BY 312 Lecture (3/30)

Adaptive Immunity Overview

• Adaptive immunity discussed, with a focus on the role of epitopes as antigens.

• Importance of phagocytosis in initiating adaptive immunity:

  • Innate immunity must occur first to trigger the adaptive immune response.

Role of Antigen Presenting Cells (APCs)

• Definition and Importance: Antigen presenting cells (APCs) include dendritic cells and macrophages that bridge the innate and adaptive immunity.

  • Dendritic cells have projections known as dendrites, distinct from neuronal dendrites.

  • Typically located in external environment-contacting tissues (e.g., skin, mucous membranes).

Mechanism of Antigen Presentation

• Phagocytosis by APCs involves engulfing and destroying invaders and presenting isolated antigens to helper T cells.

• Helper T cells (CD4 cells):

  • Significance of T cell activation after recognizing foreign antigens.

  • Initiates a cascade leading to the activation of B cells for antibody production and cytotoxic T cells for direct attack on pathogens.

Immune Response Activation and Types

• Activated helper T cells facilitate immune response, leading to:

  • Formation of cytotoxic T cells (CD8) that annihilate foreign entities.

  • B cells that produce antibodies.

• Distinction between two types of adaptive immunity:

  • Antibody-mediated immunity: Involves B cells transforming into plasma cells that secrete antibodies.

  • Cell-mediated immunity: Involves cytotoxic T cells.

Clonal Selection

• Clonal Selection Process:

  • Lymphocyte proliferation and differentiation occurs in response to specific antigens.

  • This produces clones of cells that can recognize the same antigens as the original.

• Memory T and B cells are generated for quicker future responses.

Co-stimulation Mechanism

• Definition: Co-stimulation refers to the required second signal for T cells to become activated upon binding to an antigen.

• Role of cytokines in this process.

• Various co-stimulator types, particularly cytokines, help with T cell activation and subsequent immune functions.

Major Histocompatibility Complex (MHC)

• MHC molecules play a vital role in distinguishing self from non-self:

  • Present antigens to T cells, essential in immune response.

  • Two classes of MHC:

  • MHC I: Present on almost all nucleated cells, interacts with cytotoxic T cells.

  • MHC II: Restricted to APCs, presents antigens to helper T cells.

Cytotoxic T Cell Action

• Mechanisms of cytotoxic T cell action:

  • Perforins: Induce cytolysis by creating pores in infected cells.

  • Granulysin: Dismantles pathogens upon entry through created pores.

  • Lymphotoxin: Activates enzymes that induce DNA fragmentation in target cells, causing cell death.

Cytokines and Their Role

• Cytokines act as signaling molecules coordinating immunity:

  • Include interferons, interleukins, erythropoietin, and tumor necrosis factor.

• Functions:

  • Interferons combat viral replication.

  • Erythropoietin (EPO) influences red blood cell production.

Antibodies (Immunoglobulins)

• Structure of antibodies:

  • Composed of two heavy chains and two light chains, connected by disulfide bonds forming a Y-shaped molecule.

• Functions:

  • Neutralization of pathogens.

  • Activation of the complement pathway.

  • Enhancement of phagocytosis (opsonization), drawing more phagocytes to the site.

Conclusion of Session

• Discussion wraps, leaving topics for the next class.

• Notes highlight the interrelation of various immune processes, showcasing the complexity of adaptive immunity.