LYMPHOID SYSTEM

• skin and mucous membranes (mucosae)

  • act as physical barriers to the entry of harmful substances into the body
  • skin
  • impenetrable to most microorganisms unless injured
  • mucosae
  • easier to breach physically
  • a variety of structural and physiologic factors help them in preventing the entry of harmful microorganisms and substances
  • mucus
  • cilia
  • tears
  • saliva
• mucus

  • protects the mucosal surfaces of the respiratory, digestive, and genitourinary tracts
• cilia

  • help move and eliminate toxic substances
• tears and saliva

  • contain antibacterial substances including lysozymes that fight off pathogenic microorganism
• inflammatory response and immune response

  • When its first line of defense fails the body unleashes an army consisting of a staggering number of cell called
• INFLAMMATORY RESPONSE (NON-IMMUNE RESPONSE; INFLAMMATION)

  • immediate but mainly localized process
  • starts within minutes of tissue damage
  • effector cells assisted in carrying out the process by a host of other cells
  • destroy invading organisms and foreign antigens by phagocytosis or by releasing substances
  • release chemical mediators that attract or facilitate the entry of phagocytes and other cell
  • foreign organisms or substances are detected by the complement system
• Effector cells

  • phagocytes
  • neutrophils
  • macrophages
• assists effector cells

  • eosinophils
  • basophils
  • mast cells
  • NK cells
  • T cells
• chemotaxin

  • chemicals that attract phagocytes
  • produced to betray microorganisms
• complement system

  • collection of more than 20 plasma proteins that are produced by the liver (sequentially activated)
  • immune - activated by, and complements the work of, the antibodies (immunoglobulins)
  • inflammation - spontaneously activated in the presence of microorganisms or other foreign substances
• activate in the complement system during inflammation:

  • opsonins
  • facilitate phagocytosis
  • cytokines
  • act as signaling compound
  • histamine
  • released by the other mediators of inflammation by mast cells and basophils
  • activated phagocytes
  • congregate in the injured area
  • engulf and digest the invading microorganisms or other foreign elements
  • cytokines
  • further attract and activate other cells
  • T-cells
  • first step in immune response
• cytokines

  • responsible for the classical local signs and symptoms of inflammation (i.e., swelling, redness, heat and pain)
  • contribute to, the systemic signs and symptoms (fever)
• fever

  • occurs when interleukin-1, a cytokine produced by activated macrophages enters the bloodstream
  • reaches the hypothalamus, the temperature-regulating center in the brain
  • hypothalamus then responds by increasing body temperature
• IMMUNE RESPONSE (IMMUNOLOGICAL RESPONSE)

  • more powerful body defense system
  • new - it takes longer time
  • must be developed
  • antigen-specific
• lymphocytes

  • principal effector cells of the immune response
  • aided in carrying out the process by a variety of cell
  • two trillion in the body
  • 1% of body weight
  • capable of conferring immunity against as many as 10^11 different antigen
  • possess other surface markers or receptors
• B-cells

  • B-cell antigen receptors (BCR)
• T-cells

  • carry T-ceII antigen receptors (TCR)
  • express the CD3 molecular complex
• CD3 molecular complex

  • responsible for signal transmission and mediated via the T-cell receptor (TCR)
• NK cells

  • carry natural cytotoxicity receptors (NCR)
  • are also CD3-positive
• CD4 markets (CD4+ T-cells)

  • can differentiate into helper T-celIs (Th cells)
• CD8 markers (CD8+. T-cells)

  • can differentiate into cytotoxic T-celIs (Tc celIs) and suppressor T-celIs (Ts celIs)
• Types of Immune Responses

  • humoral (humoral immunity)
  • cell-mediated (cell-mediated immunity)
• Humoral Immunity (Antibody mediated immunity; AMI)

  • mediated by antibodies
  • important in containing many viral and bacterial infection
  • type of immunity that is conferred by vaccines against many childhood illnesses
• Antibodies

  • do not destroy antigen
  • simply bind to the antigens
  • able to neutralize or help eliminate the antigens
  • prevent the pathogen from invading the cells
  • immobilize bacteria and protozoans
  • serve to pinpoint antigens to phagocytes such as neutrophils and macrophages
• phagocytose

  • facilitated by the participation of the complement system.
• Cell-mediated Immunity (CMI)

  • mediated by antibodies
  • primarily the function of T-cells
  • effector cells
  • cytotoxic T-cells
  • responsible for delayed hypersensitivity reaction and tissue and organ transplant rejection
• cytotoxic T-cells

  • eliminate antigens that are inside cell
  • protect cells from antibodies
  • target cells (virus- infected cells & cells with intracellular bacteria)
  • destroy the cells that harbor the microorganisms
  • target cancer cells and cells that are foreign to the body
  • destroy target cell by inducing apoptosis
  • release the proteins in their cytoplasmic granules into the area where their target cells are
• primary immune response

  • entry of a new antigen
• secondary immune response

  • Subsequent entries of the same antigen
• Primary Immune Response

  • eliminate the new antigen
  • produce a population of lymphocytes (i.e., memory B-cells and memory T-cells) that retain the image of the new antigen
  • long induction phase time (days to weeks)
  • multi-stage process
  • steps:

  1. antigen recognition
  2. lymphocyte activation
  3. effector phase
• Antigen Recognition

  • new antigen that has penetrated surface epithelium
  • immediately encounters an antigen-presenting cell (APC)
• Antigen-presenting cell

  • cells that phagocytose
  • destroy and process antigens
  • display fragments of the antigen on their surface for presentation to naive CD4+ T-cell
• naive CD4+ T cells

  • mature cells that have been released by the bone marrow and which have not encountered an antigen yet
  • do not differentiate into Th cells unless they are presented an antigen by an APC
• naive B-cells

  • do not react to an antigen unless they are activated by cytokines produced by helper T-cells (Th cells)
• Naive CD8+ T-cells

  • do not differentiate into T cells unless c they are activated by APCs or helper T-cells
• endothelial cells and NK cells

  • can present antigens to T-cell
• "professional" APCs

  • cells can deliver the two signals (antigen signal and co-stimulatory signal) that are needed by naive CD4+ T-cells to get activated
  • macrophages
  • dendritic cells
  • B-cells
• Macrophages

  • effector cells of the inflammatory response
  • engulf antigens by phagocytosis
  • do not simply destroy the antigens with their lysosome
  • process the antigens and attach fragments of the antigens on their surface for presentation to naive T-cells
• Dendritic cells (DCs)

  • derive their name from the branched projections (dendrites) they exhibit as mature cells
  • most potent of the APCs
  • limited capacity for phagocytosis, just enough to enable them to process antigens and then attach antigen materials on their surfaces for presentation to naive CD4+ T-cells
• 2 broad categories of dendritic cells:

  • myeloid-related dendritic cell (mDC)
  • lymphoid-related dendritic cell (plasmacytoid dendritic cell; pDC)