2.02 - Immune Responses To Encapsulated Bacteria Flashcards
What are the key steps involved in phagocytosis?
Binding of pathogen to phagocyte Pathogen internalised in phagosome Phagosome fuses with lysosomes, which contain antimicrobial factor Microbial death
What is the difference between direct and indirect phagocytosis?
Indirecty phagocytosis is when either antibody (opsonisation), complement or some other process signals the macrophage (or other phagocyte). Direct is when pattern recognition receptors bind bacterial pathogen associated molecular patterns
What are the three methods of evasion of phagocytes?
Prevent encounter with phagocyte –>eg. C5a peptidase prevents Avoid recognition and attachment –> capsule, m protein, fc receptors Survive in phagocyte and be released from phagosome
What is the difference between Thymus-independent type 1 and type 2 responses?
TI1: Not involving spleen. TI-1 response activates both naïve and mature B cells in response to lipopolysaccharide. Directly induces B cell proliferation. TI2: Involves spleen. Molecules with highly repetitive pattern such as bacterial polysaccharide and viral envelopes. Only occurs in mature B cells in spleen marginal zone. IgM and IgG produced by marginal zone B cells bind to the bacterial capsule and mediate phagocytosis
Provide example of PAMPS for gram positive and gram negative bacteria
Gram positive: Peptidoglycan, lipoteichoic acid Gram negative: lipopolysaccharide
Describe the Thymus Independent immune response
Capsules hide bacterial targets of phagocytic receptors preventing them from being ingested and thus able to replicate. Humans have developed a T cell/Thymus Independent response to counteract this bacterial strategy.
What is the marginal zone?
Unique to the spleen Highly organised region Rich in macrophages Contains marginal zone B cells
Compare TI-2 and thymus dependent responses with regards to:
Trigger, T-cells required, location of antibody production, memory, class switching and level of affinity
