There are two fundamental types of immunity: Innate or Inborn (inherited) immunity and Acquired or Adaptive immunity.
i. Innate Immunity:
Innate immunity is the genetically inherited resistance to infections.
It serves as the natural defense system of the body, not influenced by prior contact with microorganisms or immunization.
This non-specific immunity provides a general degree of resistance to infection.
It encompasses various barriers preventing the entry of foreign agents into the body.
a. Epithelial Surface: The intact skin and mucous membranes act as barriers, protecting against microbial invasion. Healthy skin, with high salt concentrations in drying sweat, has bactericidal properties. The mucosa of the respiratory tract employs innate defense mechanisms.
b. Antimicrobial Substances: The complement system, interferons, and various proteins in blood and tissues contribute to eliminating pathogens.
c. Cellular Factors: Phagocytic cells, including macrophages and neutrophils, play a crucial role in removing foreign particles. Natural killer (NK) cells provide non-specific defense against viral infections and tumors.
d. Fever: Increased body temperature accelerates physiological processes, aiding in pathogen destruction.
e. Acute-phase Proteins: Infection or injury leads to a surge in certain plasma proteins, enhancing host resistance and promoting inflammatory lesion repair.
ii. Acquired Immunity:
Acquired immunity, or Adaptive immunity, involves the formation of antibodies that neutralize antigens.
a. Active Immunity: Resistance developed due to antigenic exposure, categorized as natural or artificial.
b. Passive Immunity: Acquired through the receipt of pre-made antibodies, not involving active participation by body cells. Passive immunity can occur naturally or artificially.