Innate and Acquired Immunity

Helminth Immunity

• Helminths are too large to be engulfed by phagocytes, and their integument is resistant to microbicidal products of neutrophils and macrophages.
• However, they can be killed by histamine, a basic protein present in the granules of eosinophils.
• IgE coats the helminths, allowing eosinophils to bind to the IgE and destroy the helminths.

Immunity Classification

• Humoral Immunity: mediated by antibodies (B cells), defends against extracellular microbes and microbial toxins.
• Cell Mediated Immunity: mediated by T cells, acts against intracellular pathogens.

Cell Mediated Immunity

• Composed of T-lymphocytes, responds to intracellular pathogens.
• Activated lymphocytes attach to and destroy foreign agents.
• Acts when antibodies are ineffective due to inaccessibility to the antigen.

Types of Effector T Cells

• Regulatory T cells:
  • T-helper cells: interact with antigen-MHC II complex, potentiate engulfment and killing by phagocytosis, and promote growth and differentiation of cells at the immune response site.
  • T-regulatory (suppressor) cells: suppress the activity of B cells and other T cells, inhibit antibody production, and suppress the functions of killer T cells and helper T cells.
• Cytotoxic (killer) T cells (CD8+): interact with antigen-MHC I molecule, actions mediated by cytokines, lead to destruction of virus-infected cells, tumor cells, or foreign cells.

Cell Mediated Immunity Reaction Steps

• Naïve T cell recognition of cell-associated antigens in peripheral lymphoid organs.
• Clonal expansion of T cells and their differentiation into effector cells.
• Migration of effector T cells to the site of infection or antigen challenge.
• Elimination of the microbe or antigen.

Basis of Mode of Development

• Active Immunity: lymphocytes produce their own antibodies in response to stimulation by the antigen.
  • Artificial active immunity: provided by vaccination.
  • Natural active immunity: provided by natural infection.
• Passive Immunity: the body receives antibodies from an external source.
  • Natural passive immunity: IgG antibody produced in mother crosses the placenta and protects the fetus up to 6 months old.
  • Artificial passive immunity: preformed antibodies are injected into the host for immunity (e.g., anti-venom, Rabies vaccine).

Characteristics of Innate and Adaptive Immunity

• Innate Immunity: antigen-independent, no time lag, non-specific, no immunologic memory.
• Adaptive Immunity: antigen-dependent, lag period, specific, development of memory.

Innate Immunity

• Natural Killer (NK) Cells: lyse viral-infected body cells and abnormal cells that could form tumors.
• Involved in the internal defense, attracting phagocytes to the infected area.

Acquired/Adaptive Immunity

• Acquired Immune System: also referred to as "specific immunity", third line of defense.
• Works slowly, involving antigen-specific immune response, recognizing, attacking, destroying, and remembering each pathogen.
• Produces specialized cells and antibodies that render pathogens harmless.