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Innate Immunity
Present before exposure to pathogens
Present at birth
Non-antigen specific
Consists of:
– Skin… barrier for microbes and viruses
• Compromised by abrasion or laceration
• Sebacious sweat is acidic (pH 3-5)… prevents colonization of bacteria
– Mucus membranes… secrete mucus to trap microbes
• Mucocilliary escalator moves trapped microbes out of the trachea
• Secretions contain lysozyme, an enzyme, to digest the walls of
bacteria
– Phagocytic cells
Innate Immunity
• Mediate inflammation to limit the spread of microbes
• Contain antimicrobial proteins that bind to the surface of bacteria
• Once engulfed the phagocyte fuses a lysosome to the vacuole
containing the bacteria
• Some bacteria evade phagocytes by hiding surface recognition via a
capsule
• Types:
– Neutorphils… 60-70% of all WBCs
» Attracted to infection
» Sacrifice themselves after phagocytosis
– Macrophages… ~5% (developed from monocytes)
» Attack microbes trapped in the lymph system and various other organs
– Eosinophils… active against multicellular invaders
» Inject enzymes to damage organism
– Dendritic cells… stimulate acquired immunity after ingestion of cells
Innate Immunity
• The compliment system consists of over 30 proteins that
when activated attack organisms and activate the immune
system
– Initiated be lysozyme
– Interferon… limits viral replication in cells neighboring an
infected cell
• Non-specific
• Inflammatory response… due to injury of pathogens
– Created by histamine release from mast cells in the epithelium
• Cause swelling of capillaries and increased blood flow that leaks fluid
into tissues bringing macrophages
– Discharge of prostaglandins that further promotes blood flow
– Release chemokines that direct phagocytes to the infected area
Innate Immunity
• Natural Killer Cells
– Patrol the body looking for infected cells.
• They attack and cause cell death through apoptosis
• Evaded in some viral infections and cancer
Acquired Immunity
• Often called adaptive immunity
• Developed only after exposure
• Highly specific
• Lymphocytes… key cells in acquired immunity
– Activated by the presence of cytokines
– Antigens (foreign particles) elicit the immune
response
• Epitote… small part of the antigen molecule that is
recognized by a specific lymphocyte
– Each lymphocyte may contain up to 100,000 identical epitote
recognition sites
• Activation causes immediate clonal response producing 2
additional cells… 1 being a memory cell
– Called the primary immune response
» Maximum response 10-17 days after initial exposure
• Sickness ensues awaiting max immune response
Acquired Immunity
– B-lymphocytes… recognize and bind to intact surface antigens
• Developed in the bone marrow from pluripotent cells
• Secrete antibodies
» Bind to antigens to mark for elimination
» Shorten subsequent infections
• Called the secondary immune response
Acquired Immunity
– T-lymphocytes… similar to B-lymphocytes but can
bind to smaller epitotes called MCH molecules
• Originate in the bone marrow but mature in the thymus
gland
• Class 1 MCH… found on almost every cell in the body
– Are presented when the cell becomes infected signaling the
cytotoxic (killer) T-cells
• Class 2 MCH… presented by macrophages, dendritic
cells, and B-cells through antigen-presenting.
– Signals the helper T-cells