Immune Response Mechanisms

Immune Response Mechanisms

1. Overview of Immune Response

   • The immune response is the body's defense mechanism against pathogens.
   • It involves a complex network of cells, tissues, and organs.

2. Types of Immune Responses

   • Innate Immunity:
     • First line of defense; rapid and non-specific.
     • Components include physical barriers (skin, mucous membranes), phagocytes (macrophages, neutrophils), natural killer cells, and the complement system.
   • Adaptive Immunity:
     • Slower response; specific to pathogens.
     • Involves lymphocytes (B cells and T cells) and the formation of memory cells.

3. Phagocytosis

   • Process where phagocytes engulf and digest pathogens.
   • Key players: macrophages and neutrophils.
   • Steps include:
     • Recognition of pathogens.
     • Engulfment.
     • Digestion within phagolysosomes.

4. Antibody Production

   • B cells produce antibodies in response to antigens.
   • Antibodies neutralize pathogens and mark them for destruction.
   • Types of antibodies:
     • IgM: First response.
     • IgG: Most abundant, provides long-term immunity.
     • IgA: Mucosal immunity.
     • IgE: Involved in allergic reactions.

5. T Cell Activation

   • T cells recognize antigens presented by Major Histocompatibility Complex (MHC) molecules.
   • Types of T cells:
     • Helper T cells (CD4+): Activate B cells and cytotoxic T cells.
     • Cytotoxic T cells (CD8+): Destroy infected or cancerous cells.
   • Activation requires two signals: antigen recognition and co-stimulation.

6. Cytokines and Immune Regulation

   • Cytokines are signaling molecules that mediate and regulate immunity.
   • Key types include:
     • Interleukins (IL): Promote growth and differentiation of immune cells.
     • Tumor Necrosis Factor (TNF): Involved in systemic inflammation.
     • Interferons: Antiviral responses.

7. Memory Response

   • After the initial response, memory B and T cells are formed.
   • Provide faster and stronger responses upon re-exposure to the same pathogen.

8. Humoral vs. Cell-Mediated Immunity

   • Humoral Immunity: Mediated by antibodies produced by B cells; effective against extracellular pathogens.
   • Cell-Mediated Immunity: Involves T cells; effective against intracellular pathogens and cancer cells.

9. Pathogen Recognition

   • Pathogen-associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRRs) on immune cells.
   • Examples of PRRs include Toll-like receptors (TLRs).

10. Resolution of Immune Response

    • Involves the removal of pathogens and return to homeostasis.
    • Regulatory T cells and cytokines play crucial roles in downregulating the immune response after infection clearance.

Overview of Immune Response

• Immune response serves as the body's primary defense mechanism against pathogens, involving a network of cells, tissues, and organs.

Types of Immune Responses

• Innate Immunity:
  • The first line of defense, quick to react and non-specific.
  • Comprises physical barriers like skin and mucous membranes, phagocytes (macrophages, neutrophils), natural killer cells, and the complement system.
• Adaptive Immunity:
  • A slower response characteristic tailored to specific pathogens.
  • Involves lymphocytes: B cells (produce antibodies) and T cells (coordinate immune responses), along with the development of memory cells for future protection.

Phagocytosis

• A process where phagocytes, particularly macrophages and neutrophils, engulf and digest pathogens.
• Steps include:
  • Recognition of pathogens,
  • Engulfment into the cell,
  • Digestion within specialized compartments called phagolysosomes.

Antibody Production

• B cells produce antibodies in response to antigen exposure.
• Antibodies serve to neutralize pathogens and tag them for destruction.
• Key types of antibodies include:
  • IgM: First antibody produced in response to infection,
  • IgG: Most prevalent, provides long-term immunity,
  • IgA: Key for mucosal immunity,
  • IgE: Associated with allergic responses.

T Cell Activation

• T cells recognize antigens presented by Major Histocompatibility Complex (MHC) molecules.
• Types of T cells:
  • Helper T cells (CD4+): Activate B cells and cytotoxic T cells,
  • Cytotoxic T cells (CD8+): Target and kill infected or cancerous cells.
• Activation requires dual signals: antigen recognition and co-stimulation.

Cytokines and Immune Regulation

• Cytokines function as signaling molecules that regulate various immune functions.
• Important types include:
  • Interleukins (IL): Facilitate immune cell growth and differentiation,
  • Tumor Necrosis Factor (TNF): Engages in systemic inflammation responses,
  • Interferons: Play a role in antiviral defense.

Memory Response

• After initial immune response, memory B cells and T cells are generated.
• These cells enable quicker and more effective responses upon re-encountering the same pathogen.

Humoral vs. Cell-Mediated Immunity

• Humoral Immunity:
  • Driven by antibodies produced by B cells, effective against extracellular pathogens.
• Cell-Mediated Immunity:
  • Involves T cells and targets intracellular pathogens and cancer cells directly.

Pathogen Recognition

• Immune cells identify pathogens through pathogen-associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRRs).
• An example of PRRs is Toll-like receptors (TLRs), pivotal in initiating immune responses.

Resolution of Immune Response

• The process of eliminating pathogens and restoring homeostasis includes the roles of regulatory T cells and various cytokines, crucial for downregulating the immune response post-infection.