Lymphocytes Flashcards
Severe combined immunodeficiency babies
Inability to clear infections
What does the adaptive immune system do
Improves the efficacy of the innate immune response
Focuses a response on the site of infection and the organism responsible
Has memory
Needs time to develop
Why type of response is T cells
Cell mediated response
What type of response is B cell
Humoral Response
What do the T cells do
Cytokines help shape immune response (CD4)
Kill infected cells (CD8)
What do the B cells do
Produce antibodies
Antigens
Moelcules that induce an adaptive immune response
What is the epitope
Region of an antigen which the receptor binds to
What type of antigen do T cells recognise
Linear epitopes in the context of MHC
Primary structure
What type of antigen does B cell recognise
Structural epitopes (3D structure)
Folding
What is clonal expansion
Interaction between a foreign molecule and that receptor leads to activation and clonal expansion
Differentiated effector cells will bear the same receptor
What is the antigen receptor diversity problem
Massive repertoire of lymphocytes receptors
Massive genes neeeded
How is antigen receptor diveristy generated through recombination
Functional genes for antigen receptors do not exist until generated during lymphocyte development
Immunoglobulin gene rearrangement
V and J area combined randomly and may sometimes overlap
Diagram of the T cell receptor
Recognises antigen fragments presented by other cells in the context of MHC
What is the major histocompatibility complex
Plays a central role in defining self and not self
Presents antigens to T cells
What is the MHC class 1
All nucleated cells
Single variable alpha chain plus a common beta microglobulin
What is the MHC class 2 complex
Only on professional antigen presenting cells
2 chains alpha and beta
Is the MHC polygenic
3 Class 1 loci and 3 class 2 loci
Expression is codominant
Why is matching people to surgery so important in MHC
Because each person can have up to 6 of each gene if completely heterozygous
How is the MHC1 complex loaded with antigen
Comes from intracellular pathogen
How is the MHC2 complex loaded with antigen
Extracellular antigen
How is the response to different pathogens orchastrated by the CD4 T helper cells
T helper cells produce cytokines
Cytokines have diverse actions on a wide range of cells
Th1 (pro-inflammatory, boost cellular immune reponse - fight off viruses)
Th2 (Pro-Allergic, boost muticellular repsonse)
What are Tfh
Pro-antibody
Works with B cells
IL-21
How do CD8 cells kill the targets
Programmed cell death - apoptosis
Fragmentation of nuclear DNA
CTL stores perforin, granzymes, granulysin in cytotoxic granules released after target recognition
Perforin - pore forming protein
Granzyme injected into cell through pores
How is the MHC1 complex loaded with antigen
Intracellular
What are the three many functions of antibodies
Neutralisation - prevent bacterial adjerence
Opsonization - promotes phagocytosis
Complement activation
What are the IgG antibodies role
Highest opsonization and neutralization activities
Classified by IgG1, IgG2, IgG3, IgG4
What are the IgM antibodies
Produced first upon antigen invasion
Increases transiently
What are the IgA antibodies
Expressed in mucosal tissues
Forms dimers after secretion
What are the IgE antibodies
Involved in allergy
Where do B cells come from
Derived from stem cells in bone marrow
Mature B cells are specific for a particular antigen
What is the BCR
Unique binding site which binds to portion of antigen called epitope
Made before cell ever encounters antigen
They can bind to soluble antigen
How do naive B cells be activated
From microbial constituents
From T helper cell
What is the role of thymus independent antigens
Directly activate B cells without the help of T cells
Often polysaccharide - repetitive structure
Second signal required is provided by microbial PAMP e.g. LPS
What type of antibody is only thrymus independently stimulated
IgM
No memory
What type of antibody is thymus dependent
Ig-classes
Memory
B cell activation by T cells
Membrane bound BCR recognises antigen
DC engulf antigen - not specific
Receptor-bound antigen is internalised and degraded into peptides
Peptides associate with self molecules (MHC class 2) and is expressed at cell surface
Tfh activated by MHC2 cell on DC
T cell finds B cell and produces cytokines which activate B cell
Becomes B plasma cell
