed by macrophages.
Neutralisation - Ab neutralises toxins, binds to attachment molecules - so they are no more toxic, prevents cell entry.
ADCC: antibody dependent cell mediated cytotoxicity
Complement activation- occurs on antibody bound to pathogens - to be lysed.