chapter 21 Pt B

Adaptive immune system

is a specific defensive system that eliminates almost any pathogen or abnormal cell in body

Characteristics of adaptive immunity

• It is specific: recognizes and targets specific antigens

• It is systemic: not restricted to initial site

• It has memory mounts an even stronger attack to “known” antigens (second and subsequent exposures)

Humoral immunity

• Antibodies, produced by lymphocytes, circulate freely in body fluids

• Has extracellular targets

Cellular Immunity

• Lymphocytes act against target cell 

  • Directly - by killing infected cells

  • Indirectly - by releasing chemicals that enhance inflammatory response, or activating other lymphocytes or macrophages

Antigens

substances that can mobilize adaptive defenses and provoke an immune response

Characteristics of antigens

• Can be a complete antigen or a hapten (incomplete)

• Contain antigenic determinants

• Can be a self-antigen

Antigenic determinants

parts of antigens that antibodies or lymphocytes’ receptors bind to

Self-antigens

all cells are covered with a variety of proteins located on the surface that are not antigenic to self, but may be antigenic to others in transfusion or grafts

Dendritic cells

Found in connective tissues and epidermis

Phagocytize pathogens that enter tissues, then enter lymphatics to present antigens to T cells in the lymph node

Macrophages

• widely distributed in connective tissues and lymphoid organs

• Present antigens to T cells, which not only activate T cells, but also further activate macrophages

B lymphocytes

• Do not activate naive T cells

• Present antigens to helper T cell to assit their own activation

Immunological Memory

Primary immune response

cell proliferation and differentiation upon exposure to antigens for the first time

Secondary immune response

Re-exposure to the same antigen gives a faster, more prolonged, and more effective response

Antibodies (Immunoglobulins (IGS))

are proteins secreted by plasma cells

• Capable of binding specifically with antigens detected by B cells

IgM

• Pentamer (larger than others); first antibody released

• Potent agglutinating agent

• Readily fixes and activates complement

IgA (secretory IgA)

• Monomer or dimer; found in mucus and other secretions

• Helps prevent entry of pathogens

IgD

• Monomer attached to surface of B cells

• Functions as B cell receptor

IgG

• Monomer: 75-85% of antibodies in plasma

• From secondary and late primary responses

• Crosses placental barrier

IgE

• Monomer active in some allegies and parasitic interctions

• Causes mast cells and basophils to release histamine