BIOL 470W Week 6 notes

Lymphatic system

Network of tissues, vessels, and organs that help rid the body of toxins, waste, and unwanted materials while transporting lymph.

Lymph

Clear-to-white fluid made of white blood cells (especially lymphocytes) circulating through the lymphatic system.

Lymph nodes

bean-shaped organs that filter lymph and store white blood cells to help fight infection.

Associated lymphoid tissues

MALT and other mucosal-associated lymphoid tissues that monitor mucosal surfaces for foreign antigens.

Primary and secondary lymphatic organs

primary organs (bone marrow and thymus) are where lymphocytes form and mature; secondary organs (lymph nodes, spleen, MALT) are where mature lymphocytes interact with antigens.

Hematopoiesis

The production and formation of all types of blood cells and platelets, occurring primarily in the bone marrow.

Pluripotent stem cell

A master stem cell in the bone marrow that can give rise to any type of blood cell line.

Leukocytes

White blood cells involved in defending the body against infectious disease and foreign invaders.

Erythrocytes

Red blood cells responsible for carrying oxygen throughout the body.

Platelets

small cell fragments in the blood involved in clotting and wound healing.

Neutrophils / PMN

Polymorphonuclear leukocytes; the most abundant white blood cells and rapid primary responders in acute inflammation.

Monocytes

Large white blood cells that circulate in the blood and differentiate into macrophages and dendritic cells in tissues.

Macrophages

Large phagocytic white blood cells that engulf pathogens, cellular debris, and dead cells.

Dendritic cell

Professional antigen-presenting cells that bridge innate and adaptive immunity by presenting antigens to T cells.

Antigen-presenting cells (APCs)

Cells (macrophages, dendritic cells, B cells) that process and display peptide antigens on MHC molecules to T cells.

Cytokines

Small secreted proteins crucial for cell signaling, immune response modulation, and intercellular communication.

Chemokines

A specialized subset of cytokines that induce directed chemotaxis (movement) in nearby responsive immune cells.

Interferons

Signaling proteins released by host cells in response to viral pathogens to interfere with viral replication.

PAMP (Pathogen-Associated Molecular Patterns)

Conserved molecular structures found on broad groups of pathogens that are recognized by innate immune receptors.

PAMPR / PRR (Pattern Recognition Receptors)

germline-encoded proteins of the innate immune system that detect signature molecules associated with microbial invaders or cellular stress; exogenous molecules on microorganisms

Anti-microbial peptides

Small molecular weight proteins that serve as a fast first-line chemical defense by disrupting microbial membranes.

Chelators

Molecules that tightly bind metal ions (such as free iron), withholding essential nutrients from pathogens.

CD markers

Cluster of Differentiation cell-surface molecules used to identify and immunophenotype different types of immune cells.

MHC I and II (Major Histocompatibility Complex)

MHC I is found on all nucleated cells (presents endogenous antigens to cytotoxic T cells); MHC II is found on professional APCs (presents exogenous antigens to helper T cells).

Immunoglobulins

Y-shaped protein antibodies produced by plasma cells to neutralize or tag foreign targets.

T cell receptor (TCR)

Molecule on the surface of T cells responsible for recognizing antigen fragments presented on MHC molecule

B cell receptor (BCR)

Transmembrane receptor protein on the surface of a B cell that recognizes intact foreign antigens.

Antigen

Any substance (usually foreign) that binds to an immune receptor and induces an immune response.

Epitope

The specific part or site of an antigen molecule that is directly recognized by an antibody, B cell receptor, or T cell receptor.

Antibody

Soluble glycoprotein produced by plasma cells designed to bind specific epitopes and neutralize or clear pathogens.

Agglutination

the clumping together of particulate cells, bacteria, or particles by antibodies.

Neutralization

The process where antibodies or molecules block a pathogen or toxin from binding to or entering host cells.

Opsonization

Coating a pathogen with molecules (like antibodies or complement proteins) to flag it for enhanced phagocytosis.

Lipases

Bacterial enzymes that break down lipids and fats, assisting pathogens in colonizing skin and tissues.

Protein A

Surface protein produced by Staphylococcus aureus that binds the Fc region of IgG antibodies to evade phagocytosis.

: Enterotoxin

A protein exotoxin released by microorganisms that targets the intestinal tract, often causing food poisoning symptoms.

Intoxication

Illness caused by ingesting preformed microbial toxins rather than a live bacterial infection.

