Immune System Components and Mechanisms

Macrophages and Their Functions

Macrophages originate from blood monocytes and form in the tonsils, spleen, and lymphatic vessels. They then migrate to different tissues where they are given different names. They release a substance (interleukin 1) which behaves as a second messenger that acts on the hypothalamus by altering its thermostatic function and resetting it to a higher level, causing a temperature rise. This increase stimulates the activity of leukocytes (white blood cells) and decreases the amount of iron (Fe) in the blood, which is an essential element for bacterial growth.

The Inflammatory Response Mechanism

The Inflammatory Response is a local reaction caused by the penetration of pathogens. It involves the connective tissue, blood vessels, and certain immune system components. Its purpose is to isolate and destroy pathogens and repair damage caused by them (scarring).

The Complement System and Plasma Proteins

The Complement system consists of proteins. They are a type of globulin and are always present in the plasma. Initially, these proteins are inactive and dissolved in plasma, but upon forming the antigen-antibody complex, these proteins are fixed and activate an enzyme with cytotoxic functions.

Types of Lymphocytes and Specific Responses

Lymphocytes are a type of white blood cell responsible for the specific response. They are differentiated into B and T cells:

• T-helper lymphocytes: These are cells that trigger the immune response in cooperation with macrophages and B lymphocytes.
• Cytotoxic T lymphocytes: They destroy foreign cells carrying the specific antigen and cells that have been infected. The destruction is carried out by hydrolytic enzymes which they generate.
• Suppressor T cells: These come into operation after the removal of the antigen and attenuate the immune response.

Key Characteristics of the Immune Response

• a) Memory: A few lymphocytes remain after infection; they become memory cells. Thus, after a second contact with an antigen, the production of antibodies is much faster and more numerous.
• b) Specificity: For example, a person immune to measles by having passed the disease is not immune to rubella.
• c) The distinction between self and foreign.

Classification of Immunity

Immunity can be categorized as follows:

• Natural Immunity:
  • Active: The immune system produces its own antibodies.
  • Passive: Immunity is received from another source.
• Artificial Immunity:
  • Active: The response is caused by the immune system itself (e.g., vaccines).
  • Passive: Antibodies are supplied from other individuals.