Cell Recognition and Immunity

How does your blood act as a barrier of infection?

Contains platelets which clot the blood should there be a cut/wound on the skin

Describe how your airways are adapted to prevent infection.

Contain cilia and mucus. Mucus traps pathogens and cilia waft the mucus up and out of the airway.

Other than barriers to infection, name the other non-specific defense.

Phagocytosis

Describe the process of phagocytosis.

• Phagocyte engulfs pathogen

• Phagosome forms

• Lysosome fuses with phagosome forming a phagolysosome

• Lysozymes (enzyme) hydrolyses pathogen

• Soluble nutrients used and soluble debris released from the cell

What are the two main types of white blood cell?

Phagocytes and Lymphocytes

How do T cells become activated?

• Antigen presenting cell has to present a foreign antigen to the T cell

• T cell receptor complementary to the antigen binds to it and activates the T cell

Describe how T cytotoxic cells cause cell death.

• Release perforin molecule which makes holes in the cell membrane of the infected/foreign cell.

• Enzymes also release which enter the infected/foreign cell. They break the cell contents down.

• Cell is freely permeable so contents of the cell leak out and then the cell dies.

How do B cells become activated?

T helper cells

What type of cell produces and secretes antibodies?

Plasma cell

Describe how antibodies work once secreted into the blood.

• They enhance phagocytosis either by – neutralization (they bind to complementary antigens on viruses to stop it entering cells or bind to antigens on bacteria to stop it releasing toxins) or agglutination (antibodies can bind to more than one antigen at a time so it can ‘clump’ together more than one antigen at a time.