The Body’s Defenses: The Immune System

Chapter 43Part II

Two ways to fight

• Innate immunity– Defense before any exposure to pathogen

• Acquired immunity– Defense builds in response to present pathogen

Specific Defenses

• When nonspecific defense mechanisms are unable to prevent infection, the immune defense system is activated

• Product of immune system that is:1. Specific2. Diverse3. Recognizes self/non-self 4. Able to remember

• May require several days to become fully activated– Deploys extremely powerful cellular and chemical weapons

• Two types of specific defense:– Cell-mediated – Humoral

1. Specificity

• Response is not random• Recognize and eliminate particular pathogens• Body responds to antigen by releasing

antibody

Antigens

• Anything that elicits an immune response• Usually a foreign protein• Example: a cat and its dander, an

allergen/antigen for many people

Antibodies

• Proteins secreted by B cells in response to antigen presence

• Specific antibodies are produced for each antigen type

2. Diversity

The variable region (V) is different for each antigen!

3. Self/Non-self Recognition

• Blood groups, tissue grafts, and organ transplants

• Autoimmune disorders – recognition failure

• Major histocompatibility complex (MHC)– Unique proteins embedded in

plasma membrane– Class I

• Cytotoxic T cells

– Class II• Helper T cells

4. Memory

• Memory cells survive in system for a long period of time

• Activated during secondary immune response

Immune System Response

• The immune system responds in 3 essential steps:

1. Recognition of the invader (caught on the radar!)

2. Activation of the system (man your battle stations!)

3. Response to the invader (fire all weapons!)

Once the immune system has been activated…

• The response can be in the form of:– Antibodies (humoral)– Lyphocytes (cell-mediated)

Humoral Immunity• Activation and clonal

selection of B cells• Secretion of antibodies

to circulate and defend against specific antigens

• Memory cells for secondary response later

Cell-Mediated Immunity

• Activating and clonal selection of cytotoxic T cells

• Destruction of specific target cells

• Memory cells for secondary response later

Immune System

• More specific than nonspecific methods

• Memory improves response time when an invader is again encountered

• Immunity can be conferred passively or actively

Passive Immunity

• Transferred from one individual to another– Antibodies in mother’s milk

• Antibodies can be given to adults as well

• Temporary, jump-start to immunity– Work long enough to prevent

infection

Active Immunity

• Immunity acquired through individual’s own immune response– Catching a disease

• Vaccinations – Stimulate antibody

production and formation without causing the disease

– Made from killed pathogens or weakened strains

Passive vs. Active Immunity

Autoimmune Diseases

• Immune system turns against beneficial molecules in the body

• Ex: lupus– Antibodies break down

histones

Immunodeficiency Diseases

• Inability of immune system to protect the body• Ex: AIDS– Inability to produce T cells– Can’t stop HIV