Exfoliative toxin

Toxins produced by Staphylococcus aureus that split intracellular bridges in the epidermis, causing skin to peel off (scalded skin syndrome).

Toxic Shock Syndrome Toxin – 1 (TSST-1)

A potent superantigen produced by Staphylococcus aureus that triggers massive, systemic cytokine release and shock.

Describe the barriers in the first line of defense against infections.

Physical barriers (skin, mucosal membranes), chemical barriers (acidic pH, antimicrobial peptides, lysozyme in tears/saliva), and normal microbiota outcompeting pathogens.

Explain how cells of the innate immune response differentiate self from non-self.

Innate immune cells use germline-encoded Pattern Recognition Receptors (PRRs) to detect invariant Pathogen-Associated Molecular Patterns (PAMPs) unique to microbes, distinguishing them from host structures.

Explain how cells of the adaptive immune response differentiate self from non-self.

Major Histocompatibility Complex (MHC) molecules, somatically generated T-cell and B-cell receptors (TCRs/BCRs), and strict central and peripheral tolerance selection processes

Differentiate between innate and adaptive immunity.

Innate immunity is rapid, non-specific, has no memory, and uses PRRs; adaptive immunity is slower initially, highly specific, develops immunological memory, and uses somatically rearranged receptors (TCRs/BCRs).

Describe 4 ways the innate immune response kills or inhibits pathogens.

1) Phagocytosis by neutrophils and macrophages, 2) Complement system activation (direct lysis and opsonization), 3) Inflammation induction to recruit immune cells, 4) Antimicrobial peptides and enzymes (like lysozyme) breaking down cell walls.

Describe the process of T and B cell activation and the role of these cell types in immunity.

B cells bind antigens via BCR and receive helper T cell signals to differentiate into antibody-secreting plasma cells. T cells are activated when their TCR recognizes processed antigens on MHC molecules presented by APCs alongside co-stimulatory signals, prompting proliferation and helper/cytotoxic functions.

Explain why multiple signals for the activation of T and B cells is beneficial.

T and B cells is beneficial primarily to prevent accidental activation, protect the body from autoimmune reactions, and ensure a targeted, high-affinity immune response

Compare and contrast thymus-independent (TI) and thymus-dependent (TD) antigens.

TD antigens (proteins) require T cell help, leading to class switching, affinity maturation, and strong memory. TI antigens (usually polysaccharides) can stimulate B cells directly without T cells, yielding weaker responses, limited isotype switching, and minimal memory.

Describe the mechanism by which TD antigens stimulate a stronger B cell response than TI antigens.

TD antigens engage CD4+ T cell help through MHC II presentation, triggering germinal center reactions, somatic hypermutation, affinity maturation, and robust memory B cell formation. TI antigens activate B cells on their own through direct receptor cross-linking

Describe the mechanism of action of staphylococcal lipases, exfoliative toxin, and toxic shock syndrome toxin.

• Lipases: Break down lipids/sebum to facilitate skin colonization.

• Exfoliative toxin: Cleaves desmoglein-1 in epidermal cell junctions, causing blistering and skin shedding.

• TSST-1: Acts as a superantigen, non-specifically bridging MHC II and TCRs to cause an uncontrolled cytokine storm.

design and carry out a strategy to isolate and identify members of the staphylococci and micrococci in the laboratory.

Inoculate a selective/differential medium like Mannitol Salt Agar (MSA): Staphylococci: Beta (ferments mannitol yellow) ; Growth will occur due to the 7.5% NaCl concentration

Micrococci: They do not ferment mannitol; gamma;

catalase test: both are positive

Modified Oxidase: Staph is negative, micro is positive (purple)

Lysostain: micrococci is senstive, stapj is not

Explain the mechanism of action of beta-lactam resistance in MRSA

MRSA acquires the mecA gene, which encodes an altered penicillin-binding protein (PBP2a) that has very low affinity for beta-lactam antibiotics, allowing cell wall synthesis to continue in their presence.

Compare and contrast community-acquired and healthcare-associated MRSA.

CA-MRSA occurs in healthy individuals without recent healthcare exposures, typically causes skin/soft tissue infections, and carries smaller SCCmec types (IV or V) along with PVL toxins. HA-MRSA occurs in patients with healthcare facility exposures, is frequently multi-drug resistant, and typically harbors larger SCCmec types (I, II, III).