Immunology Overview Quiz

Learning Objectives

• Compare and contrast innate and adaptive immunity
• Describe the role of T cells and B cells in immunity
• Describe local inflammation

Innate Immunity (Nonspecific)

• Local response to protect against pathogens and toxins
• Born with these defenses; no prior exposure needed
• Does not discriminate the type of pathogen involved (bacteria, viruses, dust, bugs)
• Includes external and internal defenses (epithelial barriers, high acidity of secretions, phagocytosis, inflammation, fever)

Nonspecific Phagocytosis

• Neutrophils are the first to arrive at an infection site.
• Macrophages are phagocytes in specific organs (liver, spleen, lymph nodes, lungs, brain)
• They line sinusoids to remove pathogens.
• Chemokines attract phagocytes via chemotaxis.
• Phagocytes exit capillaries via diapedesis through fenestrations.

Interferons

• Polypeptides produced by virus-infected cells
• Provide resistance to viral infection in nearby cells
• Inhibit the virus's ability to replicate and assemble new virus particles

Adaptive Immunity (Specific)

• Acquired ability to fight specific pathogens after prior exposure.
• Also called the learned response
• Systemic; not restricted to a local infection site
• Has memory; mounts a stronger attack upon encountering previously encountered pathogens

Two Types of Adaptive Immunity

• Cell-mediated: T cells present antigens to killer cells. These killer cells attack infected host cells, cancer cells, and foreign cells.
• Antibody-mediated: B cells create antibodies to tag antigens for destruction. These antibodies attack bacteria and viruses.

Life of a B Cell

• Develops from a stem cell in bone marrow; sometimes stays there.
• Becomes a mature B cell (gains receptors).
• Enters lymph and blood (humoral).
• Encounters an antigen (becomes activated)
• Differentiates into plasma cells (make antibodies) and memory cells (for future exposure)

B Lymphocytes

• B cells have receptors to recognize diverse foreign antigens, usually proteins from viruses, bacteria, or allergens.
• After recognizing a matching antigen, B cells divide and produce clones.
• Differentiate into plasma cells or memory cells

Life of a T Cell

• Develops from a bone marrow stem cell.
• Moves to the thymus to mature and gain receptors.
• Proceeds to lymph and blood
• Meets an antigen (becomes sensitized).
• Differentiates into helper T cells, cytotoxic T cells, or suppressor T cells.

T Lymphocytes

• Cell-mediated immunity
• Mature in the thymus
• Activated by antigen-presenting cells (e.g., macrophages, dendritic cells, B cells)
• Activated T cells promote macrophage and lymphocyte action.

Types of T Cells

• Helper T cell (CD4): About 60-80% of T cells; secrete proteins to support other parts of the immune system (e.g., B cell growth factor and interleukins).
• Suppressor/Regulatory T cell: Prevents overactive immune responses.
• Cytotoxic/Killer T cell (CD8): Releases perforin to create pores in foreign cells, causing osmosis and destruction. Defends against viruses, fungi, and participates in transplant rejection.

Primary and Secondary Responses

• Primary Response: On first exposure to pathogens, there's a 5-10 day latency before specific antibodies are produced, plateau, and decline.
• Secondary Response: Subsequent exposure to the same antigen triggers a much faster and sustained antibody production.

Antibodies (Immunoglobulins)

• Proteins belonging to the gamma globulin class in plasma.
• Have a consistent basic structure, but differences in their components determine specificity.

Complement

• Enhances the actions of antibodies.
• Activated by pathogens (nonspecific) or antibodies (specific).
• Proteins form a pore (membrane attack complex, MAC) in the foreign cell, leading to osmotic water influx and cell lysis.

Memory Cells

• Remembers previous exposure to specific antigens.
• The primary and secondary responses highlight memory cells' impacts.
• Responds much faster and more effectively with a secondary response.

MHC Molecules

• Class I MHC molecules are found on all cells and signal to killer cells about infected cells
• Class II MHC molecules are found on antigen-presenting cells and signal to helper T cells about foreign invaders.

Interaction Between Cells

• The interaction between MHC molecules and helper or killer T cells is essential to activating the cellular and humoral arms of the immune response.

Review Questions and Answers

• Question: Which cell type shuts down immune response after infection?
• Answer: Suppressor T cells

Self-Antigens

• Human cells have unique surface proteins (self-antigens).
• Immune cells normally don't attack self-antigens.
• Foreign antigens trigger immune responses (e.g., transplant rejection).

This quiz covers key concepts in immunology, including the differences between innate and adaptive immunity, as well as the roles of T cells and B cells. Additionally, it explores the process of local inflammation and the function of phagocytes in the immune response.