HI06 - Introduction to Adaptive Immunity

What are the two main branches of the immune system?

The innate and adaptive immune systems.

How does innate immunity recognize pathogens?

It recognizes general molecular patterns called MAMPs using pattern recognition receptors (PRRs).

How does adaptive immunity recognize pathogens?

It recognizes unique antigenic epitopes specific to individual pathogens using B and T cell receptors.

What are the six major differences between innate and adaptive immunity?

Specificity, speed, receptor origin, target recognition, response memory, and response consistency.

What is an antigen?

Any molecule recognized and bound by an antibody, B cell receptor, or T cell receptor.

What is an immunogen?

A molecule capable of activating B or T cells to produce an immune response.

What is immunogenicity?

The ability of a substance to elicit an immune response.

What is an epitope?

The specific portion of an antigen that binds to an antibody or antigen receptor.

What is a hapten?

A small molecule that becomes immunogenic only when attached to a larger carrier molecule.

What is clonal expansion?

The process where activated B or T cells divide to produce many identical copies with the same receptor specificity.

What is anergy?

A state in which a B or T cell becomes unresponsive after recognizing an antigen without receiving a second activation signal.

How do innate immune cells recognize pathogens?

Through pattern recognition receptors (PRRs) that detect MAMPs or DAMPs

How do adaptive immune cells recognize pathogens?

Through unique antigen receptors specific to individual epitopes.

What genetic process creates receptor diversity in B and T cells?

Somatic recombination (VDJ recombination).

What is somatic recombination?

Process in which Variable, Diversity, and Joining gene segments are rearranged in developing lymphocytes to generate diverse receptors.

What determines a lymphocyte’s receptor repertoire?

The specific VDJ gene rearrangements formed before antigen exposure.

What are the three structural regions of B and T cell receptors?

Transmembrane (anchoring and signaling), constant (function), and variable (antigen binding) regions.

What is the main structural difference between B and T cell receptors?

B cell receptors have heavy and light chains; T cell receptors have alpha and beta (or gamma and delta) chains.

What is unique about B cell receptor function?

They can bind directly to native 3D antigens and exist as membrane-bound or secreted antibodies.

What is unique about T cell receptor function?

They recognize short, linear peptides presented by MHC molecules and are only membrane-bound.

Do T cell receptors undergo somatic hypermutation or affinity maturation?

No, T cell receptors do not change after formation.

What are immature B and T cells?

Cells still developing their receptors in the bone marrow (B) or thymus (T).

What are naïve B and T cells?

Cells with functional receptors that have not yet encountered their specific antigen.

What are activated B and T cells?

Cells that have recognized their antigen and received a secondary activation signal.

What are effector B and T cells?

Differentiated cells that carry out immune functions, such as plasma cells (B) or cytotoxic/helper T cells.

What are the two classes of MHC molecules?

MHC Class I and MHC Class II.

Which cells express MHC Class I?

All nucleated cells (except red blood cells).

Which cells express MHC Class II?

Only professional antigen-presenting cells (APC): dendritic cells, macrophages, and B cells.

What type of peptides do MHC Class I molecules present?

Endogenous peptides produced inside the cell.

What type of peptides do MHC Class II molecules present?

Exogenous peptides taken up from outside the cell.

Which T cells recognize MHC Class I molecules?

CD8+ cytotoxic T cells.

Which T cells recognize MHC Class II molecules?

CD4+ helper T cells.

What two signals are required for T cell activation?

1) Antigen recognition via MHC binding, and 2) a co-stimulatory signal from an antigen-presenting cell.

What happens if a T cell recognizes an antigen without co-stimulation?

It becomes anergic or differentiates into a regulatory T cell.

What is the effector function of CD8+ T cells?

They kill infected cells by inducing apoptosis and secrete cytokines to enhance immune responses.

What are the main effector functions of CD4+ T helper cells?

They activate B cells and macrophages and coordinate immune responses via cytokine secretion.

What two signals are required for B cell activation?

1) Binding antigen via its B cell receptor, and 2) activation signal from a CD4+ T helper cell.

What happens if a B cell does not receive help from a T helper cell?

It becomes anergic and unresponsive.

What is the main effector cell derived from activated B cells?

Plasma cells, which secrete large amounts of antibodies.

What type of adaptive immunity do antibodies mediate?

Humoral immunity.

What is the main difference between humoral and cell-mediated immunity?

Humoral immunity targets extracellular pathogens; cell-mediated immunity targets intracellular pathogens.