🎓 M.Sc. Microbiology • Semester 1

MB 502 Immunology

Complete syllabus-based study notes covering fundamental immunology, immune responses, immunological techniques, immunopathology and vaccinology.

About MB 502

Immunology is the study of the immune system, its cells, tissues, molecules and mechanisms involved in protection against infectious agents and other foreign substances.

This course covers innate and adaptive immunity, complement, antigens, antibodies, antigen-antibody reactions, cell-mediated immunity, cytokines, immune disorders, immunopathology and vaccines.

Course: MB 502 Immunology | 3 Credits | Full Marks: 75
TOPIC 01

Basic Concepts of Immunology

1.1 Immunology

Immunology is the branch of biological science concerned with the study of the immune system, including immune cells, tissues, organs, molecules and immune responses.

1.2 Immunity

Immunity is the ability of an organism to recognize and defend itself against foreign substances, particularly infectious microorganisms.

Type Main Feature
Innate immunity Present from birth; rapid and largely non-specific.
Adaptive immunity Antigen-specific response with immunological memory.

1.3 Human Lymphatic System

The lymphatic system consists of lymph, lymphatic vessels, lymph nodes and lymphoid organs. It contributes to immune surveillance, transport of lymphocytes and maintenance of tissue fluid balance.

1.4 Primary Lymphoid Organs

Lymphocytes develop and mature in primary lymphoid organs. B cells mature mainly in bone marrow, whereas T-cell maturation occurs in the thymus.

1.5 Secondary Lymphoid Organs

1.6 Major Components of the Immune System

Exam focus: Compare innate and adaptive immunity and explain primary and secondary lymphoid organs.
TOPIC 02

Innate Immunity

2.1 Host–Pathogen Interaction

Host–pathogen interaction describes the dynamic relationship between an invading microorganism and the host. The outcome depends on microbial virulence factors and host defense mechanisms.

2.2 Non-specific Defense

Innate defense mechanisms act rapidly and do not require previous exposure to a particular pathogen.

2.3 Physical and Anatomical Barriers

2.4 Chemical Barriers

2.5 Cellular Components

2.6 Phagocytosis

Phagocytosis is the process by which specialized cells engulf and destroy microorganisms and cellular debris.

  1. Chemotaxis
  2. Attachment and recognition
  3. Engulfment
  4. Formation of phagosome
  5. Fusion with lysosome
  6. Microbial killing and digestion
  7. Removal of residual material
Important: Opsonization enhances phagocytosis. Major opsonins include IgG and complement component C3b.
TOPIC 03

Complement System

Complement is a group of plasma and membrane-associated proteins that participate in innate and adaptive immune defense.

3.1 Classical Pathway

The classical pathway is usually initiated when antibodies, particularly IgM or IgG, bind antigen. This leads to activation of C1 and subsequent complement reactions.

Antigen–Antibody Complex → C1 Activation → C4/C2 → C3 Convertase → C3 Activation → C5–C9 → Membrane Attack Complex

3.2 Alternative Pathway

The alternative pathway can be activated directly on microbial surfaces and does not require antibody.

Microbial Surface → C3 Activation → C3 Convertase → C5 Convertase → Membrane Attack Complex

3.3 Major Functions of Complement

Remember: C3 is a central component of complement activation. C3b is important in opsonization, while C5a is a powerful inflammatory mediator and chemotactic factor.
TOPIC 04

Cells and Tissues of Adaptive Immunity

4.1 T Lymphocytes

T lymphocytes mature in the thymus and are mainly involved in cell-mediated immune responses.

Cell Major Function
Helper T cell (CD4+) Coordinates immune responses through cytokine secretion.
Cytotoxic T cell (CD8+) Kills infected and abnormal cells.
Regulatory T cell Suppresses excessive immune responses and contributes to tolerance.

