Immune System Flashcards
What is immune system
Body’s ability to resist or eliminate potentially harmful foreign materials (pathogens)
Types of pathogen
Virus bacteria parasite fungi Protozoa
Types of immunity
Acquired immunity and innate immunity
External barriers
Skin and mucus
Fluids eg sweat saliva (lysozymes)
Stomach (digestive enzymes and gastric acid)
Innate immunity
Always ready to attack. Many pathogenic microbes have evolved to resist innate immunity
Non specific- cannot distinguish between pathogens
Fast and immediate
No memory
Cells of innate immunity
Phagocytes, dentritic cells, NK cells and complements
Adaptive immunity
stimulated by exposure to microbe, more potent
Highly specific- distinguishes using shapes on surface called antigens
Slower
Immunological memory
Cells of adaptive immunity
B lymphocytes and T lymphocytes
Types of innate immunity
Cellular - phagocytes, eosinophils, basophils, chemical- cytokines
Phagocytes are
Cells that track down, engulf and destroy bacteria, other pathogens and our own damaged and dead cells
Types of phagocytes
Neutrophils (most abundant) monocytes/ macrophages
Neutrophils work how
Contain destructive enzymes such as peroxidases, alkaline and acid phosphates which kill and destroy bacteria and other pathogens
Monocytes work how
Larger than neutrophils so can engulf bigger pathogens. Break down pathogens and process the antigens then present these antigens to the cells of the adaptive immunity to produce specific immune response
APCs (antigen presenting cells)
How does the process Phagocytosis go
Microbes attach to phagocyte surface, endocytosis of microbe and formation of phagosome, fusion of phagosome and lysosome, killing of microbe through digestion by enzyme, discharge of waste
Lysozyme
Digests bacterial cell wall
Eosinophils do what
Help combat parasitic infections, involved in allergy and asthma, contain enzymes
How do u experience an allergic reaction or asthma attack
The body reacting to histamine which is released by mast cell which is activated by allergen. Histamine targets receptors on a specific tissue and trigger a specific reaction eg itchiness in the skin
Basophils
Least common white blood cells, contain large cytoplasmic granules with inflammatory mediators, no proven function, found in parasitic infections
Cytokines are
Small proteins secreted by cells in response to stimulus. Trigger biological responses when they bind to specific receptors
Where are lymphocytes produced
Bone marrow
Lymphatic system does what
Transport of white blood cells. Drainage of tissues, absorption and transport of fatty acids and fat, immunity
lymphatic organs primary and secondary
Bone marrow and thymus
Lymph nodes and spleen and tonsils
What happens in primary lymphoid organs
Where blood cells are produced (hematopoiesis in bone marrow) and B cells receive this early training- acquire ability to interact with antigens
What happens in thymus
T cells are educated. In cortex they are mature, medulla they are immature
What do lymph nodes do
Induce adaptive immune responses to antigens carried from the tissues by lymph
3 phases of immune defence
Recognition of danger, production of specific weapons, transport of weapons to site of attack
Spleen
Acts as a filter for blood by recycling old RBCs and platelets and white blood cells are stored there
What are T lymphocytes responsible for
Cell mediated immunity and assisting B cells
Types of t lymphocytes
Cytotoxic T cells (CD8+) and Helper T cells (CD4+)
Cytotoxic T cells function and when does it recognise antigens
Kill cells When they’re bound to MHC I
Helper T cells function and when does it recognise antigens
Stimulate B cells to produce antibody. Cannot kill pathogens but can activate and direct other cells. bound to MHC II
What does perforin do
Creates holes in infected cell where enzymes that promote apoptosis can enter
What is MHC I
Self-nonself complex that is responsible for the presentation of an antigen on the pathogen. Found on virtually all nucleated cells. Endogenous pathway. Presents antigen to CD8+ cells
Classes of TH cell and their target cell
TH1 - macrophages
TH2 - eosinophils
TH17- neutrophils
TfH- B cells
What is MHC II
Found only on professional antigen presenting cells ie macrophages. Presents exogenously produced antigen to CD4+ T cells
What do B cells do
Produce antibodies directed against antigens. They express B cell receptors BCRs and on activation they are differentiated into plasma cells with the help of T helper cells. Also produce memory B cells
What are antigens
Small proteins on the surface of a pathogen that are recognised by antibodies
Two regions of antibody
Antigen binding region- upper region and the part that recognises antigens
Fc region- lower region solid and stable part that attaches to surface of B cell (has disulphides bonds)
Types of antibody (5)
IgM- first class to be produced, less specificity IgA- protects mucosal surfaces IgE- defends against parasites and causes allergies IgD- unknown function IgG- main type
Functions of antibodies
Neutralisation- prevention of attachment and entry of cell free viruses (mostly IgA)
opsonisation- helps direct macrophages towards certain pathogens by adding lots of antibodies to the pathogens
complement activation
Complement system
Consists of more than 30 proteins/ factors that are found in plasma, in an inactive form. Activated in a cascade like format.
Types of pathway of complement system
Alternative, classical, lectin
What is the result of complement system and what effect does it have on microbes
Membrane attack complex MAC
Creates a cytotoxic pore and liquid leaks out, killing the cell
Functions of complement system
Direct lysis of target cells, recruit other immune cells to the site of infection to enhance the immune response, produce things that enhance phagocytosis
Passive immunity
Transfer of antibodies or lymphocytes specific for the microbe
B memory cells are not present and it is a short lived solution
Active immunity
Protective immunity against a pathogen may be induced through the hosts own response to that pathogen
B memory cells are made and this is a long term or permanent solution
