The presentation delves into the intricate relationship between antigens and antibodies, unraveling the fundamental interactions within the immune system. Beginning with an introduction to the immune system's pivotal role in safeguarding the body from pathogens, it elaborates on the definition and types of antigens, elucidating their diverse forms and origins, spanning from bacteria and viruses to allergens. Insightful details elucidate the structural composition of antigens, highlighting their antigenic determinants or epitopes that provoke distinct immune responses. Shifting focus, the presentation explores the pivotal role of antibodies, delineating their functions and varied classes, from IgG to IgE. An emphasis is placed on the structural specificity of antibodies in recognizing antigens, using the lock-and-key model as an illustrative framework. It details the mechanisms underlying antibody-antigen interactions, elucidating neutralization, agglutination, and precipitation as pivotal immune responses.

1. Antigen-Antibody
Interaction
Let’s start Presentation

2. Table of contents
01 Introduction
How do antigens and antibodies interact?
Factors affecting antigen - antibody
interaction
Chemical bonds responsible for Antigen-
Antibody interaction
02
03
04
Types of antigen and antibody interaction
05
Application & Limitation
06

3. Introduction
01

4. Introduction to Antigen-Antibody
Interaction
 Antigen-antibody interaction is a specific
chemical interaction between antigens and
antibodies.
 It plays a crucial role in the immune response.
 Antibodies recognize and bind to antigens to
neutralize or destroy them.
 This interaction is fundamental in immunology
and forms the basis of various diagnostic tests.

5. How do antigens
and antibodies
interact?
02

6. Antigen: The Mysterious Invader
● Antigens are substances that can induce an
immune response in the body.
● They are usually foreign substances like
bacteria, viruses, or fungi.
● Antigens can also be toxins, chemicals,
drugs, or foreign particles like splinters.
● The body identifies antigens as foreign and
potentially harmful, triggering an immune
response.

7. Antibodies: Our Body’s Secret Weapons
● Antibodies are Y-shaped proteins produced by
B-cells, a type of white blood cell.
● They are part of the body's adaptive immune
response.
● Antibodies recognize and bind to specific
antigens.
● This binding helps neutralize the antigen,
marking it for destruction by other immune
cells.

8. How the lock and key concept relates
with antigen antibody interaction ?
● The interaction between antigens and antibodies can be related to a lock and key
mechanism.
● Each antibody has a unique design that fits into the shape of the antigen. When they
combine, a signal is delivered to the immune system, indicating that it is time to attack.
Antigen + Antibody ⇄ Ag-Ab complex → Immune Response

9. Factors affecting
antigen and antibody
interaction
03

10. Factors
1. Affinity and Specificity:
• Affinity: Strength of binding between antibody and antigen.
• Specificity: Antibody's preference for a particular antigen.
2. Epitope and Paratope:
• Epitope: Unique region on antigen interacting with antibody.
• Paratope: Corresponding region on the antibody.
3. Concentration:
• The concentration of antigen and antibodies affects interaction.
• Higher concentrations enhance binding chances.
4. Temperature:
• Temperature influences rate and strength of interaction.
• Higher temperatures lead to faster responses, but extremes can denature proteins.

11. Factors
1. pH:
• pH influences interaction by affecting charge and shape.
• Antibodies and antigens have ideal pH ranges for binding.
2. Ionic Strength:
• Solution's ionic strength impacts interaction.
• High salt concentrations disrupt electrostatic interactions.
3. Valence:
• Interaction strength affected by binding sites.
• Bivalent (IgG) antibodies have two sites; pentameric (IgM) have ten.

12. Factors
1. Size and Shape:
• Interaction influenced by size and shape of antigen and antibody.
• Strong interaction requires a good match between paratope and epitope.
2. Post-Translational Modifications:
• Glycosylation and phosphorylation alter shape and charge.
• Impact on interaction between antigens and antibodies.
3. Cross Reactivity:
• Antibody binds to antigens with structural similarities.
• Recognizes antigens other than the target.
4. Time:
• Antigen-antibody exposure time influences interaction.
• Longer incubation durations lead to more powerful binding.

