THE IMMUNE SYSTEM

• The Perfect World • The Real World

COLD

FLU

CHICKEN POX

STOMACH UPSET

HELP ME !

HELP !

HELP

ME!

Figure 15.3

B-cell

s

Specifi

c

except

for

Natural

kill

er

cell

s

ANTIBODIES

STRUCTURE CLASS

• IgG & IgM predominate in plasma while IgG &IgA are the major isotypes in extracellular fluid within the body

• IgA predominates in secretions across epithelial including breast milk. The fetus received IgG from the mother by transplacental transport. IgE is found mainly with mast cells (specially of respiratory tract, GIT & skin)

• The brain is normally devoid of immunoglobulins

J

DV

J

V

VL

CL

VH

CH1

CH2

CH3

CH4 (some antibody classes only)

The basic structure of immunoglobulin

Hinge region

Fc

Fab

Light chainHeavy chain

Constant domain

Variable domain

Antibody can be secreted from plasma cells or expressed on the cell surface of B

lymphocytes. in both forms, they recognize and bind foreign antigens

Viral infection of cells can be blocked by neutralizing antibodies

Leads to

Ag-Ab interaction leads to cell lysis

Ag-Ab interaction enhance phagocytosis

Video film (2)

Antigen antibody interaction facilitates phagocytosis

Tissues of the immune System

Primary (Central) Lymphoid Organs

Bone Marrow Thymus

Where B & T cells become competent to Respond to Ag

Secondary lymphoid organs

Spleen Lymph nodes MALT

- Tonsils- Peyer’s patches- Appendix- Bronchial & mammarytissue

Where Adaptive IR is Initiated

Immunity is the result of the action of two types lymphocytes, Immunity is the result of the action of two types lymphocytes, the the B lymphocytesB lymphocytes and the and the T lymphocytesT lymphocytes . .

B cells produce antibodies that are secreted into the blood and B cells produce antibodies that are secreted into the blood and lymphlymph . .

   T cells attack the cells that have antigens that they recognizeT cells attack the cells that have antigens that they recognize..

Killer T Cells (lymphocytes) recognize surface markers on other cells labeled for destruction. They, Killer T Cells, help to keep virus-infected or malignant cells in check.

Here, a smaller Killer T Cell (arrow) is attacking and killing a much larger flu virus-infected target. The sequence represents 30 minutes elapsed time.

• Once a white cell has left the blood vessel and Once a white cell has left the blood vessel and migrated to the enemy, the next job is to EAT the migrated to the enemy, the next job is to EAT the microbe.microbe.

• The The macrophage macrophage is a large phagocyte. A is a large phagocyte. A phagocytephagocyte is an eating cell (phago = "eating", is an eating cell (phago = "eating", cyte = "cell") which engulfs invaders. cyte = "cell") which engulfs invaders.

The scanning electron micrograph above, shows a human macrophage (gray) approaching a chain of Streptococcus pyogenes (yellow). Riding atop the macrophage is a spherical lymphocyte. Both macrophages and lymphocytes can be found near an infection, and the interaction between these cells is important in eliminating infection.

Figure 16.6