Pathology

1. BASIC IMMUNOLOGY , NATURAL AND ACQUIRED
IMMUNITY AND IMMUNITY RESPONSE
LECTURER TAMARA NWOKOLO

5. The immune system is a remarkable network of organs, cells, and
proteins that work together to protect our bodies from harmful
invaders.
Innate Immune System:
This is our first line of defense. It provides generalized
protection against a wide range of pathogens without prior exposure.
Components include:
Physical barriers: Skin, mucous membranes, and secretions.
Phagocytes: Cells (such as neutrophils and macrophages) that engulf
and destroy pathogens.
Natural killer (NK) cells: Detect and eliminate infected or abnormal
cells.
Complement system: A group of proteins that enhance immune
responses.
Inflammation: Triggered by tissue damage or infection, it recruits
immune cells to the site.The innate system acts swiftly but lacks
specificity.

7. DIFFERENCE BETWEEN INNATE AND ACQUIRED
IMMUNE RESPONSE.
Innate
 Depends on pre-formed cells and molecules
 Fast (starts in minutes/hrs)
 Limited specificity – pattern recognition of ‘danger signals
Acquired
 Depends on clonal selection: i.e. growth of cells or
antibodies, selected for antigen specificity.
 Slow (starts in days).
 Highly specific to foreign proteins

10. Nonspecific Immune Response (Innate Immunity)
 The nonspecific innate immune response provides a first line
of defense that can often prevent infections from gaining a
solid foothold in the body.
 These defenses are described as nonspecific because they do
not target any specific pathogen; rather, they defend against
a wide range of potential pathogens.
Physical Defenses:
 The skin acts as a physical barrier to keep pathogens out.
 Saliva, mucus, and tears protect openings in the skin (such as
the mouth and eyes) by containing enzymes that break down
bacterial cell walls.

14. System of
organ
Factor Mechanism
Mouth and
intestinal tract.
Saliva - lysosome & phospholipase
A
Low pH (HCL) – gastric juice
Bile salt
Alkaline pH (lower intestine)
Flushing action (intestine)
Mucous
Phospholipase A destroys
bacterial cell membrane.
Kills or inhibits microbes.
Prevents microbes.
Eliminates microbes which have
not succeeded to colonization
Urogenital tract Urine (acidity)
Flushing action (urine- vagina
secretions)
Acidic pH of vagina
Mantle of vagina
Low pH cleanses the urinary tract.
Inhibits growth of microbes.
Anatomical (physical) barriers- b) chemical factors
First line of host defense (surface defenses)

18. Adaptive Immune System:
• The adaptive immune system is more sophisticated and
specific. It adapts to recognize and respond to specific
pathogens.
Components include:
• B cells: Produce antibodies that target specific antigens.
• T cells: Coordinate immune responses and directly attack
infected cells.
• Antigens: Molecules (often proteins) on pathogens that
trigger immune responses.
• Memory cells: Remember previous encounters with
pathogens for faster responses.
• The adaptive system takes longer to activate but provides
long-lasting immunity.

19. Self vs. Non-Self Recognition:
 The immune system is able to distinguish between self
molecules (our own cells) and non-self
molecules (pathogens).
 Failure to recognize self can lead to autoimmune
diseases.Major Histocompatibility Complex.
 (MHC) molecules play a crucial role in this recognition.
Lymphatic System:
 The lymphatic system is intertwined with immunity.
 It includes lymph nodes, spleen, tonsils, and thymus.
 Lymph nodes filter lymph (a fluid containing immune cells)
and trap pathogens.
 The spleen removes old red blood cells and detects
infections.
 The thymus matures T cells.

21. Neuroimmune System:
 The neuroimmune system represents the connection
between the nervous and immune systems.
 Neurons release neurotransmitters that influence immune
responses.
 Stress, emotions, and circadian rhythms impact immune
function.
 The neuroimmune system also includes hormonal signals and
cytokines that participate in signaling between the immune
and nervous systems
 The key cellular components of the neuroimmune system
are glial cells, including astrocytes, microglia, and
oligodendrocytes.

