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Diseases and Immunity - Antibodies and vaccination

Grade 12IGCSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Antigens are molecules, typically proteins or glycoproteins, located on the surface of pathogens that are recognized as 'non-self' by the immune system, triggering an immune response.

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Antibodies, also known as immunoglobulins (IgIg), are YY-shaped globular proteins produced by plasma cells (derived from BB-lymphocytes).

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The basic structure of an antibody consists of four polypeptide chains: two identical heavy (HH) chains and two identical light (LL) chains, represented by the formula H2L2H_2L_2.

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Antibodies possess a 'variable region' with a specific 3D3D tertiary structure complementary to a specific antigen, forming an antigen-antibody complex.

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Active Immunity is acquired when the body produces its own antibodies and memory cells (BmemoryB_{memory} and TmemoryT_{memory}) following exposure to a pathogen or a vaccine.

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Passive Immunity is the short-term immunity resulting from the introduction of antibodies from another source, such as IgGIgG passing through the placenta or IgAIgA in breast milk.

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The Secondary Immune Response is characterized by a shorter lag phase, a faster rate of antibody production, and a significantly higher peak concentration ([Ab][Ab]) compared to the primary response.

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Vaccination involves the deliberate exposure to harmless antigenic material (e.g., attenuated pathogens or mRNAmRNA sequences) to stimulate the production of memory cells without causing disease.

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Herd Immunity occurs when a large enough proportion of the population (PcP_c) is immune, reducing the probability of transmission to non-immune individuals.

📐Formulae

H2L2H_2L_2

[Ab]secondary>[Ab]primary[Ab]_{secondary} > [Ab]_{primary}

Pc=1−1R0P_c = 1 - \frac{1}{R_0}

V=INV = \frac{I}{N}

💡Examples

Problem 1:

During a secondary immune response, the concentration of antibodies [Ab][Ab] in the blood increases much more rapidly than in the primary response. If the primary response reaches a peak concentration of 10110^1 units/mL in 1414 days, and the secondary response reaches 10410^4 units/mL in 33 days, calculate the factor of increase in peak antibody concentration.

Solution:

The factor of increase is calculated by dividing the secondary peak by the primary peak: 104101=103=1000\frac{10^4}{10^1} = 10^3 = 1000.

Explanation:

The presence of BmemoryB_{memory} cells allows the body to bypass the initial clonal selection phase, leading to immediate clonal expansion into plasma cells, resulting in a 10001000-fold increase in antibody production.

Problem 2:

A specific pathogen has a basic reproduction number R0=5R_0 = 5. Calculate the critical vaccination threshold (PcP_c) required to achieve herd immunity within the population.

Solution:

Using the formula Pc=1−1R0P_c = 1 - \frac{1}{R_0}: Pc=1−15P_c = 1 - \frac{1}{5} Pc=1−0.2=0.8P_c = 1 - 0.2 = 0.8

Explanation:

To stop the spread of the disease, at least 80%80\% (or 0.80.8) of the population must be immune through vaccination or prior infection.

Problem 3:

Describe the chemical interactions that allow an antibody to bind to an antigen.

Solution:

The binding occurs at the variable region via non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions.

Explanation:

Because the variable region is specific to the 3D3D shape of the antigen, the sum of these weak forces allows for a high-affinity H2L2H_2L_2-antigen complex.

Antibodies and vaccination - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology