Immune System Overview

Immune System Cells & Tissues

• The immune system is triggered by antigens, which are toxins or foreign substances that induce an immune response.
• Antigens, often proteins, peptides, or polysaccharides, can originate from within the body (self-antigen) or from the external environment (non-self).
• Vaccines are antigens that can trigger the adaptive immune system to produce memory to a specific disease, inducing immunity to it.

Immune Response Branches

• The immune response has two main branches: innate and adaptive.
• The innate response is the first line of defense, providing an immediate, non-specific response to pathogens.
• Adaptive immunity develops over time, providing long-lasting immunity with high specificity for certain antigens.

Innate Immunity

• Components of innate immunity include physical barriers (skin, mucous membranes), chemical barriers (enzymes, stomach acid), and immune cells (natural killer cells, macrophages, neutrophils).
• The innate response is non-specific, but responds to a broad range of pathogens.
• The response is extremely fast—occurring within minutes or hours of exposure to pathogens.
• Innate immunity has no immunological memory; the response is the same each time a pathogen is encountered.
• The innate immune system relies on pattern recognition receptors (e.g., TLRs) that find pathogen-associated molecular patterns (PAMPs).

Adaptive Immunity

• The adaptive immune response relies on B-cells (which produce antibodies) and T-cells (helper and cytotoxic) for defense against a specific pathogen.
• The adaptive immune response is highly specific, targeting specific antigens.
• The response typically takes several days or more to fully develop, with a key aspect being the development of immune memory for future encounters.
• Adaptive immunity relies on receptors that can be somatically recombined from existing diversity to detect specific antigens.

Antigen-Presenting Cells (APCs)

• APCs, like dendritic cells, macrophages, and B cells, capture antigens from pathogens or damaged cells, process them, and display them on their surface to T-cells.
• APCs play a critical role in initiating the adaptive immune response by presenting antigens to T-cells.
• Antigen presentation involves the uptake of antigens, their processing into smaller fragments, loading these fragments onto major histocompatibility complex (MHC) molecules, and displaying these MHC-antigen complexes on the cell surface.
• This presentation triggers the activation of specific T-cells.

Lymphocytes

• Lymphocytes (B and T cells) are key players in adaptive immunity.
• B cells mediate humoral immunity, producing antibodies targeting pathogens.
• T cells mediate cell-mediated immunity, targeting infected or cancerous cells.
• Several types of T cells exist, with different functions (e.g., Cytotoxic T cells, Helper T cells).
• Different classes of T cells and NK cells require specific activation cues to respond to infection.

Effector Cells

• Effector cells (T cells, macrophages and granulocytes) eliminate antigens
• They function by directly attacking and killing infected or abnormal cells
• Several different types of granulocytes have different roles in immunity.

Immune System Tissues and Organs

• Generative lymphoid organs (Bone Marrow and Thymus) are where immune cells are made and mature.
• Secondary lymphoid organs (Lymph nodes and the Spleen) play a critical role in activating immune responses (specifically, adaptive).
• Mucosal-associated lymphoid tissue (MALT) protects mucosal surfaces.
• These tissues work together to facilitate the encounter and activation of immune cells.

This quiz covers essential concepts of the immune system, including the roles of different immune cells and tissues. Explore the mechanisms behind innate and adaptive immunity, and learn how antigens trigger immune responses. Perfect for biology students seeking to strengthen their understanding of immunology.