The document provides an introduction to immunology and summarizes the three main types of immunity: 1. Barrier immunity: The skin acts as the first line of defense against pathogens through physical, chemical, and biological barriers. 2. Innate immunity: Nonspecific immunity present at birth that recruits immune cells, activates complement pathways, and identifies foreign substances to activate adaptive immunity. 3. Adaptive immunity: Highly specific immunity that develops after exposure to pathogens through lymphocytes. It provides long-lasting protection by distinguishing foreign from self but can also cause autoimmune diseases if it attacks the host's own molecules.

1. Introduction to Immunology
Dr. Imran Khan
Department of Biotechnology
Abdul Wali Khan University Mardan, KPK
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2. • Immunology: The study of Immune system
• Immune system: It’s the body defense
system against foreign entities such as
pathogens, antigens.
• In short, it remove everything from body
which should not be in the body. It can also
remove damaged or malignant cells
What are pathogens?
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3. Pathogens are organisms (mostly microorganisms) that can cause
disease.
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4. Types of immunity
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1. Barrier immunity:
Taking skin as an example:
• Skin is the outermost layer of the body with an extensive surface area of approximately 1·8 m2
• It is the first line of defense against a multitude of external pathogens and environmental insults
• The skin also has important homeostatic functions such as reducing water loss and contributing to
thermoregulation of the body

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Physical barrier
Chemical barriers
(antimicrobial proteins)
Biological barriers
(Immune cells)
1. Barrier immunity:

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9. 2. Innate Immunity: Innate, or nonspecific, immunity is the
defense system with which you were born
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10. Major function of innate immunity
• recruit immune cells to infection sites by producing chemical factors, including
chemical mediators called cytokines
• activate the complement cascade to identify bacteria, activate cells, and promote
clearance of antibody complexes or dead cells
• identify and remove foreign substances present in organs, tissues, blood
and lymph, by specialized white blood cells
• activate the adaptive immune system through antigen presentation
• act as a physical and chemical barrier to infectious agents; via physical measures
such as skin and chemical measures such as clotting factors in blood
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11. 3. Adaptive immunity
• A type of immunity that develops when a person's immune system responds to a foreign substance or
microorganism, such as after an infection or vaccination.
• The function of adaptive immune responses is to destroy invading pathogens and any toxic molecules they
produce.
• The ability to distinguish what is foreign from what is self in this way is a fundamental feature of the adaptive
immune system.
• Unlike innate immune responses, the adaptive responses are highly specific to the particular pathogen that
induced them.
• They can also provide long-lasting protection.
• Any substance capable of eliciting an adaptive immune response is referred to as an antigen (antibody
generator) 11

12. 3. Adaptive immunity
• If the system fails to make this distinction and reacts destructively against
the host's own molecules. Such autoimmune diseases can be fatal.
• Allergic conditions such as hayfever and asthma are examples of
deleterious adaptive immune responses against apparently harmless
foreign molecules.
• Such inappropriate responses are normally avoided because the innate
immune system calls adaptive immune responses into play only when it
recognizes molecules characteristic of invading pathogens called pathogen-
associated immunostimulants
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Adaptive immune responses are carried out by
white blood cells called lymphocytes

14. Brief comparison between innate and
adaptive immunity
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