Ebmp+Ap+Bio+Project+V2

Chapter 43: The Immune System

By Phenix Messersmith

Evan Schwartz

Brian Shea

Mike Gaunt

Innate Immunity: Nonspecific Defense Mechanisms

• External - first line of defense: called barrier defense (ex. skin, mucous membranes, and secretions of skin and mucous membranes)

• Internal – second line of defense: phagocytic white blood cells, antimicrobial proteins, the inflammatory response

The Inflammatory Response

• Four main steps:• #1- chemical signals cause capillaries to widen • #2- fluid, other clotting elements move to site of

injury; clotting begins• #3- Chemokines released by various cells attract

more phagocytic cells to injury cite• #4- Neutrophils and macrophages engulf

pathogens and cell debris. Tissue heals.

Leukocytes

• Phagocytic white blood cells: neutrophils, macrophages, eosinophils, and dendritic cells

• Engulfs infected bacteria and infected tissue

• Discharges destructive enzymes

Acquired Immunity: Specific Defense

• Third line of defense• Examples: lymphocytes (white blood cells)

and antibodies (proteins secreted by B cells)• Able to distinguish one inducing agent from

another• Fight against antigens (foreign molecule

that elicits a specific response by a lymphocyte)

Different Types of Lymphocytes

• B Lymphocytes (B cells) – develop in bone marrow; after encountering antigens they change to antibody-secreting plasma cells (the effector cells of humoral immunity)• T Lymphocytes (T cells) – develop in the thymus;

after encountering antigens they are responsible for cell mediated immunity

More On B Cells

• Antigens bind to specific receptors and cytokines secreted from helper T cells then activate B cells

• Once activated they generate antibody-secreting effector cells or plasma cells

MHC: Major Histocompatibility Complex

• Responsible for stimulating the immune response of T cells by binding to antigens so that T cell receptors can recognize them

• Process called antigen presentation

Different Types of T Cells

• Cytotoxic T Cells- kill infected cells, cancer cells, and transplanted cells after being activated by recognizing Class I MHC molecules

• Helper T Cells- secrete cytokines that promote response of B cells and cytotoxic T cells to antigens when activated by recognizing Class II MHC molecules

The Lymphatic System

• A system of vessels and lymph nodes separate from the circulatory system that returns fluid and protein to the blood

• Stores and reproduces macrophages and other such white blood cells who fight off infections

Antibodies

• Aid in immunity by:

• 1- viral neutralization (blocks binding to host)

• 2- opsonization (increases phagocytosis)

• 3- agglutination (forms aggregates that can be readily phagocytosed by macrophages)

• 4- precipitation (of soluble antigens dissolved in body fluids)

Primary Response vs. Secondary Response

• Initial acquired immune response to an antigen which peaks about 10 to 17 upon first exposure

• When the same antigen enters the body and the response is faster, about 2 to 7 days, because there are more antibodies in the blood

Active vs. Passive Immunity

• Active: long-lasting, conferred by action of B and T cells and resulting B and T memory cells specific for pathogen

• Passive: Short-term, conferred by administration of ready made antibodies or the transfer of maternal antibodies to fetus or nursing infant

Allergies

• Hypersensitive responses to certain environmental antigens, called allergens

• Scientists believe allergies are evolutionary remnants of immune system’s response to parasitic worms

HIV: Human Immunodeficiency Virus

• Retrovirus that gains entry into the cells by using different cell types, such macrophages and brain cells, that have low levels of CD4 as receptors and co-receptors

• Main receptor for HIV is the CD4 molecule on helper T cells, this infection and loss of helper T cells allows the rise of AIDS