This document provides an introduction to immunology, outlining key concepts. It defines immunity, describes the functions of the immune system in preventing infection and maintaining homeostasis. It distinguishes between innate and acquired immunity, describing their unique characteristics. Key cells of the immune system are briefly discussed.

1. ZERA INTERNATIONAL COLLEGE
OF HEALTH SCIENCES
DEPARTMENT OF CLINICAL MEDICINE
IMMUNOLOGY
LECTURE 1: INTRODUCTION TO IMMUNOLOGY
Mrs Natasha N Ng’andwe
BSc, BMS

2. Lecture Outline
 Define immunity
 Functions of the immune system
 Concepts in immunology
 Unique characteristics of immune responses
 Comparison between innate & acquired immunity
 Briefly look at cells of the immune system

3. Introduction
 The term immunity, derived from the Latin “immunis” (exempt), was adopted to designate this naturally
acquired protection against diseases such as measles or smallpox.
 Immunology can be described as a branch of biology that covers the study of immune systems in
organisms
 The emergence of immunology as a discipline was closely tied to the development of microbiology.
 The work of Pasteur, Koch, Metchnikoff, and many other pioneers of the golden age of microbiology
resulted in the rapid identification of new infectious agents, closely followed by the discovery that
infectious diseases could be prevented by exposure to killed or attenuated organisms, or to compounds
extracted from the infectious agents.

4. Functions of the immune system
 Prevent or limit invasion by microorganisms.
 Eliminate micro-organisms in the body.
 Maintain homeostasis both external & internal body environment

5. General concepts in immunology
1. Innate (non specific) & acquired (specific) immunity.
 Innate immunity (non specific) are defenses that we are born with or are present
from the time we are bone.
 Acquired immunity ( specific) are defenses that are induced during the life of the
individual as part of the complex sequence of events designated as the immune
response.

6. HOST RESPONSE TO MICROBIAL WORLD

7. LINES OF DEFENSE
FIRST LINE : ANATOMICAL BARRIERS
 Mechanical barriers (skin & mucous membranes)
 Chemical barriers (acid and antibacterial peptides)
 Physiological barriers (temperature, pH)
SECOND LINE : innate immune cells
 Phagocytes (monocytes/macrophages, neutrophils and dendritic cells)
 Natural killer cells (NKCs)
 Inflammatory cells (mast cells, basophils, eosinophils)

8. LINES OF DEFENSE
THIRD LINE: adaptive immune cells
 Lymphocytes (T cells and B cells)
 Humoral immunity: Immunoglobulins (antibodies)
 Cell-mediated immunity: T cells

9. Unique Characteristics of the Immune
Response
1. Specificity
 For example, immunization with poliovirus only protects against poliomyelitis, not
against the flu. The specificity of the immune response is due to the existence of
exquisitely discriminative antigen receptors on lymphocytes
2. Memory
 The ability to remember previous responses and to react more quickly and more
intensely.
 meaning that repeated exposures to a given antigen elicit progressively more
intense specific responses.

10. Stages of immune response
3 stages- induction, amplification and effector.
 Induction involves recognition of antigen by specific receptors on lymphocytes
.followed by activation of the cells.
 Amplification –cytokines mediate interaction between cells leading to proliferation
and differentiation of T and B lymphocytes.
 Effector- elimination of pathogens by antibodies, cytotoxic T cells or macrophages.

11. Innate immunity
 Exists prior to invasion (natural immunity).
 Non-specific,
 No memory
 Intact skin and mucous membranes acts as physical barrier to invasion by
microorganisms.
 Chemical properties such as gastric acid.
 Antibacterial substances found in secretions e.g lysozyme

12. Innate immunity
 Phagocytic cells Include neutrophils, macrophages, dendritic cells, natural killer
cells.
 They Ingest and neutralize microorganisms by exposing them to proteolytic
enzymes, lipases, hydrogen peroxide etc.
 They also act as antigen presenting cells to T lymphocytes bridging innate and
acquired immunity.

13. Acquired immunity
Involves 2 types ;
1. Humoral immunity:
 Involves the production of antibodies in circulation that eliminate infectious agent
 Mechanisms antibodies use include Neutralization/blocking, ADCC, Opsonization,
Complement fixation
2. Cell-mediated immunity:
 T cells activate macrophages to kill phagocytosed microbe or kill infected cells
 Cytolytic T cells kill infected cells with microbes (eg Viruses)

15. Comparison Between Innate and Acquired
Immunity
Innate Immunity: 1st and 2nd line of defense
 Immediate response with no improvement with repeated exposure
 React against microbes but not against noninfectious substances or host tissue
Adaptive or acquired immunity (3rd line of defense)
 Specificity: ability to recognize different microbes (self/non self recognition)
 Flexibility (adaptability): ability to recognize newly evolved microbes (diversity)
 Memory: ability to remember previous responses and to react more quickly and
more intensely

16. Development of cells of the immune system

17. Immune cells

18. Cells of the immune system
Lymphocytes
 B and T cells (Th/CD4 and Tc/CD8 cells)
 Natural killer cells (NK cells)
Antigen presenting cells
 B cells, monocytes/macrophages, dendritic cells
Cells that produce inflammatory mediators (granulocytes)
 Neutrophils, basophils, eosinophils, mast cells
 Important in helminth and protozoan infections
 Involved in allergy

19. Immune system
Antigen
 A toxin or other foreign substance which induces an immune response in the body, especially the
production of antibodies
 It can also be defined as non-self substances (cells, proteins) that are recognized by immune cells,
thereby eliciting an immune response.
Antibody
 Proteins found in blood and produced in response to a specific antigen
 They are released by B lymphocytes. A.k.a immunoglobulins.
Cytokines
 Substances / proteins made by certain immune and non-immune cells that have an effect on the
immune system
 important in cell to cell communication.
 Produced by a wide variety of cells including immune system cells.
 Classified according to action, eg chemokines- attract cells to areas of inflammation

20. Types of immunity
Active immunity
 Active Immunity results when exposure to a disease organism triggers the immune
system to produce antibodies to that disease.
 Active immunity can be acquired through natural immunity or vaccine-induced.
Passive immunity
 the short-term immunity which results from the introduction of antibodies from
another person or animal
 It is immediately available but does not last long.
***reading assignment, differences between active & passive immunity