lymphocytes Flashcards
what are innate immune cells?
macrophage: eats stuff
neutrophil: kills stuff
what are adaptive immune cells/
T cell: orchestrates immune response/kills infected cells
B cell: makes antibody
what is adaptive immunity?
tailored response to a specific antigen
involves expansion of antigen specific lymphocytes
forms memory cells –> long lasting immunity
why do we need adaptive immunity?
to clear infecttions
protects from repeat infections with same pathogens
give a problem of adaptive immunity
autoimmunity
When is an adaptive immune response generated?
Once the pathogen overwhelms innate defense mechanisms
what’re the 2 types adaptive immune response?
T cell: cell mediated response
B cells: humoral response
what do T cells do?
produce cytokines to help shape immune response (CD4)
kill infected cells(CD8)
what do B cells do?
produce antibodies
what is an antigen?
molecule that induces an adaptive immune response (mostly protein)
what is an epitope?
region of an antigen which the receptor binds to
how does clonal expansion occur?
interaction between foreign molecule and specific receptor on lymphocyte –> activation and clonal expansion
what is the antigen receptor diversity problem?
to deal with antigen diversity needs encode a massive repetoire of lymphocyte. receptors
would need 10^15 Dif genes cogenerate 10^15 dif antibody molecules
how is antigen receptor diversity generated?
by recombination
when do function genes of antigen receptors exist?
not until they are generated during lymphocyte development
what are the 3 BCR chains?
kappa, lamda, heavy chain genes
what encodes each BCR receptor chain?
separate multigene families on Dif chromosomess
what happens to gene segments during B cell maturation?
rearranged and brought together
how is the diversity of the lymphocyte repertoire created?
immunoglobulin gene rearrangement
what does the TCR do?
recognises antigen fragments presented by other cells in the context of MHC
what is the major histocompatibility complex (MHC)?
plays a central role in defining self and non-self
presents antigens to T cells
critical in surgery and donor matching
give features of MHC class I
all nucleated cells, although at various levels
has a single variable alpha chain and a common beta micro globulin
what do T cells recognise?
linear epitopes, MHC class I
what do B cells recognise?
tertiary structure of the protein
what is the MHC?
major histocompatibility complex
what is the main purpose of B cells?
make antibodies
what are the 3 core protective roles of antibodies?
- neutralisation
- opsonisation
- complement activation
how does antibody neutralisation work?
antibody prevents bacterial adherence
how does antibody opsonisation work?
antibody promotes phagocytosis
how does complement activation work?
antibody activates complement, which enhances opsonisation and lyses some bacteria
what is complement?
a cascade of immune responses
what are the 5 antibody classes?
IgG, IgM, IgA, IgD, IgE
describe IgG
main antibody found in blood
highest opsonisation and neutralisation activities
classified into 4 subclasses (IgG1, IgG2, IgG3 and IgG4)
memory antibody
describe IgM
produced first upon antigen invasion, increases transiently
less specific but more sticky than IgG
make IgM earlier, then switch to IgG
describe IgA
expressed in mucosal tissues
forms dimers after secretion
describe IgD
unknown function
describe IgE
involved in allergy
what’s the difference between the different classes of antibodies?
different constant region
affects the type of receptors it binds to
what are B cells?
white blood cells
lymphocytes
effector cells of humoral immunity –> secrete antibodies
memory B cells (prevent repeat infections)
where are B cells derived from?
stem cells in the bone marrow
where do B cells migrate into?
the circulation (blood, lymphatic system) and into lymphoid tissues
what does the unique binding site on the BCR do?
binds to a portion of the antigen called antigenic determinant or epitope
when is the BCR made?
before the cell ever encounters antigen
how are B cells different to T cells?
don’t need MHC to present antigen
B cells can bind soluble antigens
how do B cells make antibodies?
need to communicate w a T cellls
s
naive antigen-specific lymphocytes (B or T) can be activated by antigen bone.
naive B cells require accessory signal.
- directly from microbial constituents
- from a T helper cell
what are the 2 pathways by which antibody production by B cells is achieved?
ones that require T helper cells (thymus dependent)- all Ig-classes memory
ones that don’t require T helper cells (thymus independent)- only IgM, no memory
what do T independent B cells recognise?
sugar molecules, polysaccharides, needs to have a repetitive structure
BCRs cluster together, activating immune response
how does B cell activation by T cells work?
- the membrane bound BCR recognises antigen
- the receptor-bound antigen is internalised and degraded into peptides
- peptides associate with ‘self’ molecules (MHC class II) and is expressed at the cell surface
- this complex is recognised by matched CD4 T helper cel
- B cell activated
what does MHCII do?
samples the environment and chops the cell up into smaller pieces
give features of MHC class II
normally only on ‘professional’ antigen presenting cells
has 2 chains: alpha and beta
give features of MHC gene expression
encoded by HLA genes in humans
MHC is polygenic: 3 class I and class II loci
more than 17,000 MHC variants
expression is co-dominant (maternal and paternal genes both expressed)
so ech person can have up too 6 of each gene if completely heterozygous
