OST 520 U3 EXAM - LOs LENGTHY VERSION

Primary site of early B cell development in human adults

Bone marrow (provides microenvironment, stromal cells, and IL-7 essential for pro-B cell proliferation).

Key cell surface marker present on ALL lineage-committed B cells

CD19 (along with CD20 on mature B cells, and CD21 which acts as CR2 complement receptor and EBV receptor).

Recombination enzymes required for V(D)J immunoglobulin gene rearrangement

RAG-1 and RAG-2 (Recombination Activating Genes). Deficiencies cause complete absence of B and T cells (SCID).

Enzyme responsible for N-nucleotide addition during heavy chain V(D)J recombination

TdT (Terminal Deoxynucleotidyl Transferase). Adds non-templated nucleotides to increase junctional diversity.

Definition and purpose of Allelic Exclusion in B cell maturation

Ensures that each individual B cell expresses heavy and light chains from only ONE parental allele, guaranteeing single antigen specificity per B cell.

First functional immunoglobulin heavy chain expressed in Pre-B cells

μ (mu) heavy chain, paired with a surrogate light chain (VpreB + λ5) to form the Pre-B cell receptor (Pre-BCR).

Immunoglobulin isotype expressed on the surface of Naive Immature B cells

Surface mIgM (membrane IgM). Upon fully maturing in peripheral lymphoid tissue, cells co-express surface mIgM and mIgD.

Key feature distinguishing B-1 B cells from classical B-2 B cells

B-1 cells: Arise from fetal liver, self-renew in peritoneal/pleural cavities, produce low-affinity polyreactive natural IgM antibodies without T cell help. / B-2 cells: Classical follicular B cells requiring T-cell help.

Enzyme essential for Somatic Hypermutation (SHM) and Class Switch Recombination (CSR)

AID (Activation-Induced Cytidine Deaminase). Converts cytosine to uracil in Ig V-region (SHM) and switch regions (CSR).

Molecular defect and inheritance in X-Linked Agammaglobulinemia (Bruton's XLA)

Mutation in BTK (Bruton Tyrosine Kinase). B cell maturation arrests at Pre-B cell stage. Absent peripheral B cells, severe pan-hypogammaglobulinemia, recurrent pyogenic infections after 6 months of age.

Molecular defect in Hyper-IgM Syndrome Type 1

X-linked mutation in CD40L (CD154) on activated T helper cells. B cells cannot undergo Class Switch Recombination or affinity maturation -> Elevated/normal IgM, absent IgG, IgA, IgE.

Selective IgA Deficiency clinical presentation and transfusion risk

Most common primary immunodeficiency; often asymptomatic or recurrent sinopulmonary/GI infections. High risk of severe anaphylaxis if transfused with IgA-containing blood products due to anti-IgA IgE antibodies.

Common Variable Immunodeficiency (CVID) hallmarks and age of onset

Defect in B cell differentiation into plasma cells. Normal B cell numbers but markedly decreased serum IgG, IgA, IgM. Onset usually in late teens/twenties (young adults); high risk of autoimmune disease and lymphoma.

Anatomy and functions of Germinal Center zones (Dark vs Light Zone)

Dark Zone: Rapidly proliferating centroblasts undergoing Somatic Hypermutation (SHM). / Light Zone: Centrocytes selected by Follicular Dendritic Cells (FDCs) binding antigen and T follicular helper (Tfh) cells via CD40/CD40L.

Predominant antibody isotype in mucosal secretions and dimer structure

IgA (secretory dimer held together by a J chain and wrapped by a Secretory Component derived from poly-Ig receptor).

Only immunoglobulin isotype capable of crossing the human placenta

IgG (specifically IgG1, IgG3, IgG4 via neonatal Fc receptor FcRn). Provides passive immunity to fetus and neonate.

ABO Blood Grouping genetics and natural antibody isoagglutinins

Type A: A antigen, anti-B IgM in plasma. / Type B: B antigen, anti-A IgM in plasma. / Type AB: A and B antigens, NO isoagglutinins (universal recipient). / Type O: Neither antigen, anti-A and anti-B IgM/IgG (universal RBC donor).