4.2 B Lymphocytes

B lymphocytes are responsible mainly for humoral immunity. Following activation, B cells can differentiate into antibody-secreting plasma cells and memory B cells.

4.3 Lymphocyte Development

Development involves maturation, antigen recognition, activation, clonal expansion and differentiation.

Clonal selection: An antigen selectively activates lymphocytes bearing receptors capable of recognizing that antigen. Activated cells proliferate and differentiate into effector and memory populations.
TOPIC 05

Antigens

5.1 Definition

An antigen is a substance that can be specifically recognized by components of the adaptive immune system, such as antibodies or antigen receptors of lymphocytes.

5.2 Immunogen and Antigen

An immunogen is an antigen capable of inducing an immune response. Thus, antigenicity and immunogenicity are related but distinct concepts.

5.3 Types of Antigens

5.4 Properties Affecting Antigenicity

Exam focus: Define antigen and immunogen and explain the conditions required for immunogenicity.
TOPIC 06

Antibodies and Immunoglobulins

6.1 Basic Structure

Immunoglobulins are glycoproteins produced by plasma cells in response to antigenic stimulation. A typical antibody contains two heavy chains and two light chains connected by disulfide bonds.

6.2 Antibody Regions

6.3 Immunoglobulin Classes

Class Main Features
IgG Major serum immunoglobulin; important in secondary immune responses and opsonization.
IgM First major antibody produced during a primary response; efficient complement activator.
IgA Important in mucosal secretions and mucosal immunity.
IgE Associated with allergy and defense against helminths.
IgD Mainly associated with B-cell surfaces and B-cell activation.

6.4 Genetic Basis of Antibody Diversity

Antibody diversity arises through mechanisms including V(D)J gene rearrangement, junctional diversity, combinatorial diversity and somatic hypermutation.

6.5 Class Switching

During an immune response, activated B cells can change the antibody class they produce without changing antigen specificity. This is called class-switch recombination.

Remember: Class switching changes the antibody effector function, whereas the antigen-binding specificity is retained.
TOPIC 07

In Vitro Antigen–Antibody Reactions

7.1 Precipitation

Precipitation occurs when soluble antigen reacts with its specific antibody to form an insoluble lattice under appropriate conditions.

Examples

7.2 Agglutination

Agglutination is the visible clumping of particulate antigens due to specific antibody-mediated cross-linking.

Types

7.3 Antibody Labelling

Antibodies can be labelled with fluorescent dyes, enzymes, radioisotopes or other detectable markers to identify specific antigens.

7.4 Immunofluorescence

Immunofluorescence uses fluorescently labelled antibodies for detection of specific antigens or antibodies.

7.5 ELISA

Enzyme-linked immunosorbent assay uses an enzyme-labelled antibody or antigen and an enzyme substrate to generate a measurable signal.

Antigen/Antibody → Enzyme-labelled reagent → Substrate → Colour development → Measurement

7.6 Radioimmunoassay

Radioimmunoassay uses a radioactive label to detect or quantify antigen or antibody with high sensitivity.

7.7 Immunoelectrophoresis

Immunoelectrophoresis combines electrophoretic separation of proteins with antigen-antibody precipitation.

7.8 Immunoblotting

Immunoblotting, commonly called Western blotting when applied to proteins, involves electrophoretic separation, transfer to a membrane and detection using specific antibodies.

Very important for exams: ELISA, immunofluorescence, agglutination, precipitation and immunoblotting can be prepared separately with principle, procedure, interpretation and applications.
TOPIC 08

Cell-Mediated Immune Response

8.1 Cells Involved

8.2 Major Histocompatibility Complex

Major histocompatibility complex (MHC) molecules present peptide antigens to T lymphocytes.

MHC Main Association
MHC Class I Present on most nucleated cells; presents endogenous peptides mainly to CD8+ T cells.
MHC Class II Mainly on professional antigen-presenting cells; presents exogenous peptides to CD4+ T cells.

