The Immune System: Mechanisms of Defense

Innate Immunity: Non-Specific Defenses

The innate immune system provides immediate, non-specific protection against a wide range of pathogens. This involves physical barriers like skin and mucous membranes, chemical defenses such as stomach acid and antimicrobial peptides, and cellular components including phagocytes (macrophages, neutrophils) that engulf and destroy invaders. The complement system, a group of proteins that enhance phagocytosis and directly kill pathogens, also plays a crucial role.

Inflammation

A vital innate response characterized by redness, swelling, heat, and pain. It involves the recruitment of immune cells to the site of infection or injury, promoting pathogen clearance and tissue repair.

Adaptive Immunity: Specific Defenses

The adaptive immune system mounts a targeted response to specific pathogens. This involves lymphocytes, namely B cells and T cells, which recognize unique antigens on pathogens. This response exhibits immunological memory, leading to faster and more effective responses upon subsequent encounters with the same pathogen.

Humoral Immunity (B cells)

B cells produce antibodies, proteins that bind to specific antigens, neutralizing pathogens, and marking them for destruction by other immune cells. Plasma cells are antibody-producing effector B cells, while memory B cells provide long-lasting immunity.

Cell-Mediated Immunity (T cells)

• Cytotoxic T cells (CD8+): Directly kill infected cells by releasing cytotoxic molecules.
• Helper T cells (CD4+): Orchestrate the immune response by releasing cytokines that activate other immune cells, including B cells and cytotoxic T cells.
• Regulatory T cells: Suppress the immune response to prevent excessive inflammation and autoimmunity.

Lymphoid Organs

Specialized organs, including the bone marrow, thymus, spleen, and lymph nodes, are essential for the development, maturation, and function of immune cells.

Immunological Memory

Following an infection, memory B and T cells persist, allowing for a rapid and more effective response upon subsequent exposure to the same pathogen. This is the basis of vaccination.

Dysfunction of the Immune System

Immune deficiencies, autoimmune diseases, and allergies represent disruptions in the normal functioning of the immune system, leading to increased susceptibility to infections or inappropriate immune responses against self-antigens.