Rh Incompatibility (Hemolytic Disease of the Fetus and Newborn / HDFN) mechanism

Rh-negative mother sensitized to Rh-positive fetus RBCs during 1st delivery -> Mother makes anti-D IgG -> In subsequent Rh+ pregnancy, IgG crosses placenta and causes fetal erythroblastosis fetalis. Prevented with Rho(D) immune globulin (RhoGAM).

Difference between Direct Coombs Test and Indirect Coombs Test

Direct Coombs: Detects maternal IgG or complement already bound to patient's RBC surface. / Indirect Coombs: Detects unbound anti-RBC antibodies in patient's serum.

HIV viral envelope glycoproteins and host cellular receptors

gp120: Binds CD4 receptor and co-receptors (CCR5 on macrophages/T cells [M-tropic] or CXCR4 on T cells [T-tropic]). / gp41: Mediates viral membrane fusion and entry.

CD4 T-cell threshold for AIDS diagnosis and classic opportunistic infections

CD4 count < 200 cells/μL (or presence of AIDS-defining illness). / Opportunistic pathogens: Pneumocystis jirovecii (<200), Cryptococcus neoformans (<100), Toxoplasma gondii (<100), Mycobacterium avium complex (MAC) (<50).

Mechanism of action of Nucleoside Reverse Transcriptase Inhibitors (NRTIs) vs NNRTIs

NRTIs (e.g., Tenofovir, Emtricitabine): Nucleoside analogs that cause chain termination after phosphorylation. / NNRTIs (e.g., Efavirenz): Non-competitive allosteric inhibitors binding directly to reverse transcriptase.

Coombs and Gell Type I Hypersensitivity mechanism and key mediators

Type I (Immediate/IgE-mediated): Antigen cross-links IgE bound to FcεRI on mast cells/basophils -> Degranulation releasing histamine, leukotrienes (LTC4, LTD4), and tryptase. Causes anaphylaxis, asthma, hives.

Coombs and Gell Type II Hypersensitivity mechanism and clinical examples

Type II (Cytotoxic IgG/IgM): Antibodies bind tissue/cell surface antigens -> Complement activation, ADCC, or receptor dysfunction. Examples: Goodpasture, Autoimmune Hemolytic Anemia, Rheumatic Fever, Graves, Myasthenia Gravis.

Coombs and Gell Type III Hypersensitivity mechanism and clinical examples

Type III (Immune Complex): Circulating antigen-antibody immune complexes deposit in vessel walls -> Complement activation -> Neutrophil influx. Examples: Serum Sickness, Systemic Lupus Erythematosus (SLE), Post-Streptococcal Glomerulonephritis (PSGN).

Coombs and Gell Type IV Hypersensitivity mechanism and clinical examples

Type IV (Delayed T-cell mediated): CD4+ Th1 / CD8+ T cells release cytokines activating macrophages. Onset 48-72 hours. Examples: Contact dermatitis (Poison Ivy/Nickel), PPD tuberculin skin test, Type 1 Diabetes, Multiple Sclerosis.

Three essential steps of a PCR cycle and standard temperatures

1. Denaturation (~95°C): Melts dsDNA into single strands. / 2. Annealing (55-65°C): Primers bind complementary sequences. / 3. Extension (72°C): Taq DNA polymerase synthesizes new strand.

Mechanism and utility of Quantitative Real-Time PCR (qPCR / RT-qPCR)

Measures DNA/RNA amplification in real-time using fluorescent dyes (SYBR Green) or fluorophore-quencher probes (TaqMan). Quantifies viral load (e.g., HIV, HCV) and gene expression.

Diagnostic targets of Southern, Northern, and Western Blots (Mnemonic)

SNoW DROP: / Southern = DNA / Northern = RNA / Western = Protein

Principle and components of Sandwich ELISA

Measures antigen concentration: Capture antibody bound to well -> Patient sample added -> Target antigen binds -> Enzyme-linked detection antibody binds antigen -> Substrate added yielding color change proportional to antigen amount.

Utility of Flow Cytometry / Fluorescence-Activated Cell Sorting (FACS)

Analyzes single cells in fluid suspension using lasers to measure cell size (Forward Scatter / FSC), granularity (Side Scatter / SSC), and surface markers (fluorescent antibodies like CD4/CD8).

Fluorescence In Situ Hybridization (FISH) mechanism and clinical application

Fluorescently labeled DNA/RNA probes hybridize directly to intact chromosomes on slides. Detects microdeletions, duplications, and translocations (e.g., BCR-ABL t(9;22) in CML, HER2/neu amplification in breast cancer).

