PMI 128: Lecture 12-13

What are APCs

Antigen presenting cells

What are the APCs we have gone through in lecure?

macrophages and dendritic cells

What are the T cells we have gone over in class?

CD4+ T helper cells and CD8+ T cells

What are the B cells we have gone over in lecture?

Antibody secreting cells

What are the stages of virus dissemination and immune response?

Virus binds to epithelial cells

Replication and local spread of infection

Spread to lymphatics

Adaptive immunity takes over

What is the role of antigen-presenting cells (APCs) in the immune response to viral infections?

Pick up antigens, process them, and present them to T cells, initiating an adaptive immune response

e.g. macrophages and dendritic cells

What is the primary function of CD4+ T helper cells in the

Activate other immune cells (such as B cells and CD8+ T cells) by releasing cytokines, which help direct the immune response.

What do CD8+ cytotoxic T cells do during an immune response?

Recognize and kill virus-infected cells by releasing perforins and granzymes that induce apoptosis in infected cells.

What is the main function of B cells in the immune system?

Secrete antibodies (IgA, IgG, IgM), neutralize pathogens, and activate the complement system. They also present antigens to T cells.

How does adaptive immunity differ from innate immunity?

Specific to particular pathogens, develops memory, and involves T and B cells.

Innate immunity is a general, immediate response to pathogens

What is the process of exogenous antigen processing?

(from outside the cell)

Internalized, processed in phagolysosomes, and presented on MHC class II molecules to CD4+ T cells.

What is the process of endogenous antigen processing?

(from inside infected cells)

In the ER, presented on MHC class I molecules to CD8+ T cells.

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

H- involves antibodies produced by B cells to neutralize pathogens.

CM- involves T cells (CD4+ and CD8+) that kill infected cells or help activate other immune cells

What is the primary function of secretory IgA?

Crucial for immune defense at mucosal surfaces, such as the GI tract and respiratory tract, where it neutralizes viruses and prevents them from entering cells.

What are the key roles of cytotoxic T lymphocytes (CTLs) during a viral infection?

Recognize infected cells presenting viral peptides on MHC class I

Kill infected cells via apoptosis

Release antiviral cytokines like IFN-γ.

How do memory T cells contribute to long-term immunity?

They remain after an infection, enabling a faster and more robust immune response upon re-exposure to the same pathogen.

What is antibody-dependent enhancement (ADE), and how does it affect dengue virus infection?

Occurs when antibodies from a previous infection bind to a different serotype of the virus, facilitating viral entry into cells, worsening the infection (seen in dengue virus).

What is the difference between cytopathic and non-cytopathic viruses in terms of immune response?

C-cause direct cell damage

N.C- do not kill cells but may induce an immune response that causes tissue damage.

How do regulatory T cells (Tregs) suppress immune responses during viral infections?

They release IL-10 and TGF-β to suppress immune activation, helping to prevent excessive inflammation and tissue damage.

What is immunopathology in viral infections?

Refers to tissue damage caused by the immune response itself, such as cytotoxic T cell-mediated tissue destruction during viral infections.

What is immune memory, and how does it contribute to protection from reinfection?

Allows the immune system to quickly recognize and respond to a previously encountered pathogen. Memory cells (T and B cells) facilitate faster and stronger immune responses to reinfection.

How does the immune response to measles unfold over time?

Peaks around day 8 for CD4+ helper cells and day 12 for CD8+ cytotoxic T cells. IgM appears around day 14, and IgG peaks three weeks after infection.

Why is CD8+ T cell activation essential for controlling influenza?

Crucial for killing influenza-infected cells. They can quickly eliminate the virus, limiting its replication and spread.

What is original antigenic sin in the context of influenza infections?

Refers to the phenomenon where the immune system responds to new strains of influenza based on previous strains it encountered, potentially reducing the effectiveness of the immune response.

How do NK cells contribute to viral immunity?

Recognize virus-infected cells that have downregulated MHC class I expression and kill them through antibody-dependent cellular cytotoxicity (ADCC) and direct cytotoxic activity

What is the function of T helper 1 (Th1) cells in immune responses?

Promote cell-mediated immunity, releasing cytokines like IFN-γ that activate cytotoxic T cells, macrophages, and promote inflammation.

What role does T helper 2 (Th2) play in the immune system?

Support humoral immunity by stimulating B cells to produce antibodies, particularly in response to extracellular pathogens like viruses.

How does MHC class I restriction affect immune responses to viral infections?

Present viral peptides to CD8+ T cells. The immune system recognizes and targets infected cells for destruction, a key mechanism in controlling viral infections.

What are the consequences of immunodeficiencies like DiGeorge syndrome?

Results in a lack of functional T cells, making individuals highly susceptible to viral infections like measles, which can be fatal without T cell immunity.

What are macrophages and dendritic cells categorized as in the immune response?

Are antigen-presenting cells (APCs).

They process antigens and present them to T cells, initiating the adaptive immune response.

How does antibody-dependent cellular cytotoxicity (ADCC) work?

NK cells recognize and kill virus-infected cells that have antibodies bound to their surface, enhancing immune surveillance and killing of infected cells.

What are the primary lymphoid organs, and what is their role in immune cell development?

Are the thymus (where T cells mature) and bone marrow (where B cells are produced).

They are essential for the development and differentiation of immune cells.

What does the MHC class II molecule present, and which cells recognize it?

Present exogenous antigens to CD4+ T cells, activating helper T cells and initiating the adaptive immune response.

What is the main difference between MHC class I and MHC class II in antigen presentation?

MHC class I presents endogenous antigens (from within the cell, like viral proteins) to CD8+ cytotoxic T cells

MHC class II presents exogenous antigens to CD4+ helper T cells

How does the immune system differentiate between self and non-self during viral infections?

The immune system uses MHC molecules (I and II) to display self and non-self antigens. Self peptides are recognized as normal, while non-self viral peptides are targeted for immune destruction.

What is the difference between primary and secondary antibody responses?

The primary antibody response is slower and involves the production of IgM first, while the secondary antibody response is faster, involves higher levels of IgG, and provides longer-lasting immunity.

What is the significance of Treg cells in controlling immune responses?

Help suppress excessive immune responses and prevent autoimmune diseases by producing anti-inflammatory cytokines like IL-10 and TGF-β.

What is immunopathology, and how does it relate to viral diseases?

Refers to tissue damage caused by the immune system's response to a viral infection, such as the damage caused by cytotoxic T cells or excessive inflammation.

What is the importance of memory B cells in viral immunity?

They remember previous infections and can rapidly differentiate into plasma cells that produce antibodies if the virus is encountered again, leading to a quicker immune response.

What is the function of complement in viral immunity?

Helps to tag viruses for destruction, lyse infected cells, and enhance phagocytosis of pathogens through opsonization.

What is antibody neutralization, and why is it important in viral infections?

Occurs when antibodies bind to viral particles, preventing them from entering host cells and thus blocking infection.

What is the role of NK cells in defending against viral infections?

Recognize and kill virus-infected cells, especially those with low MHC class I expression, and contribute to immune surveillance and antibody-dependent cellular cytotoxicity (ADCC).

What happens during the acute phase of a viral infection in terms of immune response?

Innate immunity is critical for initial viral clearance. Adaptive immunity (T and B cells) develops later, leading to viral neutralization and destruction.

Adaptive immunity

Specific to particular pathogens, develops memory, and involves T and B cells

Innate immunity

General, immediate response to pathogens