module 12

What is the overall goal of the adaptive immune system?

responds to foreign microbes that have breached the external and internal innate defense mechanisms.

Name and explain the four principles of adaptive immunity.

Diversity: Able to respond to almost infinite number of antigens

Specificity: specific to a target antigen

Memory: recognizes antigens if they enter again

Differentiation: “self” from “non-self”

What are the cell types associated with humoral immunity?

B cells and Helper T cells (TH) cells

What are the goals of humoral immunity?

Works to eliminate extracellular antigens (bacteria, toxins, viruses in bloodstream or tissues)

Triggers production of proteins called antibodies that are specific for an antigen

Antibodies are only produced by activated B cells

Helper T cells are critical in activating B lymphocytes

Define the two types of MHC molecules, what type of antigens they present and what types of cells produce them.

MHC class I present endogenous antigens

Produced by all nucleated cells

MHC class II present exogenous antigens

Produced by antigen-presenting cells: dendritic cells, B cells, macrophages.

T cells able to recognize peptides being presented on MHC complexes

Summarize the steps of the humoral response. What is the outcome if a helper T cell recognizes the antigen presented on the B cell? What is the outcome if a helper T cell doesn’t recognize the antigen presented on the B cell?

Explain clonal selection theory and how it leads to selecting B cells for expansion.

We are born with a vast repertoire of B cells

Each displays many copies of Ig with the same antigen specificity

Binding to specific antigen “selects” a B cell for clonal expansion

What are the two main parts of an antibody? Which part is responsible for antigen binding?

the Fab fragment (fragment antigen binding) and the Fc fragment (fragment crystallizable)

Name the five types of IgG and their respective primary roles.

IgM

First class produced during primary response

Primary role in bloodstream infections

IgG

First and most abundant class produced during secondary response

Most abundant class in blood and tissue fluids

Provides longest-term protection

Can be transported across placenta to fetus

IgA

Most abundant class produced overall

Mucosal immunity: protects against toxins, viruses, and interferes with attachment of microbes to host cells

IgD

Development and maturation of antibody response

IgE

Responsible for allergic reactions

Summarize each of the following antigen-antibody outcomes:

Viral inhibition - antibodies attach to molecules on surface of viruses, preventing attachment to host cells

Agglutination - antibodies combine with antigens on the cell surface and bind the cells together, restricting movement

Precipitation - antibodies cause soluble antigens to precipitate

Neutralization - antibodies against toxins are called antitoxins; they bind to toxin molecules to neutralize them

Opsonization - enhance phagocytosis

Complement activation - antibodies bound to bacteria activate complement, resulting in bacterial lysis

Explain the difference between the primary and secondary immune response in terms of the number of IgG antibodies present, if the person actually becomes sick, and the response time.

PRIMARY

Immune response during first encounter with an antigen

Takes 10-14 days for substantial antibody accumulation

Person may be sick

Additional exposure to antigen yields much faster secondary response

SECONDARY

Significantly faster and more effective than primary

Memory B cells responsible for response

Greater numbers

Quickly become plasma cells that produce antibodies

Pathogen usually eliminated before causing harm

Vaccines exploits this natural phenomenon

Explain the cell types and goals associated with the cell-mediated immune response.

Cell types: T cells (cytotoxic and helper)

Goals: Deals with antigens residing with a host cell

Tumor cells, virally infected cells, bacteria that live within a host cell, protozoans

Production of T lymphocytes (T cells) directed against an antigen

Define the following for both cytotoxic and helper T cells:

Abbreviations - TH (T helper) TC or CTL (cytotoxic t cell)

Cluster of differentiation - CD4 (T helper) CD8 (cytotoxic t cell)

Functions T helper: activates b cells to produce antibodies; activates cytotoxic cells T cells; activates inflammatory cells. Cytotoxic T cells: killer cell that targets cells with foreign intracellular antigens, including viruses, bacteria and cancer cells

How and by what cells are T cells activated?

TC cells recognize antigens presented on MHC class I molecules

Cells present internal proteins on MHC class I molecule

Binding by TC cell indicates recognition of pathogen or cancer

TC induces apoptosis via release of proteases, cytotoxins (perforin)

Explain the process of immunization and what type of immune response it relies on.

Process of inducing immunity relies on production of memory B cells

Define and be able to recognize examples of the following types of immunity:

Natural active immunity - infection; contact with pathogen

Natural passive immunity - antibodies passed from mother to fetus via placenta; or infant to milk

Artificial active immunity - vaccine; or dead attenuated pathogens

Artificial passive immunity - infection of exogenous antibodies (gamma globulin)

What are the three goals of vaccination?

Production of memory B cells

Production of high antibody titers

Protection of individual AND population (Herd Immunity)

Explain how the concept of herd immunity relates to vaccination. What percentage of a population typically has to be vaccinated in order to achieve herd immunity?

Critical portion of population is immune to disease due to vaccination efforts

Infectious agent unable to spread due to insufficient susceptible hosts

What are the three general requirements associated with an ideal vaccine? What are some of the factors that affect “stability”?

Safety, effectiveness, stability

Affordability, administration as nasal spray or edible vaccine, no need for refrigeration, one dose or one shot, long shelf life

Why is childhood vaccination so important? Summarize how the Disneyland measles outbreak is an example of how the anti-vaccination movement is leading the re-emergence of vaccine preventable diseases.

Many still become ill or die from preventable diseases

Rise in vaccine hesitancy has lead to re-emergence of many vaccine-preventable childhood illnesses and related deaths

Started with an unvaccinated 11 year old with onset of symptoms in December who visited Disneyland

May 1, 2025, 935 confirmed measles cases. 3 deaths.

Fill in the following table for attenuated and inactivated vaccines:

Composition

Principle

Advantages

Disadvantages

Examples

Attenuated

“Live”, weakened version of organism/virus you are trying to vaccinate against

Replicates in recipient eliciting an immune response

Disease undetectable or mild

Single dose usually induces long-lasting immunity due to microbe multiplying in body

Can sometimes cause disease in immunosuppressed individuals

Not recommended for pregnant women

Usually require refrigeration to keep active

Measles, mumps, rubella, chickenpox, yellow fever

Inactivated

Whole organism/virus (dead)

Presence of organism/virus will still elicit immune response due to presence of associated antigens, but will not actively multiply in the body

Viral versions will only produce humoral response because dead virus can’t infect cells

Cannot revert to pathogenic form and cause disease

No replication → no amplification in vivo → immune response is limited

Booster doses usually required

Rabies, cholera, pertussis, influenza

Explain the composition and list examples of the following vaccine types:

Toxoids - Composition: toxins treated to destroy toxic part but retain antigen

Examples: diphtheria, tetanus

Subunit - Composition: consist of key protein antigens or antigenic fragments from pathogen

Examples: bacterial meningitis, acellular pertussis

Virus-like Particle - Composition: empty capsids produced by genetically engineered organisms

Example: HPV

Polysaccharide - Composition: made from capsules

Examples: pneumococcal vaccine for adults

What type of vaccine are the two promising COVID-19 vaccines currently in trial by Moderna and Pfizer? How does this type of vaccine work? What is the main disadvantage?

mRNA vaccine

Principal: mRNA able to enter and be translated by our cells

Programs our cells to create viral spike proteins that the immune system can recognize and mount a response against

COmposition: Manufactured piece of mRNA that codes for antigen of pathogen

In case of COVID-19 → coding for spike protein