Genetic Information Nondiscrimination Act (GINA) protections and exclusions

Protects Americans from genetic discrimination in Health Insurance and Employment. / EXCLUSIONS: Does NOT apply to Life Insurance, Disability Insurance, Long-Term Care Insurance, or employers with <15 employees.

Ethical duty to warn family members regarding hereditary genetic risks

Physician's primary duty is to patient confidentiality. Exception/Guidance: Physician should encourage patient to inform at-risk relatives, but direct disclosure to family without consent is permitted only if harm is high probability, serious, foreseeable, and actionable.

Cardiac biomarkers: Troponin I/T vs CK-MB time course after myocardial infarction

Cardiac Troponin I/T: Most sensitive/specific; rises 3-12 hrs, peaks 24 hrs, remains elevated 7-10 days. / CK-MB: Rises 3-12 hrs, peaks 24 hrs, returns to baseline in 48-72 hrs (ideal for detecting re-infarction).

Serum Biomarkers for Heart Failure diagnosis and prognosis

B-type Natriuretic Peptide (BNP) and NT-proBNP. Released from ventricular myocytes in response to wall stretch/volume overload. High negative predictive value for heart failure.

Serum Creatinine vs Blood Urea Nitrogen (BUN) and Prerenal Azotemia ratio

Creatinine: Produced at constant rate from muscle breakdown; inversely related to eGFR. / BUN/Cr Ratio > 20:1: Indicates Prerenal Azotemia (decreased renal perfusion causing enhanced tubular urea reabsorption).

Diagnostic significance of urinary casts (RBC, WBC, Epithelial, Waxy, Hyaline)

RBC Casts: Glomerulonephritis (e.g., PSGN, IgA nephropathy). / WBC Casts: Acute Pyelonephritis, Tubulointerstitial nephritis. / Renal Tubular Epithelial Casts: Acute Tubular Necrosis (ATN). / Waxy / Broad Casts: Chronic Renal Failure. / Hyaline Casts: Nonspecific / Concentrated urine / Exercise.

Liver Function Test patterns: Hepatocellular vs Cholestatic injury

Hepatocellular Injury: Marked elevation of ALT and AST (ALT > AST in viral hepatitis; AST > ALT 2:1 in alcoholic liver disease). / Cholestatic Injury: Marked elevation of Alkaline Phosphatase (ALP) and γ-Glutamyl Transferase (GGT).

Definitions of ID50 and LD50 in microbial pathogenesis

ID50 (Infectious Dose 50): Number of pathogen cells/virions required to cause active infection in 50% of inoculated hosts. / LD50 (Lethal Dose 50): Number required to kill 50% of hosts. Lower value = higher virulence.

Exotoxins vs Endotoxins fundamental comparison

Exotoxins: Secreted proteins by Gram+ or Gram- bacteria; highly toxic; heat-labile; highly immunogenic (toxoids available). / Endotoxins: Lipid A component of LPS in Gram- outer membrane; released on cell lysis; heat-stable; triggers TNF-α and IL-1 -> septic shock.

Mechanisms of viral spread: Localized vs Systemic / Disseminated infection

Localized: Viral replication restricted to epithelial surface at portal of entry (e.g., Rhinovirus in upper respiratory tract). / Systemic: Virus invades blood/lymph (viremia) or nerves to reach distant organs (e.g., VZV, Measles).

Viral Envelopes vs Naked Capsids environmental stability and transmission

Enveloped Viruses: Lipid bilayer membrane sensitive to drying, acid, detergent, heat. Transmitted via direct contact, respiratory droplets, blood. / Naked (Non-enveloped) Viruses: Rigid protein capsid resistant to desiccation, acid, bile. Transmitted via fecal-oral route and fomites.

Transcellular vs Paracellular epithelial transport pathways

Transcellular: Solutes pass THROUGH apical membrane, cytoplasm, and basolateral membrane via active pumps/transporters. / Paracellular: Solutes/water pass BETWEEN adjacent cells through selective Tight Junctions (Zonula Occludens).

