Block B lecture 1 Flashcards
what is the immune system ?
this is the tissues, cells and molecules that protect the body from infection.
what is the innate immunity ?
the early phase of the host response activated first when exposed to a pathogen
- Present in all individuals at all times
- Does not increase with repeated exposure to a pathogen, always the same response.
- Discriminates between groups of pathogens, rather than closely related individual pathogens.
- Predates separation of animal and plant lineages
what is the adaptive immunity ?
is generated by specific lymphocytes
- Discriminates between individual pathogens even if they are extremely closely related
- is associated with “immunological memory”, when exposed to the same pathogen for a second time this provides a quicker response that is more efficient.
- It appears abruptly in evolution in the cartilaginous fishes such as sharks and sting rays.
what is the first line of defence ?
The first is the anatomic barrier provided by the body’s epithelial surfaces which act as a physical barrier to prevent pathogen infection.
2nd ?
various chemical and enzymatic systems, including complement, act as an immediate antimicrobial barrier near these epithelia, these will come into effect if the first barrier is breached. C3 is part of the complement system.
if the epithelial are breached then what occurs to provide a rapid cell mediated defence ?
nearby various innate lymphoid cells can coordinate a rapid cell-mediated defence. This includes macrophages, granulocytes and NK cells.
inflammatory inducers ?
are chemical structures that indicate the presence of invading microbes or the cellular damage produced by them. Bacterial lipopolysaccharides are produced by gram negative bacteria cells, this is a host defence that activates an immune response. When ATP is present this activates the immune response as it is normally found within a cell not out with it.
sensor cells ?
include macrophages, dendritic cells and neutrophils which detect these inducers by expressing various innate recognition receptors, and in response produce a variety of mediators that act directly in defence or that further propagate the immune response.
what do the PRR’s of the innate system do ?
he pattern recognition receptors (PRRs), detect distinct evolutionarily conserved structures on pathogens, termed pathogen-associated molecular patterns (PAMPs). The binding of the PAMP to the PRR activates the immune response.
mediators ?
include many cytokines, and they act on various target tissues, such as epithelial cells, to induce antimicrobial proteins and resist intracellular viral growth to protect from viral infection; or on other immune cells, such as innate lymphoid cells (ILCs) that produce other cytokines that amplify the immune response.
the response to an initial infection occurs in three phases , what are these ?
These are the innate phase, the early induced innate response, and the adaptive immune response.
what do the first 2 phases rely on ?
The first two phases rely on the recognition of pathogens via pathogen-associated molecular patterns (PAMPs) by germline-encoded receptors of the innate immune system – pathogen recognition receptors (PRRs).
what does the adaptive immunity rely on ?
adaptive immunity uses variable antigen-specific receptors that are produced as a result of gene segment rearrangements.
why does adaptive immunity occur 96 hours after the infection ?
because the rare B cells and T cells specific for the invading pathogen must first undergo clonal expansion after recognition of the pathogen before they differentiate into effector cells that migrate to the site of infection and clear the infection. The effector mechanisms that remove the infectious agent are similar or identical in each phase.
what do most antimicrobial agents require to be done before they work ?
The innate immune system contains several proteins that are lethal for microorganisms. These are secreted by cells such as epithelial cells and phagocytic cells and are usually made as inactive proproteins that require a proteolytic step to complete their activation, whereupon they become capable of killing microbes by forming pores in the microbial cell membranes.
mucins ?
found in mucus that may prevent adhesion to epithelium by microorganisms to prevent receptor binding.
lysozyme
glycosidase (sugar cleaving enzyme) that attacks peptidoglycan in bacterial cell wall to degrade it.
defensins
disrupt cell membranes of bacteria and fungi via pore formation.
cathelicidns
disrupt cell membrane of wide range of microorganisms.
histatins
active against pathogenic fungi normally in the oral cavity.
RegIII family
C-type lectins which are sugar binding, which target peptidoglycans, promoting pore formation.
describe the structure of beta 1 defensins
It is composed of a short segment of an alpha helix (yellow) resting against three strands of antiparallel b sheet (green) generating an amphipathic peptide with charged and hydrophobic residues residing in separate regions.
what does this allow ?
allows the defensin to interact with the charged surface of the cell membrane and become inserted in the lipid bilayer (top right panel). A transition in the arrangement of the defensins in the membrane then leads to the formation of pores and a loss of membrane integrity (bottom right panel) in the bacterial cell wall.
there are over 30 different plasma proteins that make up the complement system , where are most of them produced ?
mainly the liver
describe complement activation ?
In the presence of pathogens (or antibodies bound to pathogens) the complement system becomes activated. Complement activation results in inflammation, phagocytosis and microbe destruction via membrane attack and pore formation. Activation follows interaction of complement proteins with soluble receptors (shown in red above) that recognize molecules/structures on microbial surfaces.
mannose binding lectin ?
recognise sugars, such as mannose; fructose which are expressed on the surface of a pathogen.
