The Body's Defense: Immune Cells, Proteins, and Responses

Key Components of the Immune System

Immune Cells

The immune system relies on various specialized cells to identify and eliminate pathogens:

• Neutrophils: These are phagocytic cells (microphages) that can pass through blood vessel walls in a process called diapedesis.
• Monocytes: These cells can collaborate with macrophages and lymphocytes in immune reactions.
• Lymphocytes: A crucial category of white blood cells, central to the specific immune response.
• Basophils: Contain histamine granules, which, when released, dilate blood vessels and increase capillary permeability.
• Eosinophils: Capable of performing both phagocytosis and diapedesis.

Immune Protein Molecules

Immune protein molecules are synthesized by certain immune cells and are essential for defending the body. They destroy pathogens by activating the action of other immune cells, often triggered by cytokines (protein substances synthesized by leukocytes).

The Complement System

The complement system is a set of approximately 20 proteins produced in the liver that circulate in the blood and extracellular fluid. This system of proteins acts sequentially in both localized and generalized infections. Its mechanisms of action include:

• Supporting the dilation of capillaries during infections.
• Complementing the action of immunoglobulins in destroying the cell walls of pathogens.

Immunoglobulins (Antibodies)

Immunoglobulins (Ig), commonly known as antibodies, are a group of proteins found in the blood and extracellular fluid. Synthesized by B cells, their primary role is to target foreign particles in the body. The action of immunoglobulins is based on recognizing specific molecules on pathogens, known as antigens. They bind to these antigens, effectively neutralizing the pathogenic particles and preventing them from causing harm.

Understanding the Immune Response

An immune response is a set of chemical and cellular reactions triggered by the immune system when a pathogen breaches the body's external barriers.

Nonspecific Immune Response

This response is identical for all classes of pathogens and is produced in the early stages of an attack. This type of response primarily involves neutrophils, macrophages, cytokines, and the complement system.

Specific Immune Response

This is a targeted response involving T lymphocytes, B lymphocytes, monocytes, antigen-presenting cells, and macrophages. Other participating immune molecules include immunoglobulins, cytokines, and the complement system.

Humoral Immunity

In humoral immunity, immune cells do not directly attack antigens. Instead, proteins called antibodies (or immunoglobulins), released by plasma cells, act against the antigens. Plasma cells are the activated form of B lymphocytes. This type of response is typically triggered by extracellular pathogens or bacterial toxins.

The process begins when B cells are activated by helper T cells. Once activated, B cells proliferate and differentiate into memory cells and plasma cells. The plasma cells then release specific antibodies, which lead to the opsonization of the antigen and the activation of the complement system.