Mechanism of Intestinal Glucose Absorption (SGLT1, GLUT2, Na+/K+-ATPase)

1. Apical Entry: SGLT1 co-transports 2 Na+ and 1 Glucose into enterocyte (secondary active transport). / 2. Basolateral Exit: GLUT2 transports glucose out into blood via facilitated diffusion. / 3. Driving Gradient: Basolateral Na+/K+-ATPase pumps Na+ out to maintain low intracellular Na+.

Physiological mechanism of Oral Rehydration Therapy (ORT)

SGLT1 cotransporter requires BOTH Na+ and Glucose to function. Giving balanced solution of NaCl + Glucose forces Na+/glucose uptake, obligating massive passive water absorption to treat severe secretory diarrhea.

Tight junction regulation by Zonulin and role in Celiac Disease

Ingested gliadin binds CXCR3 -> Triggers zonulin release -> Disassembles tight junctions ('leaky gut') -> Intact gliadin enters lamina propria -> Triggers autoimmune T-cell response causing villous atrophy and blunting.

Structure and gating mechanism of CFTR (Cystic Fibrosis Transmembrane Regulator)

Member of ABC transporter superfamily, but functions as a gated ANION CHANNEL for Cl- and HCO3-. / Gating: Requires PKA phosphorylation of Regulatory (R) domain + ATP binding to Nucleotide Binding Domains (NBDs).

Tissue-specific ENaC dysregulation in Cystic Fibrosis (Sweat Glands vs Respiratory Epithelium)

Sweat Glands: CFTR normally enhances ENaC. Mutated CFTR -> Reduced ENaC activity -> Inability to reabsorb NaCl -> Hypertonic, salty sweat (>60 mEq/L Cl-). / Respiratory Airways: CFTR normally inhibits ENaC. Mutated CFTR -> Hyperactive ENaC -> Excessive Na+ and H2O reabsorbed OUT of lumen -> Dehydrated, viscous mucus plugs.

Pancreatic pathology and clinical consequences in Cystic Fibrosis

Defective CFTR causes loss of apical HCO3- and Cl- secretion in pancreatic ducts -> Acidic, dehydrated protein plugs obstruct ducts -> Autodigestion and fibrosis -> Exocrine Pancreatic Insufficiency (EPI), steatorrhea, fat-soluble vitamin (A, D, E, K) deficiency.

Definition and requirements for Bacterial Transformation

Uptake of 'naked' DNA from environment by a competent bacterium. Requires DNA Uptake Sequences (DUS) and RecA-dependent homologous recombination for chromosomal integration.

Generalized vs Specialized Transduction mechanisms and phages

Generalized: Lytic phage accidentally packages random host bacterial DNA into phage capsid. Can transfer ANY gene. / SPECIALIZED: Temperate/Lysogenic prophage excises imprecisely, dragging adjacent host genes bordering attachment site.

Standard Conjugation (F+ x F-) vs High-Frequency Recombination (Hfr x F-)

F+ x F-: Extrachromosomal F plasmid transferred via rolling circle replication through sex pilus. Recipient becomes F+. No chromosomal genes transferred. / Hfr x F-: F plasmid integrated into host chromosome. Transfers chromosomal genes. Mating bridge breaks early -> Recipient remains F-.

Evolution of Vancomycin-Resistant Staphylococcus aureus (VRSA)

Evolved via Conjugation (transfer of Vancomycin resistance plasmid from Enterococcus faecalis to MRSA) followed by Transposition (vanA transposon hopped onto native Staph plasmid).

Characteristics identifying Pathogenicity Islands (PAIs)

Large genomic regions (>30 kb) carrying multiple virulence genes. Identified by different G+C content compared to rest of host genome, flanked by direct repeats / IS elements, inserted near tRNA genes.

Definition of Chemoorganoheterotroph

Organism that obtains energy from chemical oxidation of organic compounds (chemo-organo-) and uses organic carbon as its carbon source (-heterotroph). Describes all human bacterial pathogens.

Host iron sequestration and bacterial iron acquisition mechanisms

Host sequesters free iron (10^-18 M) using transferrin, lactoferrin, ferritin, hemoglobin. Bacteria synthesize high-affinity iron-chelating molecules called siderophores (e.g., enterobactin) to steal iron.

