humoral immunity - block d Flashcards
two arms of the immune system
cell-mediated immunity
antibody-mediated immunity
humoral activation
phagocytosis of pathogen by antigen presenting cells
antigen processing/presentation
educate naïve t cell
clonal expansion t cell
humoral effector phase
uptake of pathogen by b cell
antigen processing/presentation
interaction with antigen-specific t cell
clonal expansion of b cell and plasma cell differentiation
antibodies
glycoprotein molecules
antibodies can only attach to their specific antigen
produced by b lymphocytes
recognises proteins, carbohydrates, nucleic acids, glycolipids and small inorganic molecules
can mediate a number of responses:
- interact with complement
- interact with phagocytotic cells (via Fc portion of antibody)
antibodies polypeptide chains
consist of four polypeptide chains
two identical light chains
two identical heavy chains - determines the isotype class of antibody
antigen binding region made up of both of the light and heavy chains - 2 antigen sites per antibody
antibody classes
there are 5 antibody classes distinguished by their structure and physiological role
IgG, IgD, IgE, IgA, IgM
IgA
monomeric and dimeric form
dimeric IgA can survive on mucosal surfaces
most IgA is present in the gut - produce 50 mg/kg/day
selective IgA deficiency - most commo primary Ab deficiency - IgA –deficiency can appear asymptomatic
IgA important in defence against intestinal such as pathogen such as rotavirus
IgA present in genital urinary tract secretions can protect protect against HIV - neutralise viral particles
transported into the guy lumen through epithelial cells at the base of the crypts
dimeric IgA binds to the layer of mucus overlying the gut epithelium
IgA in the gut neutralizes pathogens and their toxins
IgG
secreted later in the primary response and is the main antibody class in the secondary response
gives long term protection, cross the placenta to provide neonatal protection until the baby’s immune system develops
75% of circulating Ig
mediates in phagocytosis and opsonisation
mediates i antibody-dependant cellular cytotoxicity by NK cells
mediates in degranulation of neutrophils, eosinophils and mast cells
IgM
the first antibody class secreted in the primary response and has a short half-life
present in new born babies – natural IgM
produced in response to antigenic stimulation of B cells – adaptive IgM
can recognise a wide range of different microbial components - viral antigens and bacterial toxins
high avidity of polymeric IgM – means its can immobolise target at a site – stop bacteria spreading
IgE
originally evolved as a protection against worm infestations but in first world countries is mainly associated with type 1 allergic reactions
mediated via degranulation of granulocytes
IgE-mediated activation occurs through FcεRI on mast cells and basophils/multivalent antigens cross-link the receptor-bound IgE to trigger degranulation and the release of pre-formed mediators
pro-inflammatory response induces a T helper 2 (Th2) immune response.
specific IgE bound to mast cells recognises specific antigen in the venom - IgE activation causes mast cell degranulation and release of enzymes that inactivate the venom
role of cytokines
IL-4 - inhibits IgM, IgG3, and IgG2a, induces IgG1 and IgE, no effect on others
IL-5 - augments production of IgA
IFN-y - inhibits IgM, IgG1, and IgE, induces IgG3 and IgG2a
TGF-b - inhibits IgM, and IgG3, induces IgG2b, and IgA
IL-21 - induces IgG3, IgG1 and IgA
pathogens/infections can modulate cytokines present
antibody effector functions
neutralise (masks pathogen binding site to host cells)
agglutinate (clump together – Ab and pathogen)
opsonisation (from Greek – means make tasty)
activate complement cascade
antibody-dependent cell-mediated cytotoxicity (ADCC)
trigger degranulation of granulocytes
T-independent response
T independent responses are fast because B cells are directly activated by antigens with certain types of structure
the only antibody class that can be produced is IgM (no T cell help to class switch)
short life-span and are not protective BUT for some organisms do provide a first line of defence
do NOT make memory cells
T-dependent response
in the immune response to TD antigens, T lymphocyte help to B lymphocytes is essential for the regulation of B lymphocyte proliferation, production of immunoglobulins, immunoglobulin class switching, rescue of B lymphocytes from apoptotic death, germinal centre formation, and generation of B lymphocyte memory.
immunological memory
the first time the immune response ‘sees’ an antigen it is called the PRIMARY RESPONSE
the second and all the subsequent times it ‘sees’ the same antigen it is called the SECONDARY RESPONSE
secondary responses are bigger and faster because of the formation of MEMORY CELLS
MEMORY CELLS remember each antigen encountered, thus subsequent responses are faster and more powerful
this is the basis for protective vaccination against infectious diseases
