Topic 2: Cells of the Immune System

Presented by Essence Perry

Immune System ●The immune system is the

biological structures and processes within an organism that protects against foreign substances by identifying and killing pathogens and tumor cells.

●It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly.

Cell Groups Immune cells are divided into two groups…

I. Lymphocytes: Derived in bone marrow from lymphoid stem cells. Help develop the ACQUIRED immune system.

II.Granulocytes: Cells have large granules in their cytoplasm. Help develop the INNATE immune system.

Adaptive Immunity●The humoral immune response occurs in

the blood and lymph, which were long ago called body humors (fluids). In the humoral response, antibodies help neutralize or eliminate bacteria, bacterial toxins, viruses. and pathogens in the blood and lymph.

●In the cell-mediated immune response, specialized T cells destroy infected host cells. Defense against cancer cells, virus-infected cells, fungi, animal parasites, and foreign cells from transplants.

Lymphocytes I. B cells II. T cellsIII.Natural Killer

cells

I.B cell Progenitor (B cell)Mature in bone marrowStored and mature in spleen Involved for humoral immunity: response is

mediated by antibody molecules that are secreted by plasma cells to prevent intracellular infections

Once activated by antigen, proliferate into two clones of cells: plasma cells that secrete antibodies and memory cells that may be converted into plasma cells at a later time

Perform antigen processing and presentationDifferentiate into two types of B cells:

○ Plasma cells ○ Memory B cells

B Cells continued… Memory B Cells

●Remain “in reserve” so if same pathogen appears, the cells can immediately differentiate into cytotoxic and helper T cells, causing a swift secondary response to the invasion

●Help gain immunity from future infections

B Cells continued… Plasma Cells

●A type of immune cell that makes large amounts of a specific antibody.

●Plasma cells develop from B cells that have been activated.

●A plasma cell is a type of white blood cell. Also called plasmacyte.

II. T cell Progenitor●Developed from stem cells in

the bone marrow●Mature in the thymus ●Involved in cell-mediated

immunity●Activated when another cell

presents antigen to them●Several types of T cells (T

cells differentiate into… )○ Cytotoxic T cells○ Helper T cells○ Suppressor T cells

T Cells continued… Cytotoxic T Cells

●The term cytotoxic refers to their use of toxic gene products to kill infected cells.

●To become active, they require signaling molecules from helper T cells and interaction with a cell that presents an antigen.

●Once activated, cytotoxic T cells can eliminate cells that are infected by viruses or other pathogens

T Cells continued… Helper T Cells

●Cells triggers both the humoral and cell-mediated immune responses.

●Helper T cells themselves do not carry out those responses.

●Instead, signals from helper T cells initiate production of antibodies that neutralize pathogens and activate T cells that kill infected cells

T Cells continued… Suppressor T Cells

● Activated more slowly than the other T cells

● Inhibit the response of the immune cells to prevent potential “autoimmune” response

III. Natural Killer Cells ●Circulate through the body and

detect the abnormal surface proteins of some virus-infected and cancerous cells.

●Able to bind to certain tumor cells and virus-infected cells without the stimulation of antigens, and kill them by the insertion of granules containing perforin

●Inhibits the growth of cancer

Granulocytes I. Neutrophils II. EosinophilsIII.Basophils IV.Mast Cell V. Monocytes

A. Dendritic CellB.Macrophage

I. Neutrophils ● Circulate in the blood● Are attracted by

signals from infected tissues and then engulf and destroy the infecting pathogens

II. Eosinophils ●Discharge destructive enzymes

● As soon as a parasite enters the body, a chemical signal is sent out that the eosinophils recognize and tells them exactly where the intruders are located

●Especially important in defense against parasitic infections

III. Basophils ●Have large histamine-

containing granules that stain dark blue

●Release histamine (an inflammatory chemical that makes blood vessels leaky and attracts other WBCs to the inflamed site, and causes dilation of the blood vessels)

●Aid in allergic and antigen response by releasing the rarest WBC

IV. Mast Cell ●Release histamine

●IgE antibodies bind to mast cells and release histamine and other inflammatory chemicals from granules (vesicles)

Monocytes ● Present pieces of

pathogens to T cells so that the pathogens may be recognized again and killed, or so that an antibody response may be mounted.

Dendritic Cells ●Important in alerting and activating

immune system cells to a threat such as bacterial or viral invasion

●With their long, wispy extensions, dendritic cells are very efficient antigen catchers.

●Once they have engulfed antigens by phagocytosis, they enter nearby organ where they will present the antigens to T cells.

●Most effective antigen presenters known, it’s their only job.

Macrophage ● Monocytes that have migrated out

of the bloodstream and into the body tissues are macrophages

● Engulf and destroy necrotic cell debris and foreign material including viruses, bacteria, and tattoo ink

● Extends long pseudopods to crawl through tissue to reach infected site

● Lysosomes within the cell digest the infectious microorganisms it engulfs

● Central actors in the final disposal of cell debris as the inflammation stops

● Are important in fighting chronic infections, such as tuberculosis

● Cytokines help develop the large appetites of macrophages