13. Chemical bonds
responsible for Antigen-
Antibody interaction
04

14. Chemical Bonding
1. Hydrogen Bonding:
• Weak bonds form between amino acids in the antibody's variable region (CDRs) and
the epitope.
• Enhances the uniqueness and affinity of the interaction.
2. Electrostatic Interaction:
• Charged amino acid residues on the antibody and antigen interact.
• Positive and negative charges contribute to binding.
3. Van der Waals Forces:**
• Attractive forces caused by electron distribution changes.
• Form between nonpolar regions, contributing to complex stability.
4. Hydrophobic Interaction:
• Nonpolar portions of antibody and antigen avoid the aqueous environment.
• Facilitates stable binding.

15. Types of antigen
and antibody
interaction
05

16. Types of antigen and antibody interaction
In vivo In vitro
● Agglutination
● Opsonization
● Neutralization
● Complement activation
● Allergic reactions
● Immobilization
● Cross-linking
● Immune complex formation
● Immunoprecipitation
● ELISA (Enzyme-Linked
Immunosorbent Assay)
● Western blotting
● Immunofluorescence
● Immunohistochemistry
● Flow cytometry
● Radioimmunoassay
● Immunodiffusion

17. Invivo
1. Agglutination:
• Agglutination: Antibodies bind to multiple microorganism antigens, causing clumping.
Crucial in immune responses and lab tests.
• Antibodies bind to microorganism antigens, causing visible clumps. Vital in immunity
and lab diagnostics, occurring internally and in labs.
2. Opsonization:
• Antibody Binding: Opsonization begins with antibodies attaching to specific antigens
on pathogen surfaces through their Fab regions, ensuring precise recognition and
binding.
• Enhanced Phagocytosis: Antibodies act as "tags" for pathogens, facilitating
recognition by immune cells like macrophages and neutrophils, triggering
phagocytosis and subsequent destruction within phagolysosomes, eliminating the
pathogen.

18. Invivo
1. Neutralization
• Neutralization: Antibodies binding to antigens hinder their harmful effects, preventing
viruses or toxins from acting, aiding immune defense by neutralizing their impact.
• Harm Prevention: Antibodies binding to antigens stop pathogens or toxins from
causing harm, neutralizing their effects and supporting immune defenses.
2. Complement fixation:
• Antibodies activate the complement system when binding to antigens, leading to the
creation of a membrane attack complex that destroys pathogen cell membranes.
• Complement fixation enhances the immune response by increasing inflammation and
aiding in the clearance of antibody-bound pathogens.

19. Invitro
1. ELISA:
• ELISA: Detects specific antigens or antibodies in samples. Widely used in diagnostics
and research based on antibody-antigen interaction.
• Versatile Tool: Identifies targeted antibodies or antigens in samples. Essential in
clinical settings, research, and various industries.
2. Western blotting
• Protein Identification: Western blotting uses antibodies to detect specific proteins
transferred onto a membrane.
• Visualization: This technique employs primary and secondary antibodies to visualize
and quantify target proteins on the membrane.

20. Application
& Limitation
06

21. Application
● Blood Typing Applications:
○ Determines blood groups efficiently.
○ Supports rapid diagnostic tests (e.g., pregnancy testing, malaria, dengue)
completed within minutes.
● Serological Testing Functions:
○ Quantifies antigens.
○ Detects protein presence or absence in serum.
○ Investigates various immunodeficiency disorders' characteristics.
● Confirmatory Tests' Usage:
○ Techniques like Western Blotting confirm infections like HIV.
○ Ensures precise and accurate diagnosis.

22. Limitations
● Limited Access and Resources:
○ Advanced skills and equipment required for these procedures are often
unavailable in underprivileged or less developed regions, leading to infrequent
application.
● Limitation in Detecting Low Parasite Density:
○ Rapid Diagnostic Tests (RDTs) struggle to reliably detect low-density
parasitemia (e.g., 200 parasites/L).
● Challenges in Antibody Detection:
○ Difficulty distinguishing between early and late infections in antibody detection
due to antibodies persisting in the bloodstream long after the infection has
been cured.

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