Learning objectives
• Define immunity
• Classify types of immunity
• Differentiate between innate & acquired immunity
• Describe characteristics of innate and acquired immunity.
• Describe clinical importance of both types.

Body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells.

Internal defense system that plays key role in recognizing and either destroying or neutralizing materials within the body that are foreign to the normal self.

• Pathogen:
– Disease producing microorganism as virus & bacteria.
• Virulence:
– Disease producing power of pathogen.

1. Defending against invading pathogens.
2. Removing worn out cells & damaged tissues, paving the way for wound healing & repair.
3. Identifying & destroying abnormal/mutant cells (Immune surveillance)---defense against cancer
4. Mounting inappropriate immune responses which lead either to allergies or autoimmune diseases .

Effector cells of immune system
• Leukocytes and their derivatives, along with a variety of plasma proteins.
• Most leukocytes are out in the tissues on defense missions.
• So are widely dispersed throughout the body and can defend in any location.

• Natural immunity, Inherent or inbuilt,
Non specific
• Eliminates pathogen before development of disease.
• First line of defense against pathogens.
• Mechanism involved in innate immunity:
– Phagocytosis by WBCs & macrophages
– Enzymes & acid of GIT
– Stratum corneum of skin
– Lysozymes, basic polypeptides ,
complement complex, NK cells

• Adaptive / specific immunity.
• Develops against specific foreign bodies.
• Extremely powerful immune response.
• LYMPHOCYTES are responsible for this response.

1. Cell mediated immunity (T lymphocytes)
2. Humoral immunity (B lymphocytes)