Oxygen classification and ROS defense enzymes in bacteria

Obligate Aerobes: Require O2; have Catalase & SOD. / Obligate Anaerobes: Killed by O2; LACK Catalase & SOD. / Facultative Anaerobes: Respire or ferment; have Catalase & SOD. / Aerotolerant Anaerobes: Exclusively ferment; lack Catalase & SOD, immune to ROS because they lack ETC.

Diagnostic urine test for E. coli urinary tract infection mechanism

Facultative anaerobic E. coli respires anaerobically using nitrate (NO3-) as terminal electron acceptor, converting it to nitrite (NO2-), detected as positive Nitrite on urine dipstick.

Mechanism of Metronidazole activation in obligate anaerobes

Anaerobes use Pyruvate:ferredoxin oxidoreductase (PFOR) in fermentation -> Reduces ferredoxin -> Transfers electrons to metronidazole prodrug -> Generates toxic nitro radical intermediates that disrupt DNA.

Bacterial ribosome subunit sizes and unique translation initiation features

Bacterial 70S ribosome composed of 30S subunit (contains 16S rRNA) and 50S subunit. / Initiator amino acid is N-formylmethionine (fMet-tRNA), recognized by host innate immune system as PAMP.

Gram-negative Type III Secretion System ('Injectisome') vaccine significance

Syringe-like structure that injects virulence effector proteins DIRECTLY into host cell cytoplasm. Because effectors are never exposed to extracellular space, they are POOR targets for neutralizing antibody vaccines.

Staphylococcus aureus vs Streptococcus pyogenes key lab differentiation

S. aureus: Gram+ cocci in clusters, Catalase-positive, Coagulase-positive, yellow colonies on Mannitol Salt Agar. / S. pyogenes: Gram+ cocci in chains, Catalase-negative, Group A Lancefield, Bacitracin sensitive.

Staphylococcus aureus Protein A mechanism of immune evasion

Binds the Fc region of IgG backwards (in inverted orientation). Prevents opsonization, phagocytosis by Fc receptors, and classical complement activation.

Pathophysiology of Staphylococcal Scalded Skin Syndrome (SSSS)

Mediated by Exfoliative Toxins (ETA and ETB), which act as serine proteases that specifically cleave Desmoglein-1 (Dsg-1) in the stratum granulosum -> Intraepidermal skin sloughing without scarring.

Staphylococcal Toxic Shock Syndrome Toxin-1 (TSST-1) mechanism

Acts as a superantigen: cross-links MHC Class II on APCs to Vβ region of T-cell receptors (TCR) non-specifically -> Massive cytokine storm (IL-1, IL-2, TNF-α, IFN-γ) -> Fever, hypotension, diffuse rash, desquamation.

Coagulase-Negative Staphylococci (CoNS) key species and clinical associations

S. epidermidis: Biofilm producer on indwelling prostheses, artificial valves, catheters; Novobiocin SENSITIVE. / S. saprophyticus: 2nd most common cause of UTIs in young sexually active females; Novobiocin RESISTANT.

Streptococcus pyogenes M Protein functions and Class I disease link

Major virulence factor; forms anti-phagocytic coat binding Factor H and fibrinogen. Class I M protein strains specifically trigger Acute Rheumatic Fever.

Diagnostic test confirming recent Streptococcus pyogenes infection

ASO Titer (Anti-Streptolysin O). Streptolysin O is oxygen-labile and highly immunogenic (unlike Streptolysin S, which is non-immunogenic).

Acute Rheumatic Fever (ARF) vs Post-Streptococcal Glomerulonephritis (PSGN) prevention

ARF: Type II Hypersensitivity (anti-M protein cross-reacts with cardiac myosin). Follows pharyngitis ONLY. PREVENTED by early antibiotic treatment. / PSGN: Type III Hypersensitivity (immune complex). Follows pharyngitis OR skin infection. NOT prevented by antibiotics.

Enterotoxigenic E. coli (ETEC) toxins and intracellular messengers

LT-I (Heat-Labile Toxin): ADP-ribosylates Gsα -> Increases cAMP. / STa (Heat-Stable Toxin): Activates apical guanylate cyclase -> Increases cGMP. / Both cause hypersecretion of fluid/electrolytes (watery traveler's diarrhea).

Enteropathogenic E. coli (EPEC) attaching and effacing (A/E) lesion mechanism

Uses Type III secretion to inject Tir (Translocated Intimin Receptor) into host cell membrane -> Outer membrane Intimin binds Tir -> Host actin polymerization forms pedestal structures and effaces microvilli.

