Adaptive Immunity and Vaccines

These flashcards summarize key concepts related to adaptive immunity, the role of various immune cells, and mechanisms of vaccination.

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

Humoral immunity involves B cells and antibodies, while cell-mediated immunity involves T cells.

What are the roles of B cells in humoral immunity?

Upon activation, B cells differentiate into plasma cells, which are antibody-secreting factories, and memory B cells. Antibodies then neutralize extracellular pathogens and toxins, facilitate opsonization, and activate the complement system.

What is the role of T helper cells in humoral immunity?

T helper cells assist in activating B cells and stimulating antibody production.

What is the function of Major Histocompatibility Complexes (MHC) in cell-mediated immunity?

MHC molecules present antigens to T cells to activate the immune response.

What are antigens?

Antigens are molecules, typically proteins or polysaccharides found on pathogens or toxins, that can bind specifically to B-cell receptors (BCRs) or T-cell receptors (TCRs) and elicit an adaptive immune response.

What is the definition of vaccines?

Biological preparations that provide acquired immunity to a particular disease.

How do vaccines work?

Vaccines introduce specific antigens, derived from inactive, attenuated pathogens or their components, to stimulate the adaptive immune system to develop immunological memory and long-term protection without causing disease.

What are the key features of adaptive immunity?

Specificity and memory for previously encountered pathogens.

What is the primary response to an antigen?

The immune response that occurs upon first exposure to a pathogen or vaccine.

What is the role of memory in adaptive immunity?

Memory allows for a quicker and stronger response upon re-exposure to the same pathogen.

What types of cells are involved in adaptive immunity?

The primary cells involved in adaptive immunity are B lymphocytes (B cells), which are responsible for humoral immunity, and T lymphocytes (T cells), which mediate cell-mediated immunity. Within T cells, there are helper T cells (CD4+) and cytotoxic T cells (CD8+).

What is the difference between active and passive immunization?

Active immunization involves stimulation of the immune system, while passive immunization involves direct transfer of antibodies.

What are the five main classes of antibodies?

IgG, IgM, IgA, IgD, and IgE.

What is the main function of IgG antibodies?

IgG antibodies neutralize pathogens and toxins, and provide passive immunity to the fetus.

What is the structure of an antibody?

An antibody (immunoglobulin) is a Y-shaped glycoprotein composed of two identical heavy chains and two identical light chains, linked by disulfide bonds. It features antigen-binding sites at the tips of the 'Y' and a constant region that interacts with immune cells.

What are epitopes?

Small, exposed regions on an antigen recognized by antibodies and T cells.

What is the function of haptens?

Haptens are small molecules that become antigenic when attached to a larger carrier molecule.

How do antibodies neutralize pathogens?

Antibodies bind to epitopes on pathogens or toxins, preventing them from attaching to host cells.

What is agglutination in the immune response?

Agglutination is the process where multivalent antibodies bind to and cross-link multiple antigens on the surface of pathogens (like bacteria or viruses), causing them to clump together. This clumping enhances their clearance by phagocytes.

What is the classical complement pathway?

A mechanism triggered by antibodies binding to pathogen surfaces that promotes inflammation and phagocytosis.

What is antibody-dependent cell-mediated cytotoxicity (ADCC)?

A process where antibodies bind to large pathogens, facilitating their destruction by immune effector cells.

What is the difference between MHC class I and MHC class II?

MHC class I is found on all nucleated cells and presents antigens to CD8 T cells, while MHC class II is found on APCs and presents antigens to CD4 T cells.

What are antigen-presenting cells (APCs)?

Cells that present antigens on MHC II to activate helper T cells.

What is the process of thymic selection?

A process that selects functional T cells and removes those that are self-reactive.

What are the three main outcomes of thymic selection?

Selection for functional TCRs, appropriate MHC interactions, and removal of self-reacting cells.

What is peripheral tolerance?

A mechanism that prevents self-reactive T cells from causing autoimmune disease after they exit the thymus.

What are mature naïve T cells?

T cells that have exited the thymus and are capable of activation, but have not yet encountered their specific antigen.

What surface molecules are used to identify helper T cells?

Helper T cells express CD4 surface molecules.

How do B cells recognize antigens?

B cells recognize free antigens using B cell receptors (BCRs).

What are the roles of memory B cells?

Memory B cells ensure a rapid and strong secondary response upon subsequent exposures to an antigen.

What is T-dependent activation of B cells?

A process requiring help from helper T cells to fully activate B cells.

What is the purpose of class switching in B cells?

Class switching allows B cells to produce different antibody classes while retaining the same epitope specificity.

What occurs during the primary response to an antigen?

There is a lag period before antibody levels rise, generally taking 10 days, with IgM produced first, followed by IgG.

How does the secondary response differ from the primary response?

The secondary response is faster, more robust, and produces higher levels of IgG antibodies with greater affinity.

What is apoptosis in the context of T cell activation?

A programmed cell death mechanism that eliminates self-reactive thymocytes during thymic selection.

What triggers superantigen activity?

Superantigens activate T cells non-specifically, leading to a massive cytokine storm.

How do T cells kill infected cells?

T cells recognize infected cells through their TCR and release cytotoxic proteins such as perforin and granzymes.

What is the significance of memory T cells?

Memory T cells provide quick responses to re-infection by the same pathogen.

How are T-independent B-cell responses characterized?

Responses to T-independent antigens do not require T-cell help and are short-lived.

What happens during B-cell clonal expansion?

Activated B cells proliferate and differentiate into plasma cells that secrete antibodies.

What structure do B-cell receptors (BCRs) have?

BCRs are Y-shaped molecules composed of heavy and light chains, with antigen-binding sites.

What are the components of the immune system involved in T-cell activation?

T-cell activation involves recognition of antigen-MHC complexes and co-stimulatory signals from APCs.

What is the role of cytokines in T cell activation?

Cytokines released from APCs and T cells stimulate T cell activation and differentiation.

What are the primary targets of humoral immunity?

Extracellular pathogens and their toxins.

How does genetic rearrangement contribute to TCR diversity?

Genetic rearrangement (V(D)J recombination) generates diverse TCRs by combining different gene segments.

What is the role of dendritic cells in antigen presentation?

Dendritic cells phagocytose pathogens and present antigens on MHC II to activate helper T cells.

What distinguishes innate immunity from adaptive immunity?

Innate immunity is non-specific and immediate, while adaptive immunity is highly specific and has memory.

What is the function of IgE antibodies?

IgE plays a critical role in anti-parasitic defense and allergic reactions.

What is the significance of the heavy chain isotype in antibody classes?

It determines the function, location, and properties of the antibody.

What are some examples of PAMPs recognized by the innate immune system?

Lipopolysaccharides (LPS) and peptidoglycan.

How do antibodies facilitate opsonization?

Antibodies coat pathogens, enhancing their recognition by phagocytes and promoting engulfment.

What is the role of regulatory T cells (Tregs)?

Tregs help maintain peripheral tolerance and prevent autoimmunity by inhibiting other T cells.