The body’s defenses
Reading: Ch. 43; Keywords Lines of defense Lymphatic system Inflammation Features of immune system Memory B-cells Primary and secondary immune responses Antibody Antigen Agglutination macrophage lymphocyte Phagocytosis Complement system Humoral immunity Cell-mediated immunity B cell Helper T cell Cytotoxic T cell
Overview
Non-specific First line –Skin –Mucous membranes –Secretions of skin and mucous membranes Second line –Phagocytic white blood cells –Anti-microbial proteins –Inflammatory response
Second line of defense - macrophage
Inflamation
Focus on immune system (3rd line of defense) Protects body against specific invaders
Key features Specificity Diversity Memory Self/Nonself Recognition
First the major players: Lymphocytes
The lymphatic system
Two types of immune responses Humoral Cell-mediated
Key features Specificity Diversity Memory Self/Nonself Recognition Humoral immunity
Humoral immunity: B cells and clonal selection
There are a variety of B cells
One B cell becomes activated and proliferates
Some B cells become plasma cells that secrete antibodies
Some B cells become memory cells
Memory cells function in secondary immune response Primary immune response - first exposure Secondary immune response - second exposure
Primary and secondary immune responses
Summary Lag in primary response due to proliferation from a single clone Secondary (2°) response is from multiple memory cells 2° response has less of a lag and is stronger
What do antibodies do?
Inactivate antigens
Neutralization
Agglutination of antigen bearing particles
Precipitation of soluble antigens
Inactivate antigens Neutralization Agglutination Precipitation
These mechanisms enhance phagocytosis
Antibodies inactivate antigens Neutralization of invaders Agglutination Precipitation of soluble antigens The above enhance phagocytosis One final mechanism: Complement system
Complement system: Step 1 attachment to pathogen
Step 2: Recruitment of complement proteins
Step 3: Activation
Step 4: pore formation
Summary Complement proteins interact with antibodies to kill invading cells Binding of antibody is followed by attachment of complement proteins Protein complex becomes activated Pore is formed in pathogen’s membrane Goodbye pathogen
Two types of immune responses Humoral Cell-mediated
Complicated, involves cellular components Will briefly touch on role of helper T cells
Recall that T cells are the other type of lymphocyte
Cell-mediated response happens at the same time
Macrophage engulfs invader
Antigens from invader are presented on macrophage cell surface
Helper T cells are recruited
Helper T cells proliferate and activate cytotoxic T cells and B cells
T cells infected with HIV