Study Notes on Memory Immune Responses

Cells of Immunological Memory

This section discusses the various cells associated with immunological memory which includes Long-lived Plasma Cells, Memory T cells (subtypes CD8, TH1, TH2, TH17), as well as Memory B cells producing different classes of antibodies like IgG, IgA, and IgE, and the involvement of TFH (T Follicular Helper) cells in the adaptive immune response.

Memory Immunity

Chapter 11

Memory T Cells
  1. CD8+ T Cells - Crucial for cytotoxic functions and responding to intracellular pathogens.
  2. TH1 Cells - Important for mediating responses to intracellular pathogens, often secreting cytokines like IFN-γ.
  3. TH2 Cells - Key in responses to extracellular parasites and involved in orchestrating B cell responses.
  4. TH17 Cells - Specialized in combating fungal infections and autoimmunity, producing IL-17 among other cytokines.
Memory B Cells
  1. Antigen Recognition: Antigen recognition by T Follicular Helper (TFH) cells activates B cells.
  2. B-cell Proliferation: Activated B cells undergo proliferation generating plasmablasts which forms the primary focus.
  3. Differentiation: Further differentiation can lead to either the germinal center for high-affinity antibody production, resting memory cells for long-term survival, or antibody-secreting plasma cells.

Memory Responses

Secondary Responses

  1. Increased Cell Numbers: The secondary immune response sees a higher number of cells compared to primary responses.
  2. Efficiency: There is a quicker response to pathogens due to the memory cells.
  3. Enhanced Antibody Production: More antibodies are produced compared to the primary response.
  4. Naïve Cells Suppression: Naïve cells are suppressed to boost the response of memory cells.

Summary of Memory Immunity

Differences between Primary and Secondary Immune Responses to a Pathogen

Primary Response
  1. Cell Count: Involves a small number of pathogen-specific cells at the onset.
  2. Initial Delay: There is a delay before specific antibodies are generated.
  3. Antibody Isotype: Starts with IgM that is of low to medium affinity.
  4. Activation Threshold: Requires a high threshold of activation to initiate the response.
  5. T Cell Activation Delay: There is a delay before effector T cells are activated and can enter infected tissues.
  6. Innate Immunity: Functions independently until an adaptive response is initiated.
Secondary Response
  1. Cell Count: Involves a large number of pathogen-specific cells readily available.
  2. Pre-existing Antibodies: Specific antibodies are already present and active.
  3. Antibody Affinity: Antibodies are isotype-switched and display high affinity due to affinity maturation.
  4. Activation Threshold: Demonstrates a low threshold of activation compared to the primary response.
  5. Effector T Cells: These cells are present and activated within the infected tissue, providing immediate action.
  6. Cooperation: There is close cooperation between innate and adaptive immunity from the start of the infection.

Complications of Memory Immunity

Original Antigenic Sin

  1. Hemolytic Anemia of the Newborn

    • Occurs when the mother has memory immunity against a pathogen that the father introduces in a subsequent pregnancy.
    • Mother (-) and Father (+) scenario can create complications during the second pregnancy.

  2. Influenza Complications

    • The high mutation rate of the influenza virus can lead to complications as vaccines may not be specific enough for circulating strains during seasonal flu outbreaks.

Figure References

  1. Janeway's Immunobiology, 9th ed. (Garland Science 2017): Figure 10.3 illustrates the process of differentiation in memory B cells and the pathways involved.
  2. Differences between Primary and Secondary Immune Responses: Figure 11.15 summarizes key distinctions in memory immunity between the two response types.

These notes capture the complex dynamics of memory immunity and highlight the importance of different immune cells and their roles in both primary and secondary immune responses, as well as complications that may arise in memory immunity related to antigenic recall.