Enterohemorrhagic E. coli (EHEC / STEC) serotype, toxin, and complication

Serotype O157:H7; Sorbitol non-fermenter. / Produces Shiga Toxins (Stx-1, Stx-2) that cleave 28S rRNA (inhibiting protein synthesis). / Causes Hemorrhagic Colitis and Hemolytic Uremic Syndrome (HUS: triad of microangiopathic hemolytic anemia, thrombocytopenia, acute renal failure).

Uropathogenic E. coli (UPEC) pili types and anatomical specificity

Type 1 Pili (fim): Bind mannose residues; mediate adherence in bladder (cystitis). / Pap Pili (pyelonephritis-associated): Bind Galα(1,4)Gal glycolipids in kidney (pyelonephritis).

Neonatal Meningitis E. coli (NMEC) primary virulence factor

K1 Capsular Antigen (composed of sialic acid, identical to Neisseria meningitidis Group B capsule). Prevents phagocytosis and complement activation.

Salmonella Pathogenicity Islands SPI-1 vs SPI-2 functions

SPI-1 (T3SS-1): Mediates invasion into intestinal M cells via membrane ruffling. / SPI-2 (T3SS-2): Mediates intracellular survival inside Salmonella-Containing Vacuoles (SCV) within macrophages.

Salmonella typhi anatomical reservoir in chronic asymptomatic carriers

Persists long-term in the Gallbladder ('Typhoid Mary'), shedding bacteria continuously in bile into feces.

Streptococcus pneumoniae diagnostic identification triad

1. Gram-positive lancet-shaped diplococci. / 2. α-hemolytic on blood agar. / 3. Optochin sensitive (P-disk) and Bile soluble (lysed by deoxycholate).

Streptococcus pneumoniae Pneumolysin toxin mechanism

Cholesterol-dependent pore-forming cytotoxin released upon autolysis (LytA). Lyses ciliated epithelial cells, inhibits phagocyte respiratory burst, and activates complement.

PCV20 Pneumococcal Conjugate Vaccine immunological mechanism

Purified capsular polysaccharides conjugated to CRM197 protein carrier. Converts T-independent polysaccharide into T-DEPENDENT antigen, recruiting CD4+ T cells to induce germinal centers, high-affinity IgG, and long-term memory B cells.

Mechanism of action of β-lactam antibiotics vs Vancomycin

β-Lactams: Bind Penicillin-Binding Proteins (PBPs) and inhibit transpeptidation crosslinking. / Vancomycin: Binds D-Ala-D-Ala terminus of peptidoglycan precursors, blocking transglycosylation.

Aminoglycosides unique property and major toxicities

Only BACTERICIDAL protein synthesis inhibitors (bind 30S). Require O2 for transport. Major toxicities: Nephrotoxicity (reversible) and Ototoxicity (irreversible).

Mechanism of Sulfonamides and Trimethoprim synergistic combination (TMP-SMX)

Sulfonamides: Inhibit dihydropteroate synthase (PABA competitor). / Trimethoprim: Inhibits dihydrofolate reductase (DHFR). / Sequential blockade provides synergistic bactericidal activity.

Therapeutic Index formula and clinical interpretation

TI = TD50 / ED50 (or Toxic Dose / Effective Dose). Higher TI = wider safety window.

Competitive vs Non-Competitive Antagonist effect on Dose-Response Curves

Competitive Antagonist: Shifts curve to the RIGHT (increases EC50 / decreases potency; overcome by adding more agonist; Emax unchanged). / Non-Competitive Antagonist: Shifts curve DOWNWARD (decreases Emax / efficacy; cannot be overcome).

Potency vs Efficacy definitions on graded dose-response curves

Potency: Dose or concentration of drug required to produce 50% of its maximal effect (EC50). Curve further left = more potent. / Efficacy: Maximal response produced by a drug (Emax).

Type A vs Type B Adverse Drug Reactions (ADRs)

Type A (Augmented): Predictable, dose-dependent, related to known pharmacology (e.g., hypoglycemia from insulin). / Type B (Bizarre): Unpredictable, dose-independent, allergic/idiosyncratic (e.g., anaphylaxis from penicillin).

