immunity and response to infection Flashcards
pyrogens
peptides secreted by leukocytes and act on hypothalamus inducing fever which inhibit iron uptake by bacteria
interferons
proteins that modulate immune response and act as antiviral agents
complement proteins
plasma proteins that destroy cells
phagocytes
immune cells that can digest foreign antigens
neutrophils
type of WBC that are the first line of action at site of infection
monocytes
monocellular phagocytes in the blood, differentiate into macrophages in tissues
microglia
CNS resident and help maintain homeostasis
dendritic cells
derived from monocytes - found in tissues like lymph
antimicrobial function of phagocytes
phagocytic cell is attracted to and recognises microbes as being foreign via surface receptors
it extends filopodia engulfing the microbe and phagosomes begin to form
once contained in a phagosome, fusion with a digestive enzyme containing lysosome occurs
chemotaxis
chemical attractants from invading bacteria and tissue leukocytes attract local neutrophils and monocytes from blood stream
diapedesis
mast cells and basophils release histamine making the blood vessel permeable and allowing cells through
antigens
usually high MW substances and contain epitopes
haptens
carrier molecule protein that binds to low MW compounds and illicit an immune response
ex: penicillin can act as a hapten in some patients which can lead to severe reaction called anaphylaxis
opsonisation
the coating of foreign antigens by antibodies making them attractive to neutrophils (natural killer cells and macrophages)
opsonin
protein which promotes opsonisation
neutralisation
bacterial toxins are neutralised by antibodies e.g. diptheria, tetanus, botulinumtoxin
complement cascade
- The classical pathway: C1 recognises microbial surface
- The lectin pathway: initiated by soluble carbohydrate binding proteins that bind to carbohydrate structures on microbial surfaces
- The alternative pathway: initiated by spontaneous hydrolysis and activation of C3
- C3 convertase cleaves C3 into C3b and C3a (peptide inducing inflammation)
C3b binds to microbial surfaces and acts as an opsonin - C5 convertase cleaves C5 into C5a and C5b
- C5b initiates the interaction to form membrane attack complex (MAC) on the pathogen surface
-creating a pore in the cell membrane that leads to cell lysis due to osmotic shock
B-cells
- plasma B cells produce antibodies
- memory B cells lead secondary immune response
- B-cells are activated when free antigens bind to immunoglobulin (IgM/IgD) receptors on the B-cell surface
- during infection binding of antigens to B or T cells triggers clonal proliferation
clonal proliferation
- antigen binds to B-cell via IgR activating it
- T-cell moves to B-cell activates it
- activated B-cell proliferates
- differentiating into antibody producing plasma cells or memory cells
helper T-cells
release interleukins and activate macrophages and cytotoxic T-cells (Th1)
they also activate B-cells and help recruit neutrophils and macrophages
regulatory T-cells
dampen immune response
memory T-cells
increase longevity of immunity
cytotoxic T-cells
directly kill infected cells
T-cell activation
- class 1 major histocompatibility complex (MHC) proteins activate CD8 + cytotoxic T-cells
- class 2 major histocompatibility complex (MHC) proteins activate CD4 + helper T-cells
Th-cell + B-cell activation
- activated Th-cell finds B-cell that recognises its peptide antigen forming an immunological synapse
- Th-cells release cytokines which stimulate further B-cell production of antibodies (IgE)
