Immunity pt 2

Overview of Immune Response

• Focus on specific defenses, known as adaptive immunity.

• Unlike nonspecific defenses, adaptive immunity responds to particular pathogens (viruses, bacteria, etc.).

Antigens

• Definition: Antigens are large foreign molecules (mostly proteins) recognized by the immune system as non-self.

• Sources of antigens include:

  • Proteins from viruses, bacteria, fungi.

  • Chemicals like pollen, animal dander, and even allergens like mite feces.

• Note: High levels of allergens can irritate and provoke allergic reactions.

Adaptive Immunity

• Two main types of adaptive immunity:

  • Humoral Immunity (Antibody-Mediated): Involves B lymphocytes (B cells) producing antibodies.

  • Cell-Mediated Immunity: Involves T lymphocytes (T cells) that destroy infected cells directly.

Lymphocytes Development

• Lymphocytes originate in the bone marrow from stem cells; they mature as follows:

  • B cells: Mature in the bone marrow.

  • T cells: Leave the bone marrow immature and mature in the thymus.

• Genetic recombination allows for the production of various B and T cells to combat different antigens.

Encounters with Antigens

• Upon reaching secondary lymphatic organs (e.g., lymph nodes), mature lymphocytes encounter their corresponding antigens in lymphatic fluid.

• Activation of B cells leads to:

  • Production of antibodies (immunoglobulins).

  • Creation of memory B cells for future responses.

Antibodies Explained

• Antibodies are proteins created in response to specific antigens.

• Five classes of antibodies/immunoglobulins:

  • IgG: Most common, combats various pathogens.

  • IgA: Associated with mucosal immunity; produced in intestines.

  • IgE: Involved in allergic responses.

• Structure: Antibodies consist of a variable region (which binds to antigens) and a constant region (that stays the same).

B Cells Functionality

• An activated B cell can transform into:

  • Plasma Cells: Secrete large amounts of antibodies against the specific antigen.

  • Memory B Cells: Provide long-term immunity by swiftly producing antibodies upon re-exposure.

Dynamic of Immunity Responses

• Primary immune response may take about two weeks to develop full immunity.

• Secondary immune response is much quicker (days) due to memory cells.

• Despite memory cells, viruses can evolve (e.g., COVID variants) and evade immune detection.

T Cells Activities

• Types of T cells:

  • Cytotoxic T Cells: Directly kill infected or cancerous cells.

  • Helper T Cells: Secrete cytokines that enhance the immune response.

  • Regulatory T Cells: Help regulate and prevent inappropriate immune responses.

• T cells also form memory cells but cease to be produced in significant numbers after age 30.

Effects of Viruses on Immune Cells

• HIV attacks helper T cells, leading to immunodeficiency (AIDS) and making individuals susceptible to various cancers due to weakened immune response.

Acquiring Immunity

• Immunity can be:

  • Naturally Acquired: Infection results in immunity (examples include common colds).

  • Artificially Acquired: Through vaccinations.

• Passive Immunity: Transfer of antibodies from mother to child via placenta or breast milk; or through injections of antibodies (e.g., IgG).