Cytochrome P450 Enzyme Inducers vs Inhibitors high-yield lists

Inducers: Rifampin, Carbamazepine, Phenytoin, Phenobarbital, St. John's Wort (decrease plasma levels of co-administered drugs). / Inhibitors: Ketoconazole, Erythromycin/Clarithromycin, Cimetidine, Grapefruit juice, Protease inhibitors (increase levels/toxicity).

Phases of Clinical Drug Trials (Phase I, II, III, IV)

Phase I: Small group of healthy volunteers (tests safety, pharmacokinetics). / Phase II: Small group of diseased patients (tests efficacy, dose-ranging). / Phase III: Large multi-center randomized double-blind trial (confirms efficacy vs standard/placebo). / Phase IV: Post-marketing surveillance (detects rare long-term adverse effects).

Pharmacogenomic association: TPMT deficiency and 6-Mercaptopurine toxicity

Thiopurine S-methyltransferase (TPMT) metabolizes 6-MP and Azathioprine. Genetic deficiency leads to toxic accumulation of 6-thioguanine nucleotides -> Severe life-threatening bone marrow suppression / myelosuppression.

Pharmacogenomic association: HLA-B*5701 and Abacavir

Patients carrying the HLA-B*5701 allele have a high risk of severe, potentially fatal Abacavir Hypersensitivity Reaction. Screening required prior to starting abacavir in HIV patients.

Active coenzyme form of Folate and role of Dihydrofolate Reductase (DHFR)

Tetrahydrofolate (THF). Formed from folate/DHF by DHFR. Acts as a 1-carbon carrier essential for purine and dTMP synthesis. Inhibited by Methotrexate (human) and Trimethoprim (bacterial).

Folate Trap hypothesis in Vitamin B12 deficiency

B12 is required for Methionine Synthase (converts Homocysteine + N5-methyl-THF -> Methionine + THF). B12 deficiency traps folate as N5-methyl-THF, depleting free THF needed for DNA synthesis -> Megaloblastic Anemia.

Laboratory differential diagnosis: Vitamin B12 vs Folate Deficiency

Both: Elevated serum Homocysteine, megaloblastic anemia, hypersegmented neutrophils. / Vitamin B12 Deficiency ONLY: Elevated Methylmalonic Acid (MMA) AND subacute combined degeneration of spinal cord (neurological symptoms).

Rate-limiting enzyme of Purine De Novo Synthesis and feedback inhibitors

Glutamine-PRPP Amidotransferase. Converts PRPP + Glutamine -> 5-Phosphoribosylamine. Inhibited by IMP, AMP, and GMP.

Rate-limiting enzyme of Pyrimidine De Novo Synthesis and activator/inhibitor

Carbamoyl Phosphate Synthetase II (CPS-II) (cytosolic). Activated by PRPP and ATP; inhibited by UTP.

Orotic Aciduria clinical triad and enzyme deficiency vs OTC deficiency

Deficiency in Uridine Monophosphate (UMP) Synthase (Orotate phosphoribosyltransferase + Orotidylate decarboxylase). / Triad: Orotic acid in urine, megaloblastic anemia unresponsive to B12/folate, developmental delay. / vs OTC Deficiency: OTC deficiency has hyperammonemia (UMP synthase deficiency has NORMAL blood ammonia).

Enzyme target of 5-Fluorouracil (5-FU) and Capecitabine

Thymidylate Synthase. 5-FU is converted to 5-FdUMP, which acts as a suicide inhibitor of thymidylate synthase, blocking conversion of dUMP -> dTMP ('thymine-less death').

Lesch-Nyhan Syndrome enzyme defect, genetics, and clinical triad

X-linked recessive deficiency of HGPRT (Hypoxanthine-Guanine Phosphoribosyltransferase) in purine salvage. / Triad (HGPRT): Hyperuricemia (gout), Gout, Psychomotor impairment, Retardation, Tendency toward self-mutilation (biting lips/fingers).

Adenosine Deaminase (ADA) Deficiency pathophysiology and disease

Purine degradation defect -> Accumulation of dATP, which inhibits Ribonucleotide Reductase -> Blocks all DNA synthesis -> Selective lymphotoxicity causing Autosomal Recessive Severe Combined Immunodeficiency (SCID) (absent T and B cells).