4th exam part 3

Adaptive Immune Response

• Adaptive immunity removes specific pathogens and remembers them for future encounters.

Division of Labor

• Humoral immunity targets extracellular pathogens.
• Cellular immunity targets intracellular pathogens.
• Innate immunity recognizes Pathogen-Associated Molecular Patterns (PAMPs).

Adaptive Immunity

• Adaptive immunity involves induced resistance to specific pathogen components.

Cells of the Immune System

• The diagram shows a branching lineage of immune cells, starting from stem cells. 
• Lymphoid stem cells give rise to lymphocytes (B cells, T cells, and natural killer cells).
• Myeloid progenitor cells give rise to granulocytes (neutrophils, eosinophils, basophils, and mast cells), monocytes, dendritic cells, and macrophages.

Phagocytic Cells

• Non-specific phagocytic cells recognize PAMPs.

• Examples include dendritic cells and macrophages.

• These cells have multiple receptors to recognize different pathogens.

• Specific phagocytic cells recognize only one shape.

• T cells recognize antigens with T cell receptors.

• B cells recognize antigens with immunoglobulin receptors.

Dual Nature of Adaptive Immunity

• B and T cells originate from stem cells in the bone marrow.
• Humoral immunity involves B cells maturing in the bone marrow (Bursa of Fabricius in chickens).
• Antibody production is the key effect of humoral immunity.
• Cellular immunity involves T cells maturing in the thymus.
• T cells directly attack pathogens.

Adaptive Response

• Adaptive immunity is triggered by antigens; two types are described.
• T-independent antigens trigger a strong signal that leads to B or T cell proliferation and differentiation.
• Pathogens are then attacked by the generated cells.
• T-dependent antigens trigger a weaker signal which needs confirmation from helper T cells. 
• Helper T cells further stimulate B and T cells' growth and development for attacking pathogens.

Antigens

• Antigens are molecules that trigger an immune response.
• Some antigens are proteins, others are carbohydrates.
• Antigens are often small, sometimes 5-9 amino acids.
• Self-antigens are normal body proteins.
• Non-self antigens are foreign.

Antigen Presentation

• Antigen presentation involves presenting antigens on MHC molecules.
• MHC (major histocompatibility complex) molecules are crucial for antigen presentation.

Quality Control

• In cells, there's random sample testing and proteasome processes to identify and eliminate defective or dangerous cells.
• The Major Histocompatibility Complex (MHC) is like a quality control system, checking for normal cells.

Summary

• B and T immune cells work together to respond to threats.

More on Antigens

• Self antigens are made by normal cellular metabolism and are presented on cell surfaces.
• External antigens are proteins and other molecules from outside the body, processed by cells, and displayed on special receptors.

Stop and Catch Up

• Questions to prepare before moving on include details about different types of antigens.
• Comparisons of MHC I and MHC II molecules

More in General

• Antigen-presenting cells (APCs) break down pathogens into smaller fragments.
• These fragments act as distinct patterns, recognized by matching receptors like locks and keys.

Immune cells

• Immune cells are “preadapted” in the sense that their potential responses to different shapes are already defined.

Immune System Overview

• Involves innate and acquired immunity components, reacting immediately to pathogens or later with adaptive immunity.

T Lymphocytes Overview

• Cytotoxic T cells induce apoptosis in infected or cancerous cells that express MHC class I.
• Helper T cells activate B cells and other immune cells. 

T Lymphocytes Antigen Recognition

• Helper T cells (CD4) respond to antigens presented by MHC class II molecules on antigen-presenting cells (APCs).

T Lymphocytes in B cell Activation

• Helper T cells (Th cells) are crucial for activating B cells, leading to antibody production and B memory cells.

Humoral Response Summary

• B cells create a clone of identical cells, which result in secreted antibodies
• Primary response happens upon initial encounter with an antigen.
• Secondary response happens upon subsequent encounter, with memory cells.

Natural Killer Cells

• Natural killer (NK) cells are part of the innate immune system, lacking antigen specificity but recognizing antibody-coated cells or infected by viruses without MHC.