Human Physio Immune System

Learning objectives

  • Identify components of the immune system and describe their functions
  • Describe the innate (nonspecific) and acquired (specific) immune responses
  • Distinguish the humoral and cell mediated immunity
  • Describe the various immune response pathways

Cells of the immune system

Basophils & Mast Cells (granulocytes)

  • releases chemicals that mediate inflammation and allergic responses

Neutrophils (granulocytes & phagocytes)

  • ingest and destroy invaders

Eosinophils (granulocytes & phagocytes)

  • destroy invaders, particularly antibody-coated parasites

Monocytes & Macrophages (agranulocytes & phagocytes)

  • ingest and destroy invaders
  • antigen presentation

Lymphocytes & Plasma cells (B cells, T cells, NK cells)

  • specific responses to invaders, including antibody production

Dendritic cells (Langerhans cells)

  • Recognise pathogens and activate other immune cells by antigen presentation

Lymphatic system

  • fluid leak out of capillaries onto tissue - lymph
  • lymphatic system returns fluid and proteins to circulatory system
  • picks up fat absorbed at intestines and transfers it to circulatory system
  • serve as filter for pathogens

Lymphoid tissues

  • Primary lymphoid tissues
    • Thymus gland
    • Bone marrow
  • Secondary lymphoid tissues
    • Encapsulated lymphoid tissues
    • spleen
    • lymph nodes
    • Diffuse lymphoid tissues
    • tonsils
    • gut associated lymphoid tissue
    • clusters of lymphoid tissues
Lymph nodes
  • filter lymph fluid before it has opportunity to enter back into blood vessels
  • collect antigens carried by lymph
    • engulfed by macrophages & presented to lymphocytes

Host defense

Innate immunity

  • non specific, immediate response
  • guided by granulocytes & macrophages
  • inflammation → reaction of cytokine mediated innate immunity

Acquired (adaptive) immunity

  • specific immune response directed at specific pathogen (antigen)
  • guided by lymphocytes and antigen presenting cells
  • <<cell mediated and humoral (antibody mediated) immunity<<

Mechanism of phagocytosis

  1. Microbe adheres to phagocyte
  2. Phagocyte forms pseudopods that eventually engulf the particle
  3. Phagocytic vesicle containing antigen (phagosome)
  4. Phagocytic vesicle is fused with a lysosome
  5. Microbe in fused vesicle is killed and digested by lysosomal enzymes within the phagolysosome, leaving a residual body
  6. Indigestible and residual material is removed by exocytosis

Inflammatory response (==innate immunity==)

Three important roles of inflammation:

  • attract immune cells and chemical mediators to the site
  • produce a physical barrier to retard the spread of infections
  • promote tissue repair once the infection is under control

Chemicals of ==innate== inflammatory response

Histamine from mast cells & basophils
  • swelling, edema, vasodilation
Interleukins
  • fever, blood vessels, more permeable to white blood cells and proteins, acute-phase proteins
Bradykinin
  • pain and swelling
Complement proteins
  • membrane attack complex

Acquired immunity/specific defenses

Adaptive immune system is a functional system that:

  • recognises specific foreign substances
  • acts to immoblise, neutralise, or destroy foreign substances
  • amplifies inflammatory response and activates complement
  • mediated primarily by lymphocytes
  • Adaptive immune system is ==antigen specific==, ==systemic==, and has ==memory==

Two mechanisms of action:

  • [[Humoral - (antibody) mediated (B cell) immunity[[
  • [[Cell mediated (T cell) immunity[[

Activated T lymphocytes develop into:

  • ∗∗HelperTcells∗∗−regulateotherimmunecells**Helper T cells** - regulate other immune cells
  • **Cytotoxic T cells** - attack & destroy virus infected cells (phagocytosis or chemical toxins)

Activated B lymphocytes develop into

  • ^^plasma cells - secrete antibodies^^

Cell-mediated (T cell) immune response

T cells bind to cells that display foreign antigen fragments as a part of ==major histocompatibility complex (MHC)==

  • MHC class I on ^^all nucleated human cells^^
    • recognised by ^^cytotoxic T cells^^
  • MHC class II on ==macrophages, B lymphocytes, and dendritic cells==
    • recognised by ==helper T cells==
Cytotoxic T cells
  • attack and destroy cells that ^^display MHC I antigen^^ complexes
  • release ^^pore forming perforins^^
  • release ^^granzymes^^ and ^^activates Fas to induce apoptosis^^
Helper T cells
  • secrete ==cytokines== that ==activate other immune cells==
  • ==bind to B cells== and ==promote their differentiation== into ==plasma cells and memory B cells==

Humoral-mediated (antibody/B cell response)

Mature B lymphocytes (B cells) insert antibody molecules into their cell membranes

  • Antibodies become %%surface receptors%% marking the members of each clone
When a clone responds to antigen, some %%effector cells differentiate into plasma cells%%
  • [[synthesise and secrete antibodies[[
A few %%memory cells remain behind%%, waiting to respond to the same antigen
  • soluble proteins secreted by activated B cells and plasma cells in response to an antigen
  • capable of binding specifically with antigen
  • 5 classes of antibodies: IgD, IgM, IgG, IgA, and, IgE

Acquired immunity

Naturally acquired

Active

Antigens enter the body ^^naturally^^; body produces antibodies and specialised lymphocytes (memory cells produced)

Passive

Antibodies pass from ^^mother to baby^^ via placenta or milk (no memory cells produced)

Artificially acquired

Active

Antigens introduced by ^^vaccines^^; body produces antibodies and specialised lymphocytes (memory cells produced)

Passive

Antibodies introduced through ^^immune serum^^ (no memory cells produced)