Lecture 2 Immunity
• Key features of immune system are specificity and memory
• Distinguish self and non-self
• 3 major functions
1) Protects body from disease causing invaders known as pathogens (bacteria, virus, fungi, protozoans,
multicellular parasites). Substances that trigger the body’s immune response and can react with
products of that response are known as antigens
2) Removes dead or damaged cells
3) Recognize and remove abnormal cells
• 3 categories of immune pathologies
1) Incorrect response (autoimmune)
2) Overactive response (allergies)
3) Lack of response (immunodeficiency disease)
Pathogens of the Human Body
Bacteria and Viruses Require Different Defense Mechanisms
• Bacteria and Virus Difference in many ways, so body need different immune response
Structure Cells. Usually surrounded by cell Not Cells. Consists of nucleic
wall. Some encapsulated acid core with capsid (protein
bacteria has capsule (protective coat). Some have an envelope of
layer) phospholipid and protein
Living Conditions and Repro Most can survive and reproduce Parasitic. Must use host cell to
outside host if they have required replicate and reproduce.
nutrients, temp, pH etc.
Susceptibility to Drugs Most can be killed by antbiotics Cant be killed by antibiotics. Can
be inhibited by antiviral drugs that
target their replication
Virus Can Replicate Only Inside Host Cells
• Virus binds to membrane receptors, trigger endocytosis.
• Inside, virus nucleic acid takes over the host cells resources to make new viral nucleic acid and proteins.
They then form the mature virus and lyses.
• Viruses are released 1) by rupture the host cell 2)bud off
• They disrupt cell’s metabolism , others incorporate DNA into host cell DNA (oncogenic viruses) can cause
The Immune Response
• The body has 2 lines of defense. Physical and chemical barriers to keep pathogens out of body
• Then the 2 line is the immune response
• Steps of immune response: 1) detection and indentification 2)communication with other immune cells to
make organized response 3) recruit assistance and coordinate response among participants
4) destruction and suppression
• Not all can be destroyed but can control damage and keep invaders from spreading.
• Detection, identification, communication, recruitment, coordination and attack all depend on signal
molecules such as antibodies and cytokines. • Antibodies: proteins made by immune cells that bind antigens and make them more visible to immune
• Cytokines: protein messengers made by one cell that affect the growth or activity of another cell
• 2 categories of human immune response:
1) Nonspecific innate immunity (present at birth)
Immune cell receptors have broad specificity for innate immunity and respond to many molecular
signals that are both unique and common to pathogens. Begins rapid. Inflammation is the hallmark
2) Specific Acquired Immunity
The receptors are very specific and distinguish between different pathogens
Slow and take long time to react. React more rapidly with more exposures
i) Cell mediated immunity: use contact dependent signaling in which immune cell receptor
binds to a receptor on its target cell
ii) Humoral Immunity: antibody mediated, uses antibody to carry out immune response
The innate response is the more rapid one and is reinforced by the slow antigen-specific acquired response,
which amplifies the efficacy of innate response.
Anatomy of the Immune System
Lymphoid Tissues Are Everywhere
• The immune system has 2 anatomical components: lymphoid tissues and the cells responsible for the
• 2 Primary lymphoid tissues: thymus gland and bone marrow
• Some mature immune cells don’t specialize till they expose to pathogen.
• Secondary lymphoid tissues have mature immune cells that interact with pathogens and initiate response.
Divided into encapsulated and unencapsulated diffuse lymphoid tissues.
• Encapsulated lymphoid: spleen and lymph nodes
Both have outer wall formed from fibrous collagenous capsules.
Spleen has immune cells used to monitor blood for foreign invaders
Lymph nodes are associated with lymphatic circulation. The filtered fluid out of the capillaries is
picked up by lymph capillaries and passes through encapsulated lymph nodes on its journey back to
Immune cell in the nodes intercepts the pathogens using breaks in the skin or mucous, once inside,
the cells prevent pathogens from spreading
• The Unencapsulated diffuse lymphoid tissues are aggregation of immune cells that are in other organs.
Include tonsils and gut-associated lymphoid tissue (GALT), which lies under the epithelium of
esophagus and intestines
Also lymphoid tissues associated with the skin, respiratory, urinary and reproductive tract.
The immune cells intercept pathogens before they get into the circulation.
GALT is the largest immune organ
Immune cells are concentrate at area that are likely to encounter antigens