23. Specific Immune Response (Adaptive Immunity)
When pathogens bypass innate immune defenses, the adaptive
immune system comes into play. This system is highly specific for
individual microbial pathogens.
 Antigens: These are molecules found on the surface of pathogens
and are unique to each pathogen.
 Lymphocytes: These specialized white blood cells play a crucial
role in the adaptive immune response.
 B cells: They produce specific antibodies to a particular pathogen.
 T cells: They assist B cells (helper T cells) and directly kill infected
cells (killer T cells).
Antigen-Specific Immune Response:
 Humoral Immunity: Mediated by B cells, which produce specific
antibodies against pathogens.
 Cell-Mediated Immunity: Involves cytotoxic T cells that induce the
lysis of infected cells.

24. Chemical Defenses:
 Inflammatory response: When a pathogen stimulates an
increase in blood flow to an infected area, blood vessels
expand, and white blood cells (phagocytes) invade the tissue
to engulf and destroy bacteria.
 Fever: The immune system may raise body temperature to
slow or stop pathogen growth and speed up the immune
response.

36. What triggers the innate immune response?
1. Triggers
 PAMPs – pathogen-associated molecular patterns e.g.
dsRNA in cytoplasm; bacterial cell wall components.
 DAMPs – danger-associated molecular patterns e.g.
monosodium urate; high extracellular [ATP]; reactive oxygen
species (ROS).
2. Pattern-recognition receptors Extracellular danger
signals.
 TLRs – Toll-like receptors Intracellular danger signals
 NLRs – NOD-like receptors
 RLRs - RIG-I-like receptors
 AIM2 - Absent in Melanoma 2..
 ADD FUNCTIONS.

37. Antigens
Molecules that react with antibodies or T cells.
Immunogens
Antigens that can initiate an immune response.
Antibody
They are immunoglobulin molecule in the blood and body fluids
which binds specifically to an antigen.
Immunoglobulins are proteins that act as antibodies, defending your
body from harmful invaders like bacteria and viruses.
They are made by white blood cells called plasma cells and circulate
in your blood and other fluids, such as urine and spinal fluid

38. Five classes of Immunoglobulins.
IgA
 Found in body secretions
 Contains a ‘secretory component’ which protects it from digestive
enzymes.
IgD
 Acts as an antigen receptor and antigen recognition on B cells by
regulating B cell function when it encounters antigen
IgE
 Involved in allergic response
 Binds to basophils and mast cells
 Triggers release of histamines.

39. IgG
 It is the most common and versatile type.
 Is the primary line of acquired defense against pathogens in
extracellular fluids (blood, lymph, and saliva).
IgM
 Important in primary immune response.
 It is the largest antibody and provides short-term
protection by clearing antigens from the bloodstream.
 It is also called a natural antibody and serves as the first line
of defense againt any new infection.

41. What is the normal function of the immune system?
• To identify and eliminate harmful microorganisms and harmful
substances such as toxins.
• By distinguishing ‘self ’ from ‘non-self’ proteins and
• By identifying ‘danger’ signals (e.g. from inflammation).
• The immune system must strike a balance between clearing
the pathogen and causing collateral damage to the host -
“immunopathology”.

42. How does the immune system cause disease?
• Immune deficiency persistent or fatal infections
• Allergy
• Autoimmune disease
• Transplant rejection.
HOW DOES AN ANTIBODY KILL A VIRUS?
Four important mechanisms:
1) Binds to virus and prevents attachment to cell.
2) Opsonization: virus-Ab complex is phagocytosed by MF.
3) Complement-mediated lysis of enveloped viruses.
4) Antibody-dependent cell-mediated cytotoxicity (ADCC),
mediated by natural killer (NK)-like cells

43. How does the immune response clear a pathogen?
 Cytotoxic T lymphocytes (CTLs) kill infected cells.
 Antibodies bind to pathogens: the complex is destroyed or
ingested by cells.
How does a T cell meet its antigen?
 Antigens are taken up by specialized antigen-presenting cells
and transported from the tissues into secondary lymphoid
organs, where they meet T cells.
What happens when the antigen is removed?
 Most lymphocytes that have proliferated recently will die after
fulfilling their function.
 Some survive as memory cells.

44. Vaccines:
 Vaccination provides acquired immunity by exposing the
immune system to harmless forms of pathogens,
allowing it to develop specific defenses.
 In summary, nonspecific defenses act as the first line of
protection, while specific immune responses are
the third line of defense and are triggered by antigens.
 Together, these systems work harmoniously to safeguard
our bodies against a wide array of threats.
 What is the second line of defense?.