Resistance and Immunity

The human body is under constant attack from a wide range of invaders. The body has to face these attacks from conception in the womb till the end of life. These invaders include diverse entities such as bacteria, viruses, parasites and cancer cells. The body has thus developed protective mechanisms to survive.

These protective measures can be divided into two categories:

Non-specific defense mechanisms: Non-specific defense mechanisms are not specialized for a particular kind of invader. There are two types of non-specific defense mechanisms:

  1. First line of defense: Barriers such skin and mucous membranes
  2. Second line of defense: Internal defenses such as leukocytes and anti-microbial proteins

Specific defense mechanisms: Specific defense mechanisms can be grouped under the term immunity. The immune system can be considered the third line of defense. It consists of mechanisms and agents that target specific antigens. An antigen is any molecule that can be identified as foreign (nonself) or self and stimulates an immune response. An antigen may be a toxin, viral protein, or molecules present in the plasma membranes of bacteria or other foreign cells. Once the antigen is recognized, the immune system releases an agent which targets that specific antigen.

Topics in this section

  • Non-specific defence mechanisms
    • Defence at body surfaces
    • Phagocytosis
    • Natural antimicrobial substances
    • The inflammatory response
      • Acute inflammation
      • Chronic inflammation
      • Fibrosis (scar formation)
    • Immunity
      • Cell-mediated immunity
      • Antibody-mediated (humoral) immunity
      • Acquired immunity
    • Hypersensitivity (allergy)
      • Type I, anaphylactic hypersensitivity
      • Type II, cytotoxic hypersensitivity
      • Type III, immnune-complex-mediated hypersensitivity
      • Type IV, delayed type hypersensitivity
    • Autoimmune diseases
    • Immunodeficiency
      • Acquired immune deficiency syndrome (AIDS)