BM108 Block C

Pathogen (definition)

Organism that can produce disease (aka germs or infectious agents)

Virion (size)

small, 10-400nm

Obligate parasite (definition)

Needs a host to complete life-cycle or reproduce

Virus (structure)

Nucleic acid genome core, protein caspid (protects genome), phospholipid envelope with spike projections

Caspid (function)

A coat that protects the genome

Spike proteins (function)

Allows virus to attach to target cell surface

Virus life cycle (6 steps)

Attaches, enters by endocytosis, uncoats, replicates, assembles new virions, progeny leaves

Measles (general info)

Virion around 100nm in diameter, highly contagious respiratory virus.

Measles (lifecycle)

Starts in lymph nodes, 4-7 days infects liver, epithelium, monocytes, etc. After 10 days cold like symptoms. 14-16 days general rash. 19-23 days infection cleared

Bacteria (definition)

Unicellular prokaryotes with no nucleus, size ranges between 500nm-2um. Has a rigid cell wall to maintain shape

Bacteria (shapes)

Spherical, rod, spiral

Extracellular pathogenic bacteria

Multiply in the host but on surfaces and in cavities (e.g. staphylococcus aureus) Uses virulence mechanisms to evade immune system

Intracellular pathogenic bacteria

Invades host cells to multiply (e.g. salmonella enterica)

Tuberculosis (definition)

Caused by mycobacterium tuberculosis spread by coughing and sneezing. Intra-macrophage therefore can spread to kidney spine and brain.

Tuberculosis (treatment)

antibiotics, 6-9 month treatments but long and expensive. Prevented by the BCG vaccine (70-80% effective)

Pulmonary tuberculosis (symptoms)

Attacks lung first, 2 weeks post infection night sweats, persistent fever, and weight loss

Fungi (definition)

Eukaryotic, 3-15um in length and 2-8um diameter

Fungi (3 basic cell types)

Spore, hyphae, yeast

Fungi (structure)

Nucleus, organelles, chitin cell wall

Fungal infections

Infect endothelial or epithelial cells intracellularly (induced endocytosis or active), spores germinate to produce a mycelium

Candidiasis (mechanisms)

Enters mucosal surface, abundant on surface of skins - infection happens for immunosuppressed people (e.g. HIV, cancer). Exists mainly as yeast as a part of a biofilm but can switch between yeast and filamentous forms.

Systemic Candidiasis

Fungus enters via mucosal surface, untreated has 30-50% mortality rate. Macronodular skin lesions, inflamed eye, occasionally septic shock. Treated by antifungal medicines.

Protozoa (definition)

Eukaryotic organisms between 1-30um, can be intracellular (can invade) or extracellular (reside on surface).

protazoa (infection)

Varies between; insects (ticks, mosquitos), contaminated food or water, or sexually transmitted. Infection caused when immune system cannot control parasite

Malaria

Infection initiated by mosquito, plasmodium sporozoites migrate to liver replicating tens of thousands of daughter cells. Merozoites released invading RBCs

Extracellular parasites (overview)

Too big for cells to kill (up to 15m in tapeworms), infection through different routes; ingestion of larvae, larvae eggs, skin contact, or mosquito bite

Ascaris (overview)

Extracellular parasite, 576-740 million people infected, cause anemia in 10% cases, impair the physical and intellectual development in children

Ascariasis (lifecycle)

Ingest eggs (human faeces, or uncooked food contaminated), eggs hatched in intestine, larvae gets through intestinal wall and travels through bloodstream. Gets coughed up then swallowed into intestine

Ascariasis (symptoms)

Diarrhoea, blood in faeces, passing a worm, stomach pain, nausea, vomiting, weight loss

Two arms of the immune response

Innate immunity, adaptive/acquired immunity

Innate immunity (summary)

First responders, no lasting immunity, not specific

Adaptive/acquired immunity (summary)

Developed during a lifetime, immunological memory, very specific

Innate immunity (first responders)

Innate immune cells are almost always immediately available and first to arrive to site of infection

Innate immunity (non-specific)

Protects against foreign cells or entities without having to recognise their specific identity. Recognises a general, conserved region of a cell or pathogen that marks the invader as foreign

Innate immunity (mucus)

Sticky to trap invaders but also has antimicrobial properties

Innate immunity (stomach acid)

Destroys invaders

Innate immunity (skin glands)

Secrete antimicrobial molecules such mild acids and enzymes

Innate immune cells (subtypes)

Granulocyte and monocyte

Phagocytic cells

Majority of innate immune cells

Phagocytosis (definition)

The process of engulfing and destroying pathogens by endocytosis

Neutrophil (overview)

Normally first cell type to arrive. Phagocytose and kill bacteria; mediate inflammation

Monocyte (overview)

Develop into macrophages or dendritic cells

Macrophage (overview)

Phagocytose microbes; mediate inflammation; present antigens to adaptive immune cells (T cells)

Dendritic cells (overview)

Properties like macrophages - main antigen presenting cell.

Basophil (overview)

Enter tissues at site of injury and secrete heparin (anti-clotting factor) and histamine

Eosinophil (overview)

Phagocytose and release chemicals that will kill parasites. Participate in allergic responses

Mast cells (overview)

Secrete histamine in inflammatory response; participate in allergic response

Natural killer cells (overview)

Attack general features cancerous and virus infected cells; also part of specific immunity

Inflammation (overview)

Innate response, allows elimination of foreign invaders. Clears area of dead cells and sets stage for tissue response

Inflammation (key cells)

Phagocytes including neutrophils, macrophages, dendritic cells, and mast cells. Induced and regulated by cytokines.

Inflammation - Stage one

Splinter causes an injury and introduces bacteria. Inflammatory signals produced by injured cells; histamine, neutrophils, endothelial cells.

Inflammation - Stage two

Capillaries dilate and become leaky. Increased blood flow to area increases delivery of beneficial proteins, increased vascular permeability allows plasma proteins to enter interstitial fluid. Fluid and neutrophils exit the capillaries and enter the site of the wound

Inflammation - Stage three

Phagocytes encounter microbes releasing inflammatory mediators (e.g. cytokines) that bring more phagocytes. Neutrophils and macrophages engulf and destroy bacteria. Capillaries return to normal, infection is controlled.

Pathogen Associated Molecular Patterns (PAMPs)

Innate immunity depends on these to recognise features common to many types of pathogens. Conserved molecular features vital to the survival of pathogens

Toll-like Receptors (TLRs)

Accomplish recognition on membranes of immune cells (e.g. macrophages and dendritic cells). Recognise and bind to pathogens with PAMPs

Adaptive immunity (CD4 T Cells)

Lymphocyte that assists in activating cells. Cell-mediated immunity

Adaptive immunity (Cytotoxic CD8 T cells)

Directly kill infected cells. Cell-mediated immunity

Adaptive immunity (humoral immunity)

B cells turn into plasma cells that secrete antibodies

Adaptive immunity (NK cells)

Similar to T cells but also perform non-specific actions

Adaptive immunity (lymphatic system)

network of vessels and organs with circulating lymphocytes

Primary lymphatic organs

Where B and T cells mature; bone marrow (B cells), Thymus (T cells)

Secondary lymphatic organs

Where lymphocytes activate and replicate