Untitled Quiz

Immune System Overview

• The immune system has two main branches: innate and adaptive.
• Innate immunity acts quickly, providing immediate response (minutes to hours).
• Adaptive immunity takes longer to activate (days to weeks), but responds faster upon re-exposure due to memory cells.

Innate Immune System

• Non-specific; recognizes broad categories of pathogens (e.g., bacteria, viruses) using generic pathogen-associated molecular patterns (PAMPs).
• Lacking memory; each encounter with a pathogen triggers the same response.
• Key components: Physical barriers (skin, mucous membranes), cells (macrophages, neutrophils, dendritic cells, natural killer (NK) cells), and soluble factors (cytokines, complement proteins).

Adaptive Immune System

• Highly specific; recognizes unique antigens on pathogens using specific receptors on B and T cells.
• Possesses immunological memory; upon re-exposure to the same pathogen, memory B and T cells facilitate a faster, stronger response.
• Key components: Cells (B cells, T cells - helper and cytotoxic), and antibodies (immunoglobulins) targeting pathogens specifically.

Diversity of Response

• Innate immunity has limited diversity, using a fixed set of receptors to recognize PAMPs.
• Adaptive immunity has highly diverse receptors for specific antigens due to genetic recombination in B and T cells.

Role in Immune Response

• Innate immunity serves as the first line of defense, managing infections and activating adaptive immunity.
• Adaptive immunity provides long-lasting, targeted response and resolves infections that innate immunity cannot.

Summary Table

Antigen, Epitope, and Hapten

• Antigen: Any substance that can be recognized by the immune system and elicits an immune response. Can be monovalent, multivalent, or polyvalent.
• Epitope: Specific region on an antigen that is recognized by immune receptors.
• Hapten: A small molecule that is not immunogenic on its own but becomes immunogenic when bound to a larger carrier protein.

Pattern Recognition Receptors (PRRs)

• Specialized receptors on immune cells recognizing pathogen-associated molecular patterns (PAMPs) on pathogens.
• Types include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs).
• Critical for innate immune system, providing a first line of defense.
• Expressed on various innate immune cells (macrophages, dendritic cells, neutrophils, NK cells) and even some non-immune cells (epithelial cells).

T and B Cell Receptors

• B cell receptors (BCRs): Membrane-bound immunoglobulins (Ig) found on B cells. Recognize whole antigens directly.
• T cell receptors (TCRs): Membrane-bound proteins on T cells. Require antigen processing and presentation by MHC molecules. Recognize only processed peptides.

Types of Antigens

• Proteins: Often stimulate strong immune responses.
• Carbohydrates: Recognized by BCRs.
• Lipids and Nucleic Acids: Can be recognized by BCRs, especially when part of complex structures.

B-Cell Activation

• Triggered by antigen binding to B cell receptors (BCRs).
• Requires co-stimulation from helper T cells (T-dependent antigens) or cross-linking of multiple BCRs (T-independent antigens) to activate a signaling cascade.
• Differentiates into plasma cells, producing large amounts of antibodies, or memory B cells for future responses.
• Class switching (isotype switching): Changing antibody class to better target specific pathogens or tissues (e.g., from IgM to IgG).
• Affinity maturation: Increasing antibody affinity for the antigen through somatic hypermutation and selection.

T-Cell Activation

• Requires antigen presentation by antigen-presenting cells (APCs) on MHC molecules.
• Requires co-stimulatory signals from the APC (e.g., CD28 interacting with B7 molecules).
• Differentiates into various subsets of helper T cells (Th1, Th2, etc.) and cytotoxic T cells (CTLs), with different functions.
• Cytokines play a critical role in guiding T cell differentiation and function.

Types of Hypersensitivity Reactions

• Type I (Immediate): IgE-mediated; rapid response involving mast cells and basophils (e.g., allergies).
• Type II (Cytotoxic): IgG or IgM antibodies directly attack target cells (e.g., blood transfusions, autoimmune hemolytic anemia).
• Type III (Immune Complex): Immune complexes deposit in tissues, activating complement and causing inflammation (e.g., systemic lupus erythematosus).
• Type IV (Delayed): T cell-mediated; delayed response involving macrophages and T cells (e.g., contact dermatitis, tuberculin skin test).

Immune Checkpoint Inhibitors

• Inhibitory receptors on T cells (e.g., PD-1, CTLA-4) can be targeted for cancer immunotherapy.
• Blocking these receptors can unleash T cell responses to tumor cells to fight cancer.

Graft Types

• Autografts: (Low immunogenicity) self-tissue transplant within same individual.
• Isografts: (Low immunogenicity) identical twin transplant or genetically identical animals.
• Allografts: (High immunogenicity) transplant between two genetically different individuals of the same species.
• Xenografts: (Very high immunogenicity) transplant between individuals of different species.

Transplant Rejection

• Hyperacute: pre-existing antibodies quickly attack graft.
• Acute: T cells and antibodies recognize graft as foreign.
• Chronic: persistent low-level immune response damages the graft over time.
• Graft vs Host: donor immune cells attack recipient's tissues.

Immunosuppressive Agents

• Calcineurin inhibitors: Inhibit calcineurin, reducing IL-2 production (e.g., cyclosporine, tacrolimus).
• mTOR Inhibitors: Block mTOR signaling pathways involved in T cell proliferation (e.g., sirolimus).
• Antimetabolites: Inhibit nucleotide synthesis necessary for DNA and RNA replication. (e.g., mycophenolate mofetil).

Immune Responses to Intracellular Viruses

• Involves innate immune responses (interferons primarily) and adaptive responses (cytotoxic T cells primarily).
• Viruses replicate inside cells, the strategy to target these differs from extracellular bacteria.

Immunological Assays

• Immunodiffusion: Precipitation reactions in agarose gels visualize antibodies/antigens interactions.
• Hemagglutination: Clumping of red blood cells (RBCs) to detect presence of antibodies/antigens.
• ELISA: Enzyme-linked antibodies detect antigens/antibodies with color changes.
• Immunoblot (Western blot): Proteins are separated by electrophoresis and transferred to a membrane. Detected by specific antibodies to identify proteins.
• Immunofluorescence: Fluorescently labeled antibodies/antigens are visualized using a microscope.