8.3 Antigen Processing and Presentation

Antigen processing converts proteins into peptide fragments that can associate with MHC molecules and be recognized by T-cell receptors.

8.4 Effector Mechanisms

TOPIC 09

Cytokines and Toll-Like Receptors

9.1 Cytokines

Cytokines are small signalling proteins that regulate immune responses, inflammation, hematopoiesis and communication between immune and non-immune cells.

9.2 Important Cytokine Groups

9.3 Functions

9.4 Toll-Like Receptors

Toll-like receptors (TLRs) are pattern-recognition receptors that recognize conserved microbial structures known as pathogen-associated molecular patterns.

TLR Example Representative Ligand
TLR2 Components of Gram-positive bacteria and other microbial structures
TLR4 Lipopolysaccharide of Gram-negative bacteria
TLR5 Bacterial flagellin
TLR3 Double-stranded viral RNA
TOPIC 10

Immune Disorders

10.1 Immunological Tolerance

Immunological tolerance is a state in which the immune system does not mount an inappropriate response against a particular antigen, especially self-antigens.

10.2 Hypersensitivity

Hypersensitivity refers to excessive or inappropriate immune responses that cause tissue injury.

Type General Mechanism
Type I IgE-mediated immediate hypersensitivity
Type II Antibody-mediated cell or tissue injury
Type III Immune-complex mediated injury
Type IV T-cell mediated delayed hypersensitivity

10.3 Autoimmunity

Autoimmunity occurs when immune responses are directed against self-antigens.

10.4 Allergy

Allergy is an exaggerated immune response to ordinarily harmless environmental substances known as allergens.

10.5 Immunodeficiency

Immunodeficiency results from inadequate or defective immune function.

Exam focus: Prepare the four types of hypersensitivity with mechanism and examples as a separate long-answer topic.
TOPIC 11

Immunopathology of Bacterial, Viral and Parasitic Infections

Immunopathology refers to tissue or organ damage resulting from an immune response during infection. The immune response may protect the host but can also contribute to disease.

11.1 Bacterial Infections

Bacterial disease may involve inflammation, toxin-mediated damage, immune-complex formation, excessive cytokine responses or tissue destruction caused by immune cells.

11.2 Viral Infections

Viral infections may cause tissue damage directly through viral replication or indirectly through cytotoxic T-cell responses, inflammatory mediators and other immune mechanisms.

11.3 Parasitic Infections

Parasites can induce strong immune responses involving antibodies, eosinophils, macrophages and T-helper responses. Persistent infection may lead to chronic inflammation and tissue pathology.

Key concept: In infectious disease, pathology may result from the microorganism itself, the host immune response, or a combination of both.
TOPIC 12

Vaccinology

12.1 Vaccine and Vaccination

A vaccine is a biological preparation designed to induce protective immune responses against a specific pathogen or antigen. Vaccination is the administration of a vaccine to induce such protection.

12.2 Major Types of Vaccines

12.3 Attenuation

Attenuation is the reduction of the pathogenicity of a microorganism while retaining sufficient immunogenic properties for vaccine development.

12.4 Vaccine Production

Vaccine development and production involve antigen selection, production or propagation, purification, formulation, quality control, safety testing and evaluation of immune response.

12.5 Quality and Efficacy

Vaccines must undergo quality and safety evaluation. Vaccine efficacy describes protection under controlled study conditions, whereas effectiveness refers to performance under real-world conditions.

12.6 Adverse Events Following Immunization

An adverse event following immunization (AEFI) is any untoward medical occurrence following immunization. An AEFI does not necessarily imply that the vaccine caused the event.

12.7 Recent Developments

Modern vaccinology includes recombinant antigen production, viral-vector platforms, nucleic-acid vaccines, novel adjuvants and improved vaccine delivery systems.

Exam focus: Prepare vaccine types, attenuation methods, vaccine production, quality control, efficacy, adverse events and recent developments.

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