THE IMMUNE SYSTEM 1

The Perfect World The Real World HELP ME! CHICKEN POX FLU STOMACH UPSET COLD HELP ! HELP ME ! 2

Figure 15.3

Specific except for Natural killer cells B-cells

ANTIBODIES STRUCTURE CLASS 8

Distribution of immunoglobulins 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

The basic structure of immunoglobulin Heavy chain Variable domain Light chain V VH D V J J Fab VL CH1 CL CH2 Hinge region Fc CH3 Constant domain CH4 (some antibody classes only)

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

Neutralizing antibodies they represent antibodies that bind to the receptor binding site on the toxin molecule & prevent the toxin from binding to the target cell & thus protect the cell from attack

Ag-Ab interaction leads to cell lysis

Ag-Ab interaction enhance phagocytosis Antigen antibody interaction facilitates phagocytosis Ag-Ab interaction enhance phagocytosis Video film (2)

Tissues of the immune System Where B & T cells become competent to Respond to Ag

Where Adaptive IR is Initiated - Tonsils Peyer’s patches Appendix Bronchial & mammary tissue Where Adaptive IR is Initiated

Immunity is the result of the action of two types lymphocytes, the B lymphocytes and the T lymphocytes. B cells produce antibodies that are secreted into the blood and lymph.   T 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 migrated to the enemy, the next job is to EAT the microbe. The macrophage is a large phagocyte. A phagocyte is an eating cell (phago = "eating", 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