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Human Phys

The immune system

QuestionAnswer
Immune system function Comprises group of cells, molecules, and organs that act together to defend the body against “foreign” invaders that may cause disease (e.g. bacteria, viruses, fungi) - Remarkably versatile defence system
Why did it evolve? - to protect animals from invading pathogenic microorganisms (viruses, bacteria, fungi), parasitic organisms and cancer
Able to generate enormous variety of cells and molecules capable of specifically recognising and eliminating endless variety of foreign invaders; “good” non-self vs “bad” non-self
RECOGNITION and RESPONSE (effector and memory) INNATE and ADAPTIVE (or ACQUIRED) immunity HUMORAL and CELLULAR responses
Innate immune system - Rapid response – Low specificity – Limited diversity – No memory – Physical and chemical barrier – Blood protein (cytokines, Complement) – Cells (phagocytes, NK)
Adaptive (specific) – Slow response – High specificity – Large diversity – Memory – Blood protein (cytokines, Antibodies) – Cells (Lymphocytes, APC)
Innate immune system - mostly present before infection; not specific to pathogen - anatomic barriers: skin, mucous membranes - physiologic barriers temperature, low pH, chemical mediators (lysozyme, interferon, complement)
- phagocytic/endocytic barriers monocytes, neutrophils, macrophages - inflammatory barriers
Antigen presenting cells (APC) Activation of immune system requires cytokines produced by TH cells, which in turn require APCs APCs display antigen with MHC II molecules to TH cells macrophages B lymphocytes dendritic cells
How do they work? take up Ag by phagocytosis break into peptides display bound to MHC II interaction with TCR of TH cell co-stimulatory signal
Neutrophils - type of wbc
Neutrophil processes NETosis: cell throws out DNA in a net to catch pathogens Degranulation: toxic granule proteins released Phagocytosis
Effects of complement - lysis - osponization - inflammatory response - immune complexes
T cells (lymphocytes) mature in thymus (originate in bone marrow) unique antigen binding molecule T cell receptor (TCR) recognises Ag bound to MHC molecules (major histocompatibility complex)
T cells TH (T helper) and TC (T cytotoxic) subpopulations also Treg (regulatory)
T cells encounter antigen with MHC (TH with antigen-MHCII, TC with antigen-MHCI): rapid division differentiation memory T cells various effector T cells
Antigen Recognition by B and T lymphocytes T cell - MHC binds to APC MHC= major histocompatibility complex
B cells (lymphocytes) mature in bone marrow unique antigen-binding receptor membrane bound antibody molecule encounter antigen matching Ab: rapid division differentiation memory B cells plasma cells that secrete Ab
Immunoglobulins antigen binding proteins present on B cell membrane confers antigenic specificity secreted by plasma cells effectors of humoral immunity: search out and neutralise antigens mark antigens for elimination
Basic structure Antibody molecules have a common structure of four peptide chains: two identical light chains k, l two identical heavy chains m, g, a, d, e (isotypes) IgM, IgG (g1, g2, g3, g4), IgA (a1, a2), IgD, IgE resp.
Basic structure 2 identical light chains and 2 identical heavy chains ~25,000 x2 ~50,000 x2 total: ~150,000daltons/subunit disulphide bonds join Light-Heavy, Heavy-Heavy number and position of S-S bonds varies also non-covalent interactions
Immunoglobulin-mediated effector functions Opsonization Promotion of phagocytosis by macrophages (mf) and neutrophils FcR (Fc receptors) bind C region of most IgG subclasses Binding of FcR to Fc-Ag triggers phagocytosis
Antibody dependent cell mediated cytotoxicity (ADCC) Ab bound to target cells (virus infected) with Fc receptors of NK cells directs cytotoxic activity apoptosis not phagocytosis
Activation of complement IgM and IgG activate series of serum glycoproteins lysis of bacterial cell by perforation of membranes
Created by: reub8n
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