external defence mechanism

External defence mechanism

(Tissue factor)

1. Cellular factor 

2. Humoral factor (realting to body fluids immune response)

1. Cellular factor (infective agent;infect tissue)

It includes;

1. Natural killer cell

(NK cells, K cells, Killer cells)

NK play major role to kill directly tumor cells and virally infected cell without ingesting them.

2. Phagocytosis

Phagocytosis is a cellular process by which foreign particle or infectious agents are ingested and digested by phagocytic cells.

3. Inflammation

Inflammation is non specific mechanism of defence with characteristic signs of 

Redness, swelling, heat, pain and altered function.

Types of inflammatory response 

1. Localized Inflammation

2. Systemic inflammation

4. Pyrexia (Fever)

Stimulates the phagocytic activity and inhibits the growth of microorganisms.

The fever decreases the iron level in the body (because iron promotes growth of bacteria).

Fever also increases the production of interferon.

2. Humoral factor

Humoral factor includes;

1. Complement

It enhances phagocytosis and kill most of G-ve bacteria.

2. Interferons

Interferon is a natural antiviral substance which inhibits intracellular viral replication.

3. Bactericidin

Kill bacteria 

4. Lysozyme

Bactericidal enzyme found in tears, nasal/ intestinal secretion and other body fluids.

5. Beta-lysin

Able to kill some Gram +ve bacteria.

6. Properdin

Lysis of gram -ve bacteria and inactivates some Viruses.

7. Basic polypeptides

Bactericidal substances acting upon